Plants Used in Constructed Wetlands for Aquaculture: A Systematic Review

Abstract

The latest FAO report indicates that aquaculture accounts for 51% of the global production volume of fish and seafood. However, despite the continuous growth of this activity, there is evidence of the excessive use of groundwater in its production processes, as well as pollution caused by nutrient discharges into surface waters due to the water exchange required to maintain water quality in fishponds. Given this context, the objectives of this study were as follows: (1) to review which emergent and floating plant species are used in constructed wetlands (CWs) for the bioremediation of aquaculture wastewater; (2) to identify the aquaculture species whose wastewater has been treated with CW systems; and (3) to examine the integration of CWs with recirculating aquaculture systems (RASs) for water reuse. A systematic literature review was conducted, selecting 70 scientific articles published between 2003 and 2023. The results show that the most used plant species in CW systems were Phragmites australis, Typha latifolia, Canna indica, Eichhornia crassipes, and Arundo donax, out of a total of 43 identified species. These plants treated wastewater generated by 25 aquaculture species, including Oreochromis niloticus, Litopenaeus vannamei, Ictalurus punctatus, Clarias gariepinus, Tachysurus fulvidraco, and Cyprinus carpio, However, only 40% of the reviewed studies addressed aspects related to the incorporation of RAS elements in their designs. In conclusion, the use of plants for wastewater treatment in CW systems is feasible; however, its application remains largely at the experimental scale. Evidence indicates that there are limited real-scale applications and few studies focused on the reuse of treated water for agricultural purposes. This highlights the need for future research aimed at production systems that integrate circular economy principles in this sector, through RAS–CW systems. Additionally, there is a wide variety of plant species that remain unexplored for these purposes.

1. Introduction

Aquaculture is described as the organized breeding, feeding, propagation, or protection of aquatic resources for commercial or public purposes [1]. In Mexico, according to the General Law on Sustainable Fisheries and Aquaculture, it is defined as a set of activities aimed at the controlled reproduction, pre-fattening, and fattening of aquatic fauna and flora species, carried out in facilities located in freshwater, marine, or brackish environments. These practices involve breeding or cultivation techniques for species that are suitable for commercial, ornamental, or recreational exploitation [2].

Since its origins over 4000 years ago, aquaculture has been used to produce food and other commercial products, including ornamental species, sanitary products, pharmaceuticals, and substrates for various commercial applications [3]. Today, aquaculture has evolved into a major global food-producing industry valued at USD 312.8 billion. It represents 59% of the combined fishery and aquaculture production. For the first time, aquaculture has surpassed capture fisheries, contributing 94.4 million tons, equivalent to 51% of global aquatic animal production, and reaching a record 57% of the production destined for direct human consumption [4]. These figures highlight aquaculture as a crucial sector within the global food system.

In this context, the fisheries and aquaculture industries play an essential role in the global supply of food. It is projected that aquatic animal production will increase by 10% by 2032, driven by the expansion of aquaculture [4,5]. Aquaculture’s contribution to the global supply of high-quality protein for human consumption is vital for food security and nutrition. Aquatic animal products provide 15% of the animal protein and 6% of the total protein consumed worldwide, in addition to essential nutrients such as omega-3 fatty acids, minerals, and vitamins [6]. However, these projections are alarming, as aquaculture production will need to increase to 129 million tons by 2050 to meet the growing global demand [5,6,7,8,9].

To address this challenge, the FAO’s Blue Transformation Roadmap 2022–2031 is aligned with the declarations of the Committee on Fisheries (COFI). Its goal is to lay the groundwork for ensuring sufficient supplies of aquatic foods for a growing population. This strategy considers the three dimensions of sustainability: environmental, social, and economic dimensions [10,11,12]. Equity is also a priority, with a focus on guaranteeing the availability and accessibility of safe and nutritious aquatic foods, especially for vulnerable populations [13].

From the social sustainability perspective, significant improvements are needed globally [14]. It is estimated that aquaculture directly employs 61.8 million people in primary production activities, mainly in small-scale operations. The disaggregated data by gender shows that women represent 24% of fishers and aquaculture workers, while they account for 62% of the workforce in post-harvest sectors [4]. In Mexico, there are 271,431 registered people engaged in fishing and aquaculture activities; of these, 222,744 are dedicated to fishing and aquaculture fisheries, and 48,687 are involved in controlled aquaculture systems [15]. This activity not only generates income but also provides food and employment opportunities for populations in both coastal regions and inland aquaculture areas [16,17,18]. Despite its importance, aquaculture remains concentrated in a small number of countries, while many low-income nations in Africa, Asia, Latin America, and the Caribbean have yet to fully realize its potential [4].

1.1. Problem Statement

From an environmental perspective, the rapid growth of aquaculture production systems has increased concerns about resource overexploitation and the associated environmental impacts. Despite its contribution to regional development, critical issues such as the management of pollutants from aquaculture wastewater, water scarcity, and the depletion of water resources have often been overlooked or received limited attention [19,20]. It is therefore necessary to study the inherent environmental impacts of any industry, and aquaculture is no exception. There is an ongoing debate among scientists regarding the environmental impacts of this “blue revolution,” with concerns suggesting that global aquaculture is not sustainable when analyzed through the lenses of food, energy, water, and carbon. A particular emphasis has been placed on the discharge of untreated aquaculture wastewater [14,21,22,23,24,25,26,27,28].

In some cases, aquaculture has been documented to negatively impact both marine and freshwater ecosystems by increasing disease transmission, introducing non-native species through escapes, releasing nutrient-rich waste and residues, and causing the destruction of wetlands. These factors contribute to water pollution, disrupting both the ecological balance and wildlife habitats [29,30,31].

Evidence indicates that the global sustainability pattern of aquaculture shows a significant variation between continents and countries. While most countries demonstrate social benefits and intermediate environmental costs, suggesting a balance between costs and benefits, results reveal that two-fifths of the 161 countries analyzed in 2018 achieved a high sustainability score (>50). This indicates a considerable need for improvement in aquaculture sustainability worldwide [14]. Therefore, bold and forward-looking measures are required to achieve the objectives outlined in the Declaration for Sustainable Fisheries and Aquaculture and to support the 2030 Agenda [13].

It is important to highlight that, within aquaculture operations, water use, energy costs, and feed expenses are among the most significant factors in semi-intensive and intensive systems [26,32,33,34]. Thus, innovation and research are vital to mitigate these costs and to promote the recovery and competitiveness of small- and medium-sized aquaculture enterprises (SMEs) in coastal, urban, and rural areas [10,35].

1.2. The Background on Ecotechnologies for the Treatment of Aquaculture Wastewater

The current state of the research regarding technologies that support the environmental sustainability of the aquaculture industry demonstrates the potential for implementing various systems. These include Integrated Multi-Trophic Aquaculture (IMTA), Integrated Agri-Aquaculture Systems such as aquaponics (AQ), Recirculating Aquaculture Systems (RAS), Biofloc Technology (BFT), the more recent Aquamimicry technology (AT), In-Pond Raceways Systems (IPRS), the combination of BFT and RAS (BIO-RAS), and Partitioned Aquaculture Systems (PAS) [27,36,37]. Additionally, symbiotic technologies based on plant fermentations, such as Bioaquafloc (BAF), are being developed [38,39,40].

These systems offer the advantage of water reuse through closed systems with minimal water discharge, in contrast to traditional open-flow systems that discharge untreated wastewater. This wastewater typically contains nutrient particles, primarily phosphorus and nitrogen [41,42,43]. Such nutrients can be removed through the sedimentation of suspended solids in tanks or mechanical filters, the nutrient reduction via irrigation in agricultural crops, or the use of constructed wetlands (CWs) [44,45,46,47,48,49,50,51,52].

Although wastewater treatment and reuse methods have been reported in aquaculture production, most of them require high capital investments and operational costs [53]. In this regard, constructed wetlands (CWs) represent an ecotechnology that mimics the functions of natural wetlands within a controlled environment. CW systems typically consist of a series of cells with substrates and plants, where wastewater flows through a porous medium designed for purification. These systems facilitate processes such as filtration, solids retention, nutrient removal, pathogen and microorganism elimination, and water oxygenation [49,54,55]. As such, they can be considered Nature based solutions (NbSs) [56].

Constructed wetlands can play a vital role in aquaculture, providing a low-cost alternative for treating aquaculture wastewater compared to other technologies [50,57,58,59,60,61]. However, their study has been relatively underexplored [62] and often limited to a few aquaculture species [49]. Some studies have reported remarkable removal efficiencies, with ammonia nitrogen (NH₄⁺) removal rates of 86–98%, nitrite (NO₂⁻) removal rates over 99%, nitrate (NO₃⁻) removal rates between 82 and 99%, total nitrogen (TN) removal rates from 95 to 98%, phosphate removal rates from 55 to 71.2%, biochemical oxygen demand (BOD₅) reductions from 25 to 55%, and suspended solids (SSs) removal rates from 47 to 86% [63,64].

The mechanisms for removing organic and inorganic compounds, as well as pollutants such as nitrogen (N) and phosphorus (P) present in aquaculture water, are carried out by plants. Through their roots, stems, and leaves, plants are capable of directly absorbing inorganic forms of nitrogen present in the pond, such as ammonium and nitrate [45]. In addition, the roots provide support for microbial communities and help capture suspended particles and pollutants, transporting nutrients to other parts of the plant, such as stems and leaves, to promote growth. The effectiveness of the contaminant removal improves when plants have more developed root systems. On the other hand, additional key processes for water purification occur within the substrate, where most of the physicochemical and biological activity takes place [54]. Within this system, microorganisms play a crucial role in nitrogen removal, as they metabolize nutrients and transform them into less harmful compounds. This process, known as microbial denitrification, includes stages such as ammonification, nitrification, and denitrification. As a result, various forms of nitrogen (NH₃⁺, NO₂⁻, and NO₃⁻) can be effectively removed from the water, thus improving the quality of the aquaculture effluent [55]. These compounds are among the most critical to remove from production ponds and aquaculture wastewater [26,33,37]. Therefore, an appropriate design, vegetation selection, and substrate type are essential to improve the treatment of aquaculture wastewater and to support microbial activity within the controlled wetland environment [65,66]. Typha spp. and Phragmites australis spp. are the most commonly used species in constructed wetlands.

1.3. The Justification for the Literature Review

The treatment of wastewater is a critical and challenging issue in the aquaculture industry, as it affects surface and groundwater resources, fish production, energy consumption, and water reuse for agricultural purpose areas where there is still limited evidence [27,62]. Therefore, the appropriate selection of plant species to be used in constructed wetlands (CWs) for wastewater treatment is an essential criterion. Not all species are tolerant of aquaculture wastewater conditions; some may not survive or may fail to perform their functions adequately. Consequently, the treatment efficiency of CWs systems could be directly impacted by the selected plant species [67].

1.4. The Relevance and Practical Implications of the Research

Considering the global importance of aquaculture and its environmental impacts—particularly the pollution of water bodies—there is a pressing need worldwide to promote sustainable aquaculture practices. Constructed wetlands (CWs) represent an ecotechnology that has seen a limited application within the aquaculture sector. For this reason, focusing on the remediation of aquaculture wastewater, especially groundwater, through innovative methods is essential [68,69,70]. This study addresses a knowledge gap by synthesizing the role and significance of plant species that have proven to be effective in the bioremediation of aquaculture wastewater.

From a theoretical perspective, this review is significant because there is currently no comprehensive scientific literature that specifically focuses on the importance of plant species used in CWs for aquaculture wastewater treatment. In terms of practical application, this study is highly relevant. In Mexico alone, there are 4623 registered aquaculture farms [71]; the majority of which lack wastewater treatment systems. CWs could be integrated into these farms to mitigate environmental impacts caused by wastewater discharges, offering a low-cost alternative compared to conventional treatment technologies [33,35,53].

There is empirical evidence indicating that CWs are a viable option for sustainable aquaculture when implemented appropriately [50,57,58]. However, the number of studies and literature reviews focused on CWs in aquaculture remains limited. Based on this, the following research questions are proposed:

• RQ1. Which floating and emergent plant species have been used in constructed wetlands for bioremediation in aquaculture?
• RQ2. Which aquaculture species have had their wastewater treated with constructed wetlands?
• RQ3. Have constructed wetland systems been integrated into recirculating aquaculture systems (RAS)?
• RQ4. Is there evidence of full-scale studies or real-world applications?

Therefore, the objective of this study is to review the emergent and floating plant species used in constructed wetlands (CWs) for the bioremediation of aquaculture wastewater, to identify aquaculture species whose wastewater has been treated with CWs, and to explore the integration of CWs with recirculating aquaculture systems (RASs) for water reuse in food production and the efficient use of surface and groundwater resources.

2. Materials and Methods

2.1. The Planning of the Systematic Literature Review

The systematic literature review (SLR) was conducted with the aim of identifying and analyzing the current state of knowledge regarding the use of constructed wetlands (CWs) for the treatment of aquaculture wastewater, as well as the plant species employed in these systems. The review followed the PRISMA 2020 guidelines [72], which provide a structured and transparent framework for literature selection and analysis. (Supplementary Materials: PRISMA checklist for systematic reviews AQ-CW).

2.2. Inclusion and Exclusion Criteria

The following selection criteria were established to include only the most relevant articles capable of answering the research questions.

Inclusion criteria:

• Studies focused on the application of constructed wetland technologies—vertical flow, horizontal flow, and hybrid systems—in any configuration, used in freshwater and marine aquaculture systems.
• Peer-reviewed research articles published in scientific journals.
• Publications in any language, covering the period from 2003 to 2023, to reflect recent advances in this underexplored field and focus on studies providing relevant empirical evidence.

Exclusion criteria:

• Studies that do not report information relevant to the research questions.
• General review articles, book chapters, theses, or documents that are not original research articles.
• Articles for which the full text was not available.
• Studies published outside the defined time frame (2003–2023).
• Research not specifically addressing the application of CWs in aquaculture.
• Studies lacking information regarding the country where the research was conducted, the aquaculture species cultivated, the vegetation used, whether the system was coupled to a recirculating aquaculture system (RAS), and the study’s scale.

2.3. Study Selection and Data Collection

The SLR was carried out in five distinct stages involving the search, selection, and review of relevant studies in the field of constructed wetlands applied to aquaculture wastewater treatment.

In the first stage, Google Scholar alerts were configured using keywords in English: Constructed wetlands/Aquaculture, Plants/Bioremediation, Environmental impact/Aquaculture, and Aquaculture wastewater treatment. These alerts were reviewed daily by email for one year, due to the limited availability of information. In addition, searches were conducted in major academic databases such as ScienceDirect, Scopus, and ResearchGate using the same keywords in different combinations and permutations. Recent reviews on the topic and original research articles were also considered. The initial search yielded 10,966 articles.

In the second stage, the preliminary filtering of results was performed according to the defined inclusion and exclusion criteria, reducing the number of articles to 3588. The full texts of these articles were reviewed, and reference lists were checked to identify additional relevant studies.

During the third stage, the remaining 117 articles underwent a thorough full-text review. After applying the exclusion criteria, 27 articles were removed, resulting in a final sample of 70 potentially relevant studies.

In the fourth stage, these 70 articles were independently evaluated by the authors. By consensus, they agreed to include all 70 articles in the systematic review.

Finally, in the fifth stage, each article was analyzed using content analysis techniques and a structured content analysis guide [73] as the data collection instrument.

The systematic process of searching, selecting, and analyzing the studies is illustrated in the PRISMA flow diagram (Figure 1). The findings of each study were qualitatively synthesized and summarized in tables and graphs in accordance with the objectives of this research. A systematic literature review was conducted, selecting 70 scientific articles published between 2003 and 2023.

3. Results and Discussion

3.1. Historical Evidence on the Treatment of Aquaculture Wastewater Using Constructed Wetlands

The application of constructed wetland (CW) systems in aquaculture was pioneered by Schwartz and Boyd [74], who implemented these systems for channel catfish (Ictalurus punctatus) production. Their CWs were planted with California bulrush (Scirpus californicus), giant cutgrass (Zizaniopsis miliacea), and maidencane (Panicum hemitomon). They concluded that a Hydraulic Residence Time (HRT) of 1 to 4 days, with Hydraulic Loading Rates (HLRs) ranging from 77 to 91 L per square meter per day (L/m²/day), was adequate. The study reported reductions in the following parameters:Total ammonia nitrogen (TAN): 1–81%; nitrite nitrogen (NO₂-N): 43–98%; nitrate nitrogen (NO₃-N): 51–75%; total Kjeldahl nitrogen (TKN): 45–61%; total phosphorus (TP): 59–84%; biochemical oxygen demand (BOD): 37–67%; total suspended solids (TSS): 75–87%; volatile suspended solids (VSS): 68–91%; and settleable solids (SS): 57–100%. The best performance of the CW was observed with a 4-day HRT.

Costa-Pierce [75] developed the Integrated Aquaculture–Wetland Ecosystem (AWE). This system consisted of the polyculture of aquatic plants such as Eichhornia crassipes and Ipomea aquatica, along with hybrid tilapia (Oreochromis mossambicus × O. urolepis hornorum), common carp (Cyprinus carpio), mosquitofish (Gambusia affinis), and red swamp crayfish (Procambarus clarkii). The results indicated that Eichhornia crassipes removed approximately 90% of ammonia and nitrate nitrogen, while the wetland system provided an additional 7% removal. Overall, the AWE system achieved a 97% total reduction in inorganic nitrogen concentrations in the aquaculture effluent. In addition, the system demonstrated the potential for producing aquatic food while achieving a near-complete removal of inorganic nitrogen from wastewater.

Historical evidence shows that a variety of species have been cultivated in conjunction with CW systems, including penaeid shrimp (Penaeidae), rainbow trout (Oncorhynchus mykiss), tilapia (Oreochromis spp.), and channel catfish (Ictalurus punctatus) [76,77]. These systems have been applied to both freshwater and marine environments, using water from various sources, including groundwater and surface water [78,79].

At a commercial scale, tilapia farming has been integrated with surface flow constructed wetlands (FWS) planted with Canna spp. and Scirpus sp. This system operated at a Hydraulic Loading Rate (HLR) of 3.03 m/day with an HRT of 2.9 h, supporting stocking densities greater than 35 kg/m³. The reported removal efficiencies were as follows: TSS: 90%; NO₂-N: 91%; and NO₃-N: 76%. The addition of a sedimentation unit significantly improved the TSS removal. This highlights the importance of considering sedimentation units in future CW systems for aquaculture wastewater treatment [79].

In another study, Zachritz and Fuller [76] designed a system that successfully supported commercial-scale tilapia production with densities over 35 kg/m³. The removal efficiencies in SSF wetlands were reported as follows: TSS: 67.2; TAN: 46%; NO₂-N: 87.0%; and NO₃-N: 40.6%. The authors concluded that the optimal performance of SSF wetlands, with the simultaneous removal of TAN, NO₂-N, and NO₃-N, was achieved when TAN loading rates were below 6.0 g/m²/day. The application of CWs for agricultural wastewater treatment, including aquaculture, has been extensively studied [80,81]. While review articles have reported on the removal efficiencies of CWs in wastewater treatment, none have provided a detailed analysis of the plant species used in these systems for aquaculture applications. In

Table 1. Cultivated species under aquaculture conditions using constructed wetlands for wastewater treatment (adapted from Vimazal [49]).

Cultivated Species	Country	CW Type	HLR	HRT	Reference
Channel catfish (Ictalurus punctatus)	USA	FWS	7.7–9.1 cmd−1	1–4 d	[74]
Milkfish (Chanos chanos)	Taiwan	FWS-FH	1.8–13.5 cmd−1		[45]
Rainbow trout (Oncorhynchus mykiss)	Canada	FH	21.2 cmd−1	1.3 d	[82]
Not specified	Canada	FH	3 cmd−1	4 d	[83]
Chinook salmon (Oncorhynchus tshawytscha) Coho salmon (Oncorhynchus kisutch)	USA	FWS	7.9 cmd−1	4.2 d	[84]
Channel catfish (Ictalurus punctatus) Black carp (Megalobrama amblycephala)	China	VF	14.7–39.1 cmd−1	0.58–1.44 d	[85]
Pacific white shrimp (Litopenaeus vannamei)	Taiwan	FWS-FH	30 cmd−1	0.76 d	[46]
Rainbow trout (Oncorhynchus mykiss)	Germany	FH	1–5 md−1	1.5–7.5 d	[77]
Red tilapia (Oreochromis massambicus x Oreochromis aureus)	USA	FH	3.03 md−1	0.12 d	[79]
Rainbow trout (Oncorhynchus mykiss) Brook trout (Salvelinus fontinalis) Brown trout (Salmo trutta)	Germany	FH	10.6–28.9 md−1	0.014 d	[86]
Rainbow trout (Oncorhynchus mykiss)	Germany	FH	3.3–14.1 md−1		[87]
Channel catfish (Ictalurus punctatus)	China	VF	22.5–33.8 cmd−1	0.9–1.3 d	[88]
Pacific white shrimp (Litopenaeus vannamei)	China	VF-FH	86 cmd−1	0.76 d	[89]
Nile tilapia (Oreochromis niloticus) Common carp (Cyprinus carpio)	Vietnam	VF-FH	75–300 cmd−1		[90]

CW type abbreviations: FWS = Free Water Surface, FH = Free Horizontal Flow, and VF = Vertical Flow. Units: cm d⁻¹ (centimeters per day) and m d⁻¹ (meters per day).

, Vymazal [49] presents a review of CW applications classified by the type of aquaculture system. That review analyzed 14 articles and focused on identifying the types of wetlands, Hydraulic Loading Rates (HLRs), Hydraulic Residence Times (HRTs), and highlighted notable removal efficiencies.

Relevant data have been reported indicating that this type of treatment is both feasible and cost-effective. This has been confirmed by Chen et al. [91] in the treatment of wastewater in Vietnam and China [92]. Even though aquaculture wastewater typically exhibits low pollutant concentrations, the large volumes involved pose significant treatment challenges. Initial findings demonstrated that intensive rainbow trout (Oncorhynchus mykiss) farms produce effluents that are 20 to 25 times more diluted than medium-strength municipal wastewater. In this context, the most important components to remove are phosphorus and nutrients such as nitrogen, which are essential factors contributing to the growth of algae and other microorganisms in aquaculture wastewater [49].

The evidence indicates that fish feed is the primary source of nitrogen (N) and phosphorus (P), contributing to over 85% of potassium (K), 70% of zinc (Zn), and at least 60% of these elements present in the effluents when water exchange rates are below 100 L of the replacement water per kg of feed input. Conversely, the presence of calcium (Ca), magnesium (Mg), sulfur (S), iron (Fe), and copper (Cu) depends more on the quality and volume of the source water [93]. Excessive concentrations of these nutrients can lead to the proliferation of harmful algal blooms in surface waters [94,95] and contribute to nutrient pollution in groundwater [96,97].

It is important to note the diversity of species studied in these systems, including Tilapia spp., Oncorhynchus mykiss, Ictalurus punctatus, and Litopenaeus vannamei. Design parameters for these systems suggest that Hydraulic Residence Times (HRTs) for nutrient removal in aquaculture wastewater can vary from as low as 0.014 days but generally do not exceed 5 days [83,84]. Hydraulic Loading Rates (HLRs), on the other hand, vary widely depending on the system configuration, the biomass load, the study period, and the age of the cultured organisms. This information suggests that, regardless of the type of the constructed wetland (CW) configuration employed, the HLR and HRT are the most critical variables to ensure a proper hydraulic performance and effective nutrient removal. However, the vegetation and substrate play fundamental roles in treatment efficiency [98]. Therefore, in the following section we analyze these components in greater detail.

3.2. Empirical Evidence on the Treatment of Aquaculture Wastewater Using Constructed Wetlands

Table 2 presents the compiled and harmonized information on the study variables reviewed in this work. In accordance with the research objectives, the table summarizes the country where each study was conducted, the aquaculture species cultivated, the type of vegetation used in the constructed wetland (CW), and the classification of the plant species (emergent or floating), as these are the most used types. The analysis also considered whether the study incorporated a recirculating aquaculture system (RAS) integrated with the wetland for water reuse purposes. Additionally, the research scale was recorded as an important variable to assess the technological maturity of CWs for aquaculture wastewater treatment [99]. This compilation provides an overview of current design trends for wetlands treating aquaculture wastewater and highlights potential areas for future research at both laboratory and commercial scales worldwide.

3.3. Research by Country on the Treatment of Aquaculture Wastewater Using Constructed Wetlands

Table 2 presents the findings of the reviewed studies, where it is evident that the application of constructed wetlands (CWs) in aquaculture is a growing field of research. Empirical investigations have been conducted in 19 countries, with China leading the number of studies, representing 33% of the total sample. This predominance may be attributed to China being the world’s largest producer of aquaculture products, contributing 36% of the total global aquaculture production [4].

In Brazil, the studies identified accounted for 15.5% of the total sample. This country’s interest in aquaculture wastewater treatment research can be associated with its position as the third-largest aquaculture producer in the Americas, following Chile and Ecuador [100]. Aquaculture represents 83.5% of Brazil’s total fish production, with Nile tilapia (Oreochromis niloticus) constituting 63.9% of the country’s aquaculture output.

The United States’ research represented 10% of the reviewed sample. Multiple factors may be driving the interest in this area, such as the country’s status as the world’s largest importer of aquaculture products [4]. The domestic supply from its 5961 fish farms remains insufficient to meet the demand. Moreover, the availability of significant research funding supports investigations into aquaculture development and wastewater management [101]. Recently, geographical areas with potential for commercial aquaculture have been identified in the U.S., based on analyses of environmental, social, and economic factors [102], reflecting a growing interest in expanding the aquaculture sector.

Additionally, 16 other countries have conducted research on the use of CWs in aquaculture. Germany, despite being a landlocked European country, accounted for 6.6% of the studies. This is noteworthy since Germany has been conducting CW research since the 1950s [103]. Excluding China, Asian countries—known for their strong presence in aquaculture—contributed 15.5% of the CW research for aquaculture wastewater treatment. This finding aligns with data indicating that Asian countries produce 70% of the world’s total aquatic animal output [13].

3.4. Aquaculture Species Reported in Constructed Wetlands Wastewater Treatment Studies

Regarding the aquaculture species reported in the reviewed literature (Table 2), there is a clear trend that reflects the most farmed species under controlled conditions worldwide. As shown in Figure 2, Nile tilapia (Oreochromis niloticus) was the most frequently studied species, appearing in 22.2% of the research reviewed. When combined with studies on blue tilapia (Oreochromis aureus) and Mozambique tilapia (Oreochromis mossambicus), tilapia species collectively represented 27.78% of the studies. As the second most important cultured fish species globally, tilapia is extremely popular among aquaculture producers; consequently, the adoption of innovative technologies for its sustainable cultivation is significant [104].

The Pacific white shrimp (Litopenaeus vannamei) accounted for 16.6% of the CW studies. This may be due to L. vannamei dominating global shrimp production and being exported to numerous international markets. This species holds a leading position due to its growing global demand and competitive pricing [105]. Shrimp products, classified as high-value aquaculture commodities, are projected to reach a global production volume of 7.28 million metric tons by 2025, with a compound annual growth rate (CAGR) of 6.1% from 2020 to 2026 [106]. Therefore, the development of alternative wastewater treatment systems for shrimp aquaculture is critical for its sustainable growth.

Channel catfish (Ictalurus punctatus) represented 11.1% of the reviewed research. Native to the United States, Canada, and northeastern Mexico, this freshwater species has significant economic potential, as evidenced by the increasing global production [107]. Its favorable traits make it attractive for commercial filet production, and it remains a major aquaculture species in the United States, accounting for more than 60% of the country’s total aquaculture output [108,109]. Additionally, studies were identified involving yellow catfish (Tachysurus fulvidraco), which together accounted for 19.44% of the studies—surpassing the percentage observed for L. vannamei. This highlights the importance of developing wastewater treatment systems tailored for catfish species, which, although less economically dominant than shrimp or tilapia, are nonetheless significant for global aquaculture production.

Common carp (Cyprinus carpio) studies represented 5.56% of the reviewed literature. Despite this relatively low percentage, the global production of common carp exceeds 4.1 million metric tons [4]. Furthermore, other carp species identified in the reviewed studies include Megalobrama amblycephala, Hypophthalmichthys molitrix, Mylopharyngodon piceus, and Carassius gibelio, which collectively accounted for 11.11% of the CW research related to aquaculture wastewater treatment. This finding emphasizes their global relevance and the need for further research focused on improving wastewater management in carp aquaculture.

Table 2. The empirical evidence of vegetation used in constructed wetlands for the treatment of aquaculture wastewater.

Country	Aquaculture Species Cultivated	Vegetation	Type of Plant in the Wetlands	RAS	Study Scale	Reference
Taiwan	Milkfish (Chanos chanos).	Ipomoea aquatica, Paspalum vaginatum, and Phragmites australis	Emergent and Floating plants	Not included	HP	[45]
Taiwan	Pacific white shrimp (Litopenaeus vannamei).	Phragmites australis	Emergent plant	Included	LB	[46]
China	Pacific white shrimp (Litopenaeus vannamei).	Phragmites australis, smooth cordgrass (Spartina alterniflora Loisel), and scirpus (Scirpus mariqueter)	Emergent plant	Included	LB	[50]
China	NE	Sesuvium portulacastrum	Emergent plant	Not included	LB	[51]
China	Perch American (Micropterus salmoides).	Canna indica, Thalia Dealbata, and Iris germanica	Emergent plant	Not included	LB	[52]
China	Nile tilapia (Oreochromis niloticus).	Pontederia, Arundo, and Iris germanica.	NE	Not included	LB	[64]
E.E.U.U.	Channel catfish (Ictalurus punctatus).	Scirpus californicus, Zizaniopsis, miliacea, and Panicurn hemitomon	Floating plant	Included	LB	[74]
E.E.U.U.	Hybrid tilapia (Oreochromis mossambicus × O. urolepis hornorum common carp (Cyprinus carpio), mosquitofish (Gambusia affinis), and red swamp crayfish (Procambarus clarkii	Eichhornia crassipes and Ipomea aquatica	Floating plant	Not included	LB	[75]
E.E.U.U.	Nile tilapia (Oreochromis niloticus).	Canna Lillies (Canna sp.) and bulrush (Scirpus sp.)	Emergent plant	Included	LB	[76]
Germany	Rainbow trout (Oncorhynchus mykiss).	Phragmites australis	Emergent plant	Not included	LB	[77]
Australia	Rainbow trout (Oncorhynchus mykiss	Juncus kraussii	Emergent plant	Not included	LB	[78]
E.E.U.U.	Red tilapia (O. mossambicus O. aureus).	Typha sp. and Canna Lillies.	Emergent plant	Included	LB	[79]
Canada	Rainbow trout (Oncorhynchus mykiss).	Phragmites australis and Typha latifolia	Emergent plant	Not included	LB	[82]
Canada	Atlantic salmon (Salmo salar)	Phragmites communis and Typha latifolia	Emergent plant	Included	LB	[83]
E.E.U.U.	Royal salmon (Oncorhynchus tsawytscha).	NE	NE	Not included	LB	[84]
Germany	Rainbow trout (Oncorhynchus mykiss).	Phragmites australis	Emergent plant	Not included	LB	[86]
Germany	Rainbow trout (Oncorhynchus mykiss).	Phragmites communis and Phalaris arundinacea	Emergent plant	NE	LB	[87]
China	Channel catfish (Ictalurus punctatus).	NE	NE	Included	LB	[88]
China	Pacific white shrimp (Litopenaeus vannamei).	NE	NE	Included	LB	[89]
Vietnam	Nile tilapia (Oreochromis niloticus) and common carp (Cyprinus carpio).	Canna generalis	Emergent plant	Included	LB	[90]
China	Chinese carp (Ctenopharyngodon idella).	Nymphaea alba, Myriophyllum sp., and Vallisneria natans	Emergent and Floating plants	Included	LB	[110]
China	Giant river prawn (Macrobrachium rosenbergii).	Typha angustifolia and Canna indica	Emergent plant	Included	LB	[111]
Denmark	Rainbow trout (Oncorhynchus mykiss).	NE	NE	NE	LB	[112]
China	Channel catfish (Ictalurus punctatus), spiny barb (Spinibarbus sinensis), and yellow catfish (Pelteobagrus fulvidraco).	Canna indica, Iris tectorum, Acorus calamus, Cyperus papiro, and Thalia dealbata	Emergent plant	Included	LB	[113]
Israel	NE	Salicornia	Emergent plant	Included	LB	[114]
China	NE	Thalia dealbata, Arundo Donax, Iris versicolor, Phragmites australis, Myriophyllum spicatum, and Nymphaea alba	Emergent and Floating plants	Not included	LB	[115]
Finland	NE	Salicornia europaea and Phragmites australis	Emergent plant	Included	LB	[116]
China	Pacific white shrimp (Litopenaeus vannamei).	Phragmites australis, Spartina alterniflora Loisel, and Scirpus mariqueter	Emergent plant	Not included	LB	[117]
Brazil	Pacific white shrimp (Litopeneaus vannamei).	Spartina alterniflora	Floating plant	Included	LB	[118]
Brazil	Nile tilapia (Oreochromis niloticus).	Salvinia sp. and Eichhornia crassipes.	Floating plant	Not included	LB	[119]
Brazil	Nile tilapia (Oreochromis niloticus).	Eichhornia crassipes	Floating plant	Included	LB	[120]
Malaysia	Channel catfish (Ictalurus punctatus).	Eichhornia crassipes and Limnocharis flava	Floating plant	Not included	LB	[121]
Colombia	Channel catfish (Ictalurus punctatus).	Eichhornia crassipes	Floating plant	Not included	LB	[122]
Brazil	River shrimp (Macrobrachium amazonicum).	Eichhornia crassipes and Pistia stratiotes	Floating plant	Not included	LB	[123]
Brazil	Nile tilapia (Oreochromis niloticus).	Eichhornia crassipes, Pistia stratiotes, and Salvinia molesta	Floating plant	Not included	LB	[124]
Brazil	Nile tilapia (Oreochromis niloticus) and	NE	NE	Included	LB	[125]
Hungary	silver Carp (Hypophthalmichthys molitrix). Common carp (Cyprinus carpio), and sharp tooth catfish (Clarias gariepenus).	Phragmites australis, Typha angustifolia, Lemna minor, and Typha latifolia	Emergent and Floating plants	Not included	LB	[126]
Hungary	Sharp tooth catfish (Clarias gariepinus), Nile tilapia (Oreochromis niloticus), common carp (Cyprinus carpio),	NE	NE	Included	LB	[127]
Hungary	Sharp tooth catfish (Clarias gariepinus). Common carp (Cyprinus carpio) and Nile tilapia (Oreochromis niloticus).	Phragmites australis, Typha latifolia, Typha angustifolia, Salix viminalis, and Arundo donax	Emergent plant	Included	LB	[128]
China	Puffer fish (Dichotomyctere ocellatus).	Phragmites australis, Spartina alterniflora, and Scirpus mariqueter	Emergent plant	Included	LB	[129]
China	Channel catfish (Ictalurus punctatuss) Brema Wuchang (Megalobrama amblycephala), silver carp (Hypophthalmichthys Molitri), and black carp (Mylopharyngodon Piceus).	Canna indica, Typha latifolia, Acorus calamus, and Agave sisalana	Emergent plant	Included	ER	[130]
China	Chinese carp (Ctenopharyngodon idella).	Nymphaea alba L, Myriophyllum sp., and Vallisneria natans	Floating plant	Included	LB	[131]
Mexico	NE	Arundo donax, Medicago sativa, and Zandechia aethiopica	Emergent plant	Not included	LB	[132]
China	NE	Thalia dealbata, Arundo, donax, Phragmites australis, Myriophyllum spicatum, and Nymphaea alba	Emergent plant	Not included	LB	[133]
China	Channel catfish (Ictalurus punctatuss).	Canna indica, Typha orientalis, and Acorus calamus	Emergent plant	Included	LB	[134]
Italy	Sea bass (Dicentrarchus labrax), and sea bream (Sparus aurata).	Ulva Linnaeus	NE	Not included	HP	[135]
E.E.U.U.	Pacific white shrimp (Litopenaeus vannamei).	NE	NE	NE	LB	[136]
Israel	NE	Salicornia persica	NE	Included	LB	[137]
Germany	NE	Salicornia europaea and Tripolium pannonicum	NE	Included	LB	[138]
E.E.U.U.	Pacific white shrimp (Litopenaeus vannamei).	Gracilaria tikvahiae	Floating plant	Not included	LB	[139]
China	Milkfish (Chanos chanos).	Paspalum vaginatum, Ipomoea aquatica, and Phragmites australis	Floating plant	Not included	HP	[140]
Taiwan	Pacific white shrimp (Litopenaeus vannamei).	Pistia stratiotes, Typha angustifolia, Phragmites common, Canna generalis, and Cyperus alternifa	Emergent plant	Not included	LB	[141]
E.E.U.U.	Channel catfish (Ictalurus punctatus).	Scirpus californicus, Zizaniopsis miliacea, and Panicurn hemitomon	Emergent plant	Not included	LB	[142]
China	Channel catfish (Ictalurus punctatus).	NE	NE	Not included	LB	[143]
Hungary	NE	Phragmites Australis, Typha latifolia angustifolia, Salix viminalis, Arundo donax, and Tamarix tetrandra	Emergent plant	Not included	HP	[144]
Malaysia	NE	Eichhornia crassipes and Limnocharis flava	NE	Not included	LB	[145]
China	NE	Thalia dealbata, Canna indica, and Phragmites australis	NE	Not included	LB	[146]
Brazil	Nile tilapia (Oreochromis niloticus).	Eichhornia crassipes, Pistia stratiotes, and Salvínia molesta	Floating plant	Not included	LB	[147]
E.E.U.U.	Red tilapia (O. mossambicus x O. aureus).	Canna sp. and Scirpus sp.	Emergent plant	Included	LB	[148]
Thailand	Nile tilapia (Oreochromis niloticus).	NE	NE	Included	LB	[149]
Brazil	Tambaqui (Colossoma macropomum).	Lactuca sativa spp.	Emergent plant	Not included	LB	[150]
Brazil	Nile tilapia (Oreochromis niloticus).	Typha latifolia	Emergent plant	Included	LB	[151]
Indonesia	Pacific white shrimp (Litopenaeus vannamei).	NE	NE	Not included	LB	[152]
Indonesia	Claria (Clarias gariepinus).	Chrysopogon zizanioides, Cyperus alternifolius, and Eichhornia crassipes	Emergent plant	Not included	LB	[153]
Indonesia	Pacific white shrimp (Litopenaeus vannamei).	Chrysopogon zizanioides	Emergent plant	Not included	LB	[154]
Indonesia	NE	Chrysopogon zizanioides	Emergent plant	Not included	LB	[155]
Chile	Jaks (Carangidae).	Agarophyton chilense, Mazzaella canaliculate, and Ulva lactuca	Floating plant	Not included	LB	[156]
China	Nile tilapia (Oreochromis niloticus).	Chlorella sp.	Floating plant	Included	LB	[157]
China	Tachysurus fulvidraco and Lateo labrax japonicas.	Phragmites australis, Phalaris arundinacea, Acorus calamus, Typha latifolia, Scirpus lacustris, and Iris pseudacorus	Emergent plant	Not included	LB	[158]
China	NE	Phragmites australis	Emergent plant	Not included	LB	[159]

Nomenclature: RAS: Integrated into recirculating aquaculture system, LB: Laboratory scale, HP: Pilot scale, ER: Real scale, NE: Not specified.

Table 2. The empirical evidence of vegetation used in constructed wetlands for the treatment of aquaculture wastewater.

Country	Aquaculture Species Cultivated	Vegetation	Type of Plant in the Wetlands	RAS	Study Scale	Reference
Taiwan	Milkfish (Chanos chanos).	Ipomoea aquatica, Paspalum vaginatum, and Phragmites australis	Emergent and Floating plants	Not included	HP	[45]
Taiwan	Pacific white shrimp (Litopenaeus vannamei).	Phragmites australis	Emergent plant	Included	LB	[46]
China	Pacific white shrimp (Litopenaeus vannamei).	Phragmites australis, smooth cordgrass (Spartina alterniflora Loisel), and scirpus (Scirpus mariqueter)	Emergent plant	Included	LB	[50]
China	NE	Sesuvium portulacastrum	Emergent plant	Not included	LB	[51]
China	Perch American (Micropterus salmoides).	Canna indica, Thalia Dealbata, and Iris germanica	Emergent plant	Not included	LB	[52]
China	Nile tilapia (Oreochromis niloticus).	Pontederia, Arundo, and Iris germanica.	NE	Not included	LB	[64]
E.E.U.U.	Channel catfish (Ictalurus punctatus).	Scirpus californicus, Zizaniopsis, miliacea, and Panicurn hemitomon	Floating plant	Included	LB	[74]
E.E.U.U.	Hybrid tilapia (Oreochromis mossambicus × O. urolepis hornorum common carp (Cyprinus carpio), mosquitofish (Gambusia affinis), and red swamp crayfish (Procambarus clarkii	Eichhornia crassipes and Ipomea aquatica	Floating plant	Not included	LB	[75]
E.E.U.U.	Nile tilapia (Oreochromis niloticus).	Canna Lillies (Canna sp.) and bulrush (Scirpus sp.)	Emergent plant	Included	LB	[76]
Germany	Rainbow trout (Oncorhynchus mykiss).	Phragmites australis	Emergent plant	Not included	LB	[77]
Australia	Rainbow trout (Oncorhynchus mykiss	Juncus kraussii	Emergent plant	Not included	LB	[78]
E.E.U.U.	Red tilapia (O. mossambicus O. aureus).	Typha sp. and Canna Lillies.	Emergent plant	Included	LB	[79]
Canada	Rainbow trout (Oncorhynchus mykiss).	Phragmites australis and Typha latifolia	Emergent plant	Not included	LB	[82]
Canada	Atlantic salmon (Salmo salar)	Phragmites communis and Typha latifolia	Emergent plant	Included	LB	[83]
E.E.U.U.	Royal salmon (Oncorhynchus tsawytscha).	NE	NE	Not included	LB	[84]
Germany	Rainbow trout (Oncorhynchus mykiss).	Phragmites australis	Emergent plant	Not included	LB	[86]
Germany	Rainbow trout (Oncorhynchus mykiss).	Phragmites communis and Phalaris arundinacea	Emergent plant	NE	LB	[87]
China	Channel catfish (Ictalurus punctatus).	NE	NE	Included	LB	[88]
China	Pacific white shrimp (Litopenaeus vannamei).	NE	NE	Included	LB	[89]
Vietnam	Nile tilapia (Oreochromis niloticus) and common carp (Cyprinus carpio).	Canna generalis	Emergent plant	Included	LB	[90]
China	Chinese carp (Ctenopharyngodon idella).	Nymphaea alba, Myriophyllum sp., and Vallisneria natans	Emergent and Floating plants	Included	LB	[110]
China	Giant river prawn (Macrobrachium rosenbergii).	Typha angustifolia and Canna indica	Emergent plant	Included	LB	[111]
Denmark	Rainbow trout (Oncorhynchus mykiss).	NE	NE	NE	LB	[112]
China	Channel catfish (Ictalurus punctatus), spiny barb (Spinibarbus sinensis), and yellow catfish (Pelteobagrus fulvidraco).	Canna indica, Iris tectorum, Acorus calamus, Cyperus papiro, and Thalia dealbata	Emergent plant	Included	LB	[113]
Israel	NE	Salicornia	Emergent plant	Included	LB	[114]
China	NE	Thalia dealbata, Arundo Donax, Iris versicolor, Phragmites australis, Myriophyllum spicatum, and Nymphaea alba	Emergent and Floating plants	Not included	LB	[115]
Finland	NE	Salicornia europaea and Phragmites australis	Emergent plant	Included	LB	[116]
China	Pacific white shrimp (Litopenaeus vannamei).	Phragmites australis, Spartina alterniflora Loisel, and Scirpus mariqueter	Emergent plant	Not included	LB	[117]
Brazil	Pacific white shrimp (Litopeneaus vannamei).	Spartina alterniflora	Floating plant	Included	LB	[118]
Brazil	Nile tilapia (Oreochromis niloticus).	Salvinia sp. and Eichhornia crassipes.	Floating plant	Not included	LB	[119]
Brazil	Nile tilapia (Oreochromis niloticus).	Eichhornia crassipes	Floating plant	Included	LB	[120]
Malaysia	Channel catfish (Ictalurus punctatus).	Eichhornia crassipes and Limnocharis flava	Floating plant	Not included	LB	[121]
Colombia	Channel catfish (Ictalurus punctatus).	Eichhornia crassipes	Floating plant	Not included	LB	[122]
Brazil	River shrimp (Macrobrachium amazonicum).	Eichhornia crassipes and Pistia stratiotes	Floating plant	Not included	LB	[123]
Brazil	Nile tilapia (Oreochromis niloticus).	Eichhornia crassipes, Pistia stratiotes, and Salvinia molesta	Floating plant	Not included	LB	[124]
Brazil	Nile tilapia (Oreochromis niloticus) and	NE	NE	Included	LB	[125]
Hungary	silver Carp (Hypophthalmichthys molitrix). Common carp (Cyprinus carpio), and sharp tooth catfish (Clarias gariepenus).	Phragmites australis, Typha angustifolia, Lemna minor, and Typha latifolia	Emergent and Floating plants	Not included	LB	[126]
Hungary	Sharp tooth catfish (Clarias gariepinus), Nile tilapia (Oreochromis niloticus), common carp (Cyprinus carpio),	NE	NE	Included	LB	[127]
Hungary	Sharp tooth catfish (Clarias gariepinus). Common carp (Cyprinus carpio) and Nile tilapia (Oreochromis niloticus).	Phragmites australis, Typha latifolia, Typha angustifolia, Salix viminalis, and Arundo donax	Emergent plant	Included	LB	[128]
China	Puffer fish (Dichotomyctere ocellatus).	Phragmites australis, Spartina alterniflora, and Scirpus mariqueter	Emergent plant	Included	LB	[129]
China	Channel catfish (Ictalurus punctatuss) Brema Wuchang (Megalobrama amblycephala), silver carp (Hypophthalmichthys Molitri), and black carp (Mylopharyngodon Piceus).	Canna indica, Typha latifolia, Acorus calamus, and Agave sisalana	Emergent plant	Included	ER	[130]
China	Chinese carp (Ctenopharyngodon idella).	Nymphaea alba L, Myriophyllum sp., and Vallisneria natans	Floating plant	Included	LB	[131]
Mexico	NE	Arundo donax, Medicago sativa, and Zandechia aethiopica	Emergent plant	Not included	LB	[132]
China	NE	Thalia dealbata, Arundo, donax, Phragmites australis, Myriophyllum spicatum, and Nymphaea alba	Emergent plant	Not included	LB	[133]
China	Channel catfish (Ictalurus punctatuss).	Canna indica, Typha orientalis, and Acorus calamus	Emergent plant	Included	LB	[134]
Italy	Sea bass (Dicentrarchus labrax), and sea bream (Sparus aurata).	Ulva Linnaeus	NE	Not included	HP	[135]
E.E.U.U.	Pacific white shrimp (Litopenaeus vannamei).	NE	NE	NE	LB	[136]
Israel	NE	Salicornia persica	NE	Included	LB	[137]
Germany	NE	Salicornia europaea and Tripolium pannonicum	NE	Included	LB	[138]
E.E.U.U.	Pacific white shrimp (Litopenaeus vannamei).	Gracilaria tikvahiae	Floating plant	Not included	LB	[139]
China	Milkfish (Chanos chanos).	Paspalum vaginatum, Ipomoea aquatica, and Phragmites australis	Floating plant	Not included	HP	[140]
Taiwan	Pacific white shrimp (Litopenaeus vannamei).	Pistia stratiotes, Typha angustifolia, Phragmites common, Canna generalis, and Cyperus alternifa	Emergent plant	Not included	LB	[141]
E.E.U.U.	Channel catfish (Ictalurus punctatus).	Scirpus californicus, Zizaniopsis miliacea, and Panicurn hemitomon	Emergent plant	Not included	LB	[142]
China	Channel catfish (Ictalurus punctatus).	NE	NE	Not included	LB	[143]
Hungary	NE	Phragmites Australis, Typha latifolia angustifolia, Salix viminalis, Arundo donax, and Tamarix tetrandra	Emergent plant	Not included	HP	[144]
Malaysia	NE	Eichhornia crassipes and Limnocharis flava	NE	Not included	LB	[145]
China	NE	Thalia dealbata, Canna indica, and Phragmites australis	NE	Not included	LB	[146]
Brazil	Nile tilapia (Oreochromis niloticus).	Eichhornia crassipes, Pistia stratiotes, and Salvínia molesta	Floating plant	Not included	LB	[147]
E.E.U.U.	Red tilapia (O. mossambicus x O. aureus).	Canna sp. and Scirpus sp.	Emergent plant	Included	LB	[148]
Thailand	Nile tilapia (Oreochromis niloticus).	NE	NE	Included	LB	[149]
Brazil	Tambaqui (Colossoma macropomum).	Lactuca sativa spp.	Emergent plant	Not included	LB	[150]
Brazil	Nile tilapia (Oreochromis niloticus).	Typha latifolia	Emergent plant	Included	LB	[151]
Indonesia	Pacific white shrimp (Litopenaeus vannamei).	NE	NE	Not included	LB	[152]
Indonesia	Claria (Clarias gariepinus).	Chrysopogon zizanioides, Cyperus alternifolius, and Eichhornia crassipes	Emergent plant	Not included	LB	[153]
Indonesia	Pacific white shrimp (Litopenaeus vannamei).	Chrysopogon zizanioides	Emergent plant	Not included	LB	[154]
Indonesia	NE	Chrysopogon zizanioides	Emergent plant	Not included	LB	[155]
Chile	Jaks (Carangidae).	Agarophyton chilense, Mazzaella canaliculate, and Ulva lactuca	Floating plant	Not included	LB	[156]
China	Nile tilapia (Oreochromis niloticus).	Chlorella sp.	Floating plant	Included	LB	[157]
China	Tachysurus fulvidraco and Lateo labrax japonicas.	Phragmites australis, Phalaris arundinacea, Acorus calamus, Typha latifolia, Scirpus lacustris, and Iris pseudacorus	Emergent plant	Not included	LB	[158]
China	NE	Phragmites australis	Emergent plant	Not included	LB	[159]

Nomenclature: RAS: Integrated into recirculating aquaculture system, LB: Laboratory scale, HP: Pilot scale, ER: Real scale, NE: Not specified.

In total, wastewater from 25 species was studied, including some of the most popular species worldwide (Figure 3). Research has predominantly focused on the two most widely farmed species: tilapia (Oreochromis niloticus) and shrimp (Litopenaeus vannamei). However, very localized species have also been studied using constructed wetland (CW) technologies for wastewater treatment. This limited information highlights the importance of further research, as attention should not only be paid to the most popular species. Other freshwater and marine species also need to be studied, considering that in 2022 the most commercially traded aquatic animal products were finfish (65% of total value), crustaceans (23%), and mollusks and other aquatic invertebrates (11%). Salmonids were the most valuable group commercially (20% in terms of value), followed by shrimp and prawns (17%) [4]. Nevertheless, there were 448 aquaculture species farmed in 197 countries, many of which have not yet been studied [13]. In this context, only 17% of aquaculture species were found in the present study, revealing a significant knowledge gap for future research.

3.5. Plant Species Utilized in Constructed Wetlands for Aquaculture Wastewater Treatment

Existing literature reviews that compile broad information regarding the use of plants in CW for aquaculture wastewater remediation are scarce. From Scopus, 10 review articles were analyzed that explore the biological treatment of wastewater. Jin et al. [160] describes the development status and research trends in biofiltration, mentioning that this type of treatment is used as a secondary treatment, particularly for the removal of micro-contaminants through oxidation technologies and constructed wetlands on aquaculture farms. Gorito et al. [63] concluded that the removal of organic micro-contaminants using CWs is a recent area of study, requiring further research to determine the feasibility of large-scale applications. Although its potential is recognized, specific information for aquaculture remains limited.

Local context reviews, such as in Thailand, state that only 5% of aquaculture wastewater is treated in conventional plants, and only one CW system has been implemented at a real scale for domestic wastewater treatment [161]. Their national review highlights the urgent need to reuse wastewater for agricultural purposes, despite Thailand being one of Asia’s main aquaculture producers, with 1,000,181 tons [162]. On the other hand, Kurniawan et al. [163] affirm that aquaculture in Malaysia is still linked to environmental problems, despite its many benefits. They analyzed 11 articles demonstrating the effectiveness and feasibility of using CWs for the treatment of these effluents and proposed CWs as a clean production alternative using floating plants as a secondary treatment.

Wu and Song [164] emphasize that the treatment and disposal of solid aquaculture waste has attracted wide attention. They highlight the following technologies for its treatment: constructed wetlands, aerobic composting, anaerobic treatment, enzymatic or chemical hydrolysis, and aquaponics. Tom et al. [62] found that RAS technologies integrated with constructed wetlands are gaining increasing importance, as they have proven to be a viable and cost-effective method for wastewater treatment. However, they only describe the technologies without detailing essential elements in their operational characteristics, which is limited to seven studies analyzed.

Henares et al. [36] highlight CWs as a biological treatment method, describing their operation and important elements regarding vegetation, such as the use of emergent vegetation, rooted floating-leaf plants, submerged plants, and free-floating plants. Additionally, they emphasize that for proper operation, it is necessary to periodically remove part of the biomass to allow macrophytes to grow and maintain high nutrient uptake rates. They briefly analyzed removal rates and confirmed the possibility of using this biomass as fish feed. They reviewed six articles: three with emergent plants and three with free-floating plants. Henares et al. [36] agree with Gorito et al. [63] on the scarcity of scientific publications concerning the aquaculture industry, particularly regarding its global supply and demand, its environmental impacts due to effluent generation, and the treatment technologies currently available for aquaculture effluents. In terms of design, Messer et al. [165] conclude that it is vital to include basic performance parameters for wetlands, such as the influent and effluent concentrations, hydraulic retention time, Hydraulic Loading Rate, and plant species.

Emergent and Floating Plant Species Used in CW for Aquaculture Wastewater Treatment

Initial statistical data indicate that 10.06% of studies do not report the type of plant species used, corresponding to a total of 17 works. This is a notable aspect, as it represents an essential component of constructed wetlands studies. For this reason, an analysis was conducted on emergent and floating plants used in CWs and aquaculture, revealing a total of 169 plant species across 70 studies, of which 58.97% were floating plants and 41% were emergent. Figure 4 presents a Pareto diagram, showing a significant knowledge gap and potential future research lines. The data reveal frequency and percentage counts of the emergent and floating plant variables. This diagram is based on the 80/20 rule applied in quality engineering [166,167], but in this case, it indicates that 34 plant species represent 80% of the research addressed, out of the 169 plant species found. This is due to several studies using one plant or combinations of plants in their methodology, across the 70 articles analyzed.

These findings suggest that researchers in this field have primarily focused on other types of wastewaters, such as industrial, municipal, and rural wastewater [168,169]. However, aquaculture wastewater is of vital importance [170]. Based on the available empirical evidence, it is recommended that wastewater treatment in aquaculture using constructed wetlands should be investigated with greater interest, due to the urgent need arising from water scarcity and the high demand for water required by this activity. Additionally, there is a knowledge gap regarding plants with potential for study and application beyond those presented here, such as ornamental plants [171], which could offer an esthetic improvement to the landscape of production farms [172].

As shown in Figure 4, Phragmites australis was identified as the most frequently studied plant species, representing 11.2% of the reviewed cases involving constructed wetlands (CWs) for aquaculture wastewater treatment. This perennial species is notable for its tolerance to a wide range of environmental conditions, primarily due to its extensive rhizome system, which can reach depths of 60 cm to 1 m. It features rigid stems with hollow internodes and varies in height from 0.5 m to 4–5 m. Its primary mode of propagation is through rhizomes, as its seed viability is very low [67].

In second place is Typha spp., widely used in CWs and accounting for 9.47% of the studies analyzed. Within this group, Typha latifolia (4.14%) and Typha angustifolia (5.33%) are the most employed species. Like Phragmites australis, these are erect perennial rhizomatous plants that can reach heights greater than 4 m. They possess an extensive rhizome system, and their leaves are flattened or slightly rounded on the underside, with spongy basal portions. Typha species prefer soils rich in organic matter and stagnant water conditions, although specific species within the genus may tolerate different water depths. T. latifolia L., commonly known as broadleaf cattail, is the most frequently used species in CWs due to its well-documented effectiveness in aquaculture wastewater treatment. Its adaptability to environments with a high organic matter content and the suitable depths found in CW systems support its widespread application [67].

The third most frequently used species was Canna indica, found in 5.92% of the reviewed studies. This perennial herb, belonging to the Cannaceae family and native to the Americas, produces ornamental flowers and has applications in landscaping, wastewater clarification, medicine, and human consumption. Canna indica is considered an ornamental plant with valuable phytoremediation attributes, such as a rapid growth, a tolerance to adverse climatic conditions, a high capacity for contaminant accumulation, and an extensive fibrous root system. Additionally, this species enhances the aerobic conditions within the CW, thereby improving the treatment efficiency [173,174].

In fourth place, Eichhornia crassipes, commonly known as water hyacinth, was utilized in 5.3% of the studies. This free-floating perennial aquatic plant, part of the Pontederiaceae family, forms dense mats on water surfaces or mud substrates. It thrives in freshwater ponds, canals, marshes, and lakes and propagates mainly through vegetative reproduction, allowing it to rapidly colonize large areas. Eichhornia crassipes is considered one of the most efficient aquatic plants for wastewater purification, as it can remove a wide range of contaminants, including heavy metals, organic substances, and nutrients such as nitrate, ammonium, and phosphorus. It is also effective in reducing total solids in municipal, industrial (e.g., textile, metallurgical, pharmaceutical, and paper mill), domestic, and sewage wastewater [175]. Its widespread use in CWs for contaminant removal is well-documented [176].

Finally, Arundo donax, commonly known as the giant reed, was reported in several studies. This grass species from the Poaceae family—believed to have originated in Asia and later spread to the Mediterranean region, North Africa, and the Americas—is one of the world’s largest herbaceous plants. Its stems can reach heights of 8 to 10 m with a diameter of 3 to 4 cm, while its roots may extend up to 5 m deep. The leaves are long and lance-shaped, measuring up to 1 m. Research has shown that its rhizome fragments maintain 100% viability even after prolonged submersion treatments. Furthermore, such flooding treatments have been associated with the highest biomass production in both shoots and roots, highlighting the giant reed’s exceptional tolerance to waterlogging. These characteristics make Arundo donax particularly suitable for the bioremediation of wastewater [177].

3.6. Constructed Wetlands Integrated into Recirculating Aquaculture Systems (RAS)

Recirculating aquaculture systems (RAS) have been developed as an intensive, efficient, safe, and environmentally friendly approach to fish production, significantly reducing water and land use [178]. These systems aim to conserve resources while maintaining a high productivity [179]. RAS ensure the optimal development of farmed species by filtering and degrading aquaculture wastewater contaminants, recycling water, and minimizing the consumption of natural resources [85]. RAS are designed as closed-loop systems with minimal water exchange, where aquaculture wastewater undergoes filtration and aeration treatments, allowing water reuse within the system. This reduces freshwater consumption and supports intensive land-based aquaculture operations, typically conducted indoors, thus providing a controlled, high-quality environment for fish survival while significantly lowering water usage [85].

The integration of compatible technologies reflects a growing trend toward innovative biological systems and technologies within aquaculture. However, such implementations often involve high costs [53]. In this context, the present study identifies research that has integrated RAS with constructed wetlands (CWs) by country, as shown in

Table 3. Studies on RAS integrated with constructed wetlands in aquaculture.

Country	Quantity	%
China	12	17.1
Brazil	4	5.7
USA	2	2.9
Taiwan	2	2.9
Israel	2	2.9
Hungary	2	2.9
Canada	1	1.4
Vietnam	1	1.4
Finland	1	1.4
Germany	1	1.4
Studies with RAS systems	28	40%
Studies without RAS systems	42	60%

. Among the studies analyzed, 40% reported water reuse as a key objective—an essential aspect in sustainable aquaculture. Nevertheless, a major limitation of RAS–CW integrated systems lies in the need for continuous operation. The Hydraulic Loading Rates (HLRs) in CWs make it challenging to achieve uninterrupted processes [180]. Despite these operational challenges, some case studies have successfully demonstrated the application of integrated RAS–CW systems [46,48,74,83,88,89,90].

The generally accepted classification of constructed wetlands is shown in Figure 5, where three types can be observed, along with their component parts, according to the direction of the water flow [181,182,183].

In Figure 5, surface flow constructed wetlands (1) are shown. These systems consist of shallow, exposed water bodies where plants are rooted in a substrate at the bottom. These wetlands closely resemble natural ecosystems. Horizontal subsurface flow constructed wetlands (2) consist of shallow, impermeable beds filled with a porous material. This material allows efficient water passage due to its high hydraulic conductivity, promoting the formation of biofilms on its surface. Plants grow with their roots embedded in this saturated medium. Water enters from one end, flows horizontally below the surface while interacting with the substrate and plant roots, and is finally collected at the opposite end of the system. Vertical subsurface flow constructed wetlands (3), on the other hand, usually operate under unsaturated conditions. These systems include a bed approximately one meter deep, filled with porous materials such as sand or gravel. The water treatment occurs as it percolates vertically through the medium, coming into contact with plant roots, which also contribute to drainage. Water is distributed evenly over the bed surface through a network of pressurized pipes and is then collected at the bottom via perforated drainage pipes [184].

In Figure 6, three key elements are shown: a porous filter medium, microbial communities, and vegetation. The transformation of nutrients and organic matter occurs mainly due to biofilms formed by microorganisms that develop on both the porous media and within the rhizosphere. Materials used in the medium—such as soil, sand, rock, or gravel—provide a large surface area for microbial adhesion, support plant growth, and act as filters or adsorbents for pollutants present in the water.

Plants play a crucial role: by developing roots and rhizomes, they provide a structural base for bacterial colonization and help oxygenate the zones near the roots. They also absorb nutrients such as nitrogen (N), phosphorus (P), and other essential elements primarily through their roots, which transport them internally to the stems and leaves. This process additionally supplies the carbon needed for denitrification during plant biomass decomposition, helping to retain pollutants and prevent their release from sediments.

Figure 7 shows an overview of a constructed wetland system integrated into a recirculating aquaculture system. The arrows indicate the water flow from the culture pond to the wetland system, where the water is treated and subsequently received in a treated water collection pond for its reintegration into the culture pond.

The system is composed of a culture pond (1) and an overflow sedimentation tank (2), from which the wastewater is subsequently directed to a constructed wetland system. This system includes a surface flow wetland planted with Pistia stratiotes (9), Ipomoea aquatica (10), and Eichhornia crassipes (11). In addition, it contains three horizontal subsurface flow wetlands planted with Typha latifolia (13), Colocasia esculenta (14), and Ipomoea aquatica (15). The entire recirculating system is designed for the production of Oreochromis niloticus (Nile tilapia) and for cultivating plant species that may serve as complementary food sources for both tilapia and humans, such as Colocasia esculenta and Ipomoea aquatica. The removal efficiencies reported by Delfín-Portela [180] showed the following results for each plant species are as follows: Pistia stratiotes: TDS (91.94%), PO₄³⁻ (100%), and BOD₅ (79.57%); Ipomoea aquatica: TDS (75.05%), PO₄³⁻ (100%), and BOD₅ (83.33%); Eichhornia crassipes: TDS (60.70%), PO₄³⁻ (87.5%), and BOD₅ (45.54%); Typha latifolia: TDS (55.12%), PO₄³⁻ (87.5%), and BOD₅ (77.96%); and Colocasia esculenta: TDS (54.57%), PO₄³⁻ (75.5%), and BOD₅ (45.96%).

Another aspect that has been minimally explored in the analyzed studies is agricultural production using CW systems. However, there is evidence demonstrating the feasibility of integrating CWs with agriculture through the Wetland Culture^™ method [181]. This approach is defined as a sustainable agricultural system that incorporates treatment wetlands with the dual objectives of reducing non-point source nutrient pollution and eliminating the need for synthetic fertilizers by recycling nutrients [185,186]. Additionally, Wetland Culture^™ has been successfully applied in the production of maize [185].

3.7. The Research Scale of Constructed Wetlands Applied to the Aquaculture Sector

The Technology Readiness Level (TRL) is a measurement scale used to assess the maturity level of a particular technology [187]. In Mexico, the Secretariat of Science, Humanities, Technology, and Innovation (SECHTI) evaluates each project according to the criteria defined for each TRL stage. Projects are then classified based on their research progress. Following this methodology and applying the TRL scale (which ranges from levels 1 to 9), most of the selected articles correspond to TRLs 1 to 5, as they involve experimental studies conducted at laboratory-scale, microcosm, or mesocosm levels. Pilot and full-scale studies, which involve validation and demonstration in operational environments, correspond to TRLs 6 to 9, with level 9 indicating a technology fully developed and ready for commercial deployment.

Based on this classification,

Table 4. Research scale of constructed wetlands in aquaculture.

Research Scale	Quantity	%	TRL
Laboratory	64	91.43	1 to 4
Pilot Scale	1	1.43	6 and 7
Real Scale	4	5.71	8 and 9
Not Specified	1	1.43
Total Studies Analyzed	70	100.00

summarizes the findings. For constructed wetlands applied to aquaculture wastewater treatment, studies conducted at a full scale remain limited (5.71%). The majority (91.43%) are laboratory-scale investigations (TRL 1 to 5), with only a few cases (1.43%) reported at pilot scales in relevant environments.

These findings highlight the need to continue developing research at all TRL stages, given the limited availability of full-scale implementation data in this field. Although CW technologies have been successfully tested at a full scale in other contexts, the results have often not been published, making it difficult to confirm their TRL 9 status in aquaculture applications. Additionally, several factors influence the operation and design of CWs in aquaculture. As emphasized by Vimazal et al. [99], advancing to relevant full-scale environments over extended operational periods is crucial. However, economic and funding constraints often limit these efforts.

3.8. Factors Which Affect Constructed Wetlands in Aquaculture

For its implementation, the first aspect to consider is the available space for its construction, which is generally substantial. Farms must allocate this space to receive and treat the wastewater [53].

Additionally, the key factors to ensure the proper functioning and effective design of a constructed wetland are summarized in Figure 8.

3.9. Impact of Plants on Aquaculture Productivity

Plants play multiple roles within the complex substrate–root–microorganism system, which facilitates the development of biofilms responsible for the biochemical transformation of pollutants [45]. In addition, plants absorb nutrients from wastewater that are necessary for their growth and development [89]. Many species have been studied for their role in phytoremediation through constructed wetlands, as presented in this research. However, there remains a wide variety of plant species, particularly in tropical regions with a high aquatic plant diversity, whose potential for pollutant removal is still unknown. The impact of integrating constructed wetlands (CWs) into aquaculture systems lies in the reduced use of water, which also leads to lower energy consumption for pumping and, consequently, a reduction in production costs. This aspect was evaluated by [33,53], who compared CW technology with other ecotechnologies and found CWs to be the most energy-efficient system.

Constructed wetland (CW) systems offer significant environmental and economic advantages. The evaluation results indicate that their construction is economically feasible for aquaculture production, particularly in regions with limited water availability. These systems provide effective water treatment at very low operational costs. The net present value (NPV) was estimated at USD 20,398.51, with an internal rate of return (IRR) of 17%. However, the costs of implementing such systems vary, largely depending on the economic resources available and the size of the farm. It is evident that as aquaculture systems shift toward more technically advanced closed-loop operations, costs increase. This helps explain why CWs are not yet widely adopted in Mexico.

In the case presented in Figure 9, the construction cost was USD 121.79 per square meter for a 900 m² wetland system [33,53]. In general, the cost of plants is very low because many of the most studied species grow naturally across various regions of Mexico and the world. These plants can be collected with minimal investment, considering only the labor, transportation, and planting—typically taking three days to transfer and establish them in the selected wetland site [180].

3.10. Challenges of Constructed Wetlands in Aquaculture

The primary limitation to a full-scale implementation is the lack of the dissemination of successful, practical experiences. Additionally, not all possible design options have been explored or adapted for different climatic regions where aquaculture is practiced. Although CWs have the potential for large-scale application, the aquaculture industry still faces several challenges, as illustrated in Figure 10. Therefore, future research should focus on the following key aspects:

4. Conclusions

This research has revealed that the predominant vegetation used in constructed wetlands (CWs) includes Phragmites australis, Typha latifolia, Canna indica, Eichhornia crassipes, and Arundo donax, out of a total of 43 plant species. These plants have been applied to treat wastewater generated by the production systems of 25 aquaculture species, with Oreochromis niloticus, Litopenaeus vannamei, Ictalurus punctatus, Clarias gariepinus, Tachysurus fulvidraco, and Cyprinus carpio being the most frequently reported. The use of plants in CWs for wastewater remediation is an economical and efficient strategy; however, its application is still largely limited to experimental scales. Furthermore, there remain many plant and aquaculture species yet to be studied in this context.

The evidence indicates that CW technology has been integrated into recirculating aquaculture systems (RAS) using various designs and combinations of plant and fish species. However, most studies have focused primarily on water quality variables (environmental aspect) without considering CW–RAS integration as a productive model aligned with the principles of the circular economy.

Only a limited number of studies have reported the use of plant species that are both edible for aquaculture species and safe for human consumption. Among these are Lemna minor, Ipomoea aquatica, Pistia stratiotes, and Lactuca sativa. The use of CWs in aquaculture has shown few real-scale applications, and there is a minimal number of studies focused on water reuse for agricultural purposes.

5. Future Perspectives

This opens future research opportunities aimed at promoting responsible production and consumption practices, integrating principles of the circular economy within aquaculture farms. This study highlights a significant knowledge gap in the application of constructed wetlands within the aquaculture sector. The current limited information on both plant and aquaculture species analyzed confirms the need for further research, particularly exploring underutilized plant species to assess their adaptation to CW systems. Additionally, further investigation is required for key aquaculture species and commercially valuable plants to enable CW systems not only to recycle water but also to contribute to agricultural production, thus making the technology more appealing.

It is also necessary to determine which types of full-scale wetlands are most appropriate for mitigating pollution from aquaculture effluents before they reach receiving water bodies. Moreover, research should be expanded on the types of wetlands used in aquaculture, the contaminant removal efficiencies reported, and their integration within recirculating aquaculture systems (RAS). This will help provide useful solutions for various aquaculture practices across different regions of the country. The research field remains vast and largely unexplored.

Finally, it is essential to focus on reducing hydraulic retention times (HRTs) for water purification. Therefore, future studies should investigate the addition of carbon sources, beneficial microorganisms, and artificial aeration systems that could support reducing treatment times and enhance the efficiency of integrated RAS–CW systems.