Aquaculture Journal

This study compared the effects of three supplementary diets—egg yolk, Artemia, and commercial pellets with 48% crude protein—on the growth performance and survival rate of redbreast tilapia (Coptodon rendalli) under intensive culture conditions at the Kamutjonga Inland Fisheries Institute in the Kavango East region of Namibia. The study was conducted from December 2023 to January 2024 using a complete randomized design replicated thrice. Results showed that fish fed with commercial pellets exhibited the highest specific growth rate (1.39 ± 0.80%) compared to egg yolk (0.94 ± 0.54%) and Artemia (0.33 ± 0.19%). Commercial pellets also had the best survival rate (76.19 ± 43.099), compared to egg yolk and Artemia (70.47 ± 40.69; 33 ± 19.05), respectively. However, egg yolk had the best feed conversion ratio (0.20 ± 0.05) compared to the commercial pellets (0.22 ± 0.04) and Artemia (0.26 ± 0.07). Critical water quality parameters were maintained within acceptable survival ranges for C. rendalli across all treatments. These findings highlight the importance of dietary protein content in optimizing the growth and survival of C. rendalli under intensive culture conditions and provide insights for effective feeding strategies. However, commercial pellets are expensive and inaccessible to small-scale fish farmers. As an alternative, egg yolk emerged as a viable and affordable feed option, promoting fish growth and supporting the establishment of small-scale farming practices in the region. Full article

Motile aeromonad septicemia (MAS), caused by the Aeromonas species, has been a serious problem in fish health management, particularly in Nile tilapia (Oreochromis niloticus). This study characterized an Aeromonas species isolated from farmed tilapia fingerlings in Binangonan, Rizal, Philippines, and tested for its pathogenicity in tank trials. The isolate, designated as Aeromonas veronii DFR01 (Diseased Fish Rizal), was identified based on 16S rRNA phylogenetic analysis, 16S rRNA homology, and MALDI-TOF mass spectrometry. Its biochemical profile was generated from API and Biolog Gen III systems. A median lethal dose of A. veronii DFR01 was determined to be 10⁷ CFU/mL in tank trials and was utilized as a whole-cell inactivated antigen for oral vaccine development. The immunized tilapia fingerlings produced elevated levels of immunoglobulin M (IgM) in the blood as determined by an enzyme-linked immunosorbent assay (ELISA). There was a significant increase in IgM levels 14 days post-vaccination. A quantitative polymerase chain reaction (qPCR) showed increasing levels of IgM gene expression after vaccination until 38 days of culture. Vaccinated fish showed 25–35% cumulative mortality after the challenge, while non-vaccinated-challenged fish showed 75% mortality. The findings of this research suggest that the fish oral vaccine may prove beneficial for farmed tilapia populations. The vaccine elicited improved immune responses in the fish and resulted in higher survival rates. Full article

Despite the huge potential of aquaculture in the Amazon, several producers have abandoned the activity due to a lack of assistance, technology, and innovation. Thus, the objective of this study was to identify factors that have contributed to the withdrawal of aquaculturists from the municipality of ‘Vigia de Nazaré’, state of Pará (Northern Region of Brazil). This case study took place in 2022 through a quanti-qualitative survey, applying structured questionnaires to former aquaculturists. A total of 30 fish farms were investigated, with 11 of them being abandoned. They are distributed across 10 rural communities that have developed fish farming, with ‘Vila de Itapuá’ (18.2%) being the most representative. When active, fish farming was practiced by men (100%) aged between 51 to 60 years (54.5%) with an incomplete primary education (100%), who carried out the activity for an average of 5 years (81.8%), quitting fish farming between the years 2019 and 2020 (72.7%). All former aquaculturists owned small properties, with excavated ponds in an extensive system and used family labor. The absence of technical assistance and the high cost of feed were pointed out as the main problems in the production chain. It is worth noting that the monoculture of Tambaqui (Colossoma macropomum) accounted for 63.6% of the species produced in rural communities. In conclusion, former aquaculturists express the desire to return to fish farming due to its socio-economic importance. For this, government actions supporting technical assistance and advanced studies in fish nutrition by educational, research, and extension institutions are necessary. Full article

This study aimed to determine the protein requirements of the fattening phase for Nile tilapia (Oreochromis niloticus) fed fish meal-free diets. A total of 75 Nile tilapia were maintained in a water recirculation system, and five isoenergetic diets were formulated with increasing protein levels encompassing three repetitions each. The findings revealed that protein levels significantly affected (p < 0.05) certain Nile tilapia performance, yield, and composition parameters. The determined parameter values clearly indicated that Nile tilapia can be fed fish meal-free soybean meal and corn-based diets. Furthermore, the metabolic plasticity of this species concerning dietary protein concentrations was also demonstrated, with adequate performance results achieved in treatments containing from 267 to 294 g/kg digestible protein (DP), or 298 to 327 g/kg crude protein (CP), where the balance between essential and non-essential amino acids and energy resulted in adequate performance correlated to satisfactory feed conversion values and filet yields and composition. A DP concentration of 267 g/kg (298 g/kg CP) is recommended when offering corn and soybean meal-based diets during the Nile tilapia fattening phase to fish weighing between 400 and 700 g. Full article

Aquaculture development is a challenge for the economic growth of coastal territories and to promote the food security of their populations. Many efforts have been made by international, national, and local public institutions to develop this sector. Despite this political objective, the coastal zones of Europe and the Mediterranean in general are faced with problems that strongly limit this development. This is linked to several factors, including social opposition, which raises the question of the social acceptability of aquaculture development. Beyond understanding the factors that explain the social rejection of this sector or its products, the key question concerns the capacity of private and public institutions to deal with this social opposition in a practical way. Based on fieldwork and a participatory approach, this paper analyzes the constraints of aquaculture development in Monastir Bay, Tunisia, and in particular, those relying on social dimensions. Under this participatory approach, the authors propose a research–action framework allowing the building of bases for engaging stakeholders in a co-construction process of a shared vision of aquaculture development in Monastir, in accordance with the constraints and ambitions expressed by the local communities regarding territorial needs. This paper shows the value of building the transition from an individual or group vision to a collective vision through a participatory approach that is likely to form a consensus, as opposed to an aggregation of individual visions that can lead to social unacceptance. It also argues that involving citizens in the exploration of aquaculture development scenarios adapted to the territory is an essential prerequisite to exploring the conditions that question the social acceptability and its improvement. Full article

Sulfated polysaccharides (SPs), especially those with immunostimulant effects on shrimp and fish, are bioactive compounds with potential use in aquaculture. In this study, Pacific white shrimp (Penaeus vannamei) were fed diets containing 0%, 0.5%, 1.0%, 1.5%, or 2.0% crude extracts from the microalga Porphyridium cruentum for 30 days. After dietary supplementation, the shrimp were exposed to Vibrio alginolyticus, allowing the assessment of phenoloxidase activity (PO) and total hemocyte count (THC) pre- and post-challenge, as well as shrimp survival rates. Shrimp that received the 1.0% treatment had greater survival (90%) at 48 h post-challenge, while the 0% and 2.0% treatments had survival rates close to 63% in the same period. Furthermore, at 48 h post-challenge, THC was significantly greater (p < 0.05) in the shrimp that received crude extract supplementation compared to that in shrimp of the control group (0%). PO showed a proportional increase according to crude extract inclusion levels. Such dose-dependency in response to PO increases became significantly greater (p < 0.05) in the 2.0% treatment group compared to that in the 0% treatment group in the pre-challenge period and that in the 0% and 0.5% treatment groups in the post-challenge period. These results showed that crude extracts from P. cruentum could be considered immunostimulants by increasing the resistance of P. vannamei exposed to V. alginolyticus, potentially representing a major breakthrough for marine shrimp farming. Full article

This study investigated the adaptability of Dunaliella salina to different salinity levels, with an emphasis on growth, pigment concentration, and desalination potential. It was found that among the 21 salinity levels, Salinity 75 produced consistently favorable results in cell count (13.08 × 10³ ± 1.41 × 10³ cells/mL), dry biomass (2.46 ± 0.06 g/L), pigment content (chlorophyll a = 97,500,000 ± 100,000 pg/L, chlorophyll b = 123,600,000 ± 300,000 pg/L), and desalination (9.32 ± 0.47 reduction). Therefore, Salinity 75 was selected for the final trial (scale-up), which revealed unanticipatedly high cell counts (58.96 × 10³ ± 535.22 cells/mL), with the dry biomass weight being statistically different (higher) than expected (4.21 ± 0.02 g/L) (p < 0.0001), most likely due to the high cell count and energy reserve storage for high-salinity adaption in the form of bio-compounds. Pigment growth continued (chlorophyll a = 95,400,000 ± 2,200,000 pg/L, chlorophyll b = 128,100,000 ± 5,100,000 pg/L), indicating pigment production under salt stress. Notably, desalination did not occur in this stage, possibly due to the necessity for a bigger initial inoculate, prolonged exposure or bioaccumulation becoming the prevailing mechanism over desalination. Nevertheless, the trial highlights D. salina’s strong adaptation to various salinity levels. This suggests a promising future in halophyte research, particularly in understanding the mechanisms that prevent salt accumulation in cells and how to overcome this barrier. Additionally, these results suggest that microalgae could be a viable resource in saline-rich environments unsuitable for conventional agriculture, promoting industrial adaptation to adverse conditions. Full article

Tenacibaculum discolor develops biofilm in marine aquaculture production tanks and is identified as one of the causative agents of tenacibaculosis, a bacterial disease that causes significant losses in marine aquaculture production. In this study, the biofilm characteristics of T. discolor strain FMCC B487 were evaluated. Cell growth and biofilm formation and development were studied in miniaturized assays to assess the effect of different levels of environmental factors temperature and salinity, as well as the presence of monosaccharides potentially found in aquaculture hatcheries. The ability of the strain to grow and develop strong biofilms in ambient to high temperatures and at salinities above 20 g/L was shown. Mannose was the monosaccharide with the most prominent impact on the T. discolor strain FMCC B487 biofilm. The composition of planktonic cell extract, biofilm extracts, and extracellular polymeric substances (EPS) produced by T. discolor strain FMCC B487 were investigated by means of colorimetric and fluorometric assays as well as analyses by electrophoresis, gas chromatography, and high-performance size-exclusion chromatography coupled with a multiangle light scattering detector, revealing the dominance of proteins and lipids and the absence of high-molecular-weight polysaccharides. This information may serve as a basis for considering anti-biofilm strategies against the pathogen T. discolor. Full article

The Italian shellfish industry mainly comprises clams, mussels, and oysters. While clam production thrives and Italy leads Europe, mussel farming faces economic challenges. Oyster production is relatively new and holds potential. Sustainable development is crucial for meeting growing seafood demand while ensuring resource conservation and food safety. This paper, part of the VALUE-SHELL project funded by the Italian Ministry of Agriculture, Food Sovereignty and Forests (MASAF) as part of support activities for the National Strategic Plan of Aquaculture, combines desk research on industry structure and public interventions using a collaborative approach involving stakeholder interviews and focus groups with producers and local entities to assess the sector’s most compelling needs. The collaborative process highlighted key challenges across the following four sustainability pillars: environmental (global warming, predator control, and pollution mitigation are critical concerns for ecosystem balance); economic (increased production costs and limited diversification opportunities affect profitability); social (fear of generational decline due to limited training and education opportunities poses a threat to the industry’s future); and institutional (lack of a dedicated aquaculture law and fragmented governance hinder long-term planning). The project identifies policy bottlenecks hindering the sector’s potential, caused by not fully addressing producer needs. Sustainable development strategies are essential for addressing these challenges and ensuring the Italian shellfish industry’s future. Full article

Chelon labrosus represents a promising species for current aquaculture to lean towards a more sustainable model. The control of reproduction in captivity is essential to develop the industrial production of new species. This work adds to the knowledge of the reproductive aspects of males and females of this species. We aim to (1) develop a methodology for sex identification of reproductive and prereproductive specimens of the studied species based on the plasma levels of steroid hormones—estradiol (E2) and 11-ketotestosterone (11-KT); (2) determine the maturity evolution of the females throughout the spawning season by gonadal biopsy; and (3) describe sperm quality throughout the breeding season (volume, motility, density). The results show that an 11-KT/E2 ratio > 0.4 is 100% effective in distinguishing males from females, provided that individuals present a size greater than that of first sexual maturity. A double trend was observed in the development of oocytes, with an increase in the initial diameter until the middle of the spawning season, followed by a divergence of the group, with some females continuing the maturation process and others going into regression. Sperm data show stable quality at the beginning and in the middle of the spawning season and a significant loss of quality at the end of the reproductive period. The present study also shows that, between the beginning and the middle of the reproductive season, males of this species can recover sperm volume removed by stripping. Full article

The study aims to characterize the immune cell landscape in convalescent Asian seabass (Lates calcarifer) blood samples after exposure to scale-drop disease virus (SDDV). Traditional immunophenotyping approaches used in human and mouse studies are impractical for non-model organisms like the Asian seabass due to the lack of specific antibody-based reagents. To overcome this challenge, 10x Genomics single-cell RNA sequencing was employed. The analysis of blood samples revealed 24 distinct leukocyte clusters, with elevated proportions of B cells, granulocytes, and T cells in the convalescent group compared to the uninfected group. While distinguishing granulocyte and macrophage subsets was challenging, the analysis of differential gene expression in the macrophage population indicated that the upregulated genes were linked to inflammatory processes. Specific T cell clusters showed notable expressions of cd4-1, cd8a, perforin-1 and il-2rβ, suggesting the presence of CD4+ T helper (Th), CD8+ cytotoxic T (Tc) cells, immature T cells, and naive T cells. Attempts to categorize CD4+ T cells into Th subtypes lacked clear distinctions, while CD8+ T cells exhibited three clusters, predominantly Tc1 cells. Furthermore, comparisons between convalescent and uninfected groups revealed increased percentages of activated and antibody-secreting B cells in the convalescent group. This single-cell analysis provides vital insights into the immune cell dynamics in convalescent and uninfected Asian seabass, providing valuable information on potential immune responses to SDDV infection. Full article

The digitisation of the agriculture industry provides an opportune context for accelerating sustainable food production. Aquaculture is among the fastest-growing agriculture sectors and is well placed to help address food supply shortages, directly contributing to the achievement of UN Sustainable Development Goal 2. However, the sector currently has inadequate digital capability and enabling conditions to thrive. Social cognitive career theory asserts that career choices and persistence are directly influenced by a person’s thoughts, including their self-efficacy; therefore, the upskilling and reskilling of labour is required to build confidence in their digital capabilities and reduce turnover intentions. Consequently, this study sought to identify the key skills and needs for this workforce to transition to digitally driven ways of working. The results indicated that a range of skills and abilities that enable people to improve their digital capabilities were required. The findings are presented and discussed. Full article

Shrimp farming in the Biofloc Technology System (BFT) is already considered an alternative to the traditional culture. The bioflocs maintain the water quality and can be used as a food supplement for shrimp. The Pacific white shrimp Litopenaeus vannamei forms the basis for most of the production in BFT. However, its culture is limited by the low temperatures. Thus, the BFT culture potential of native species, such as the pink shrimp Farfantepenaeus brasiliensis, should be considered. The present study aimed to compare the cultures of F. brasiliensis and L. vannamei in the grow-out phase in the BFT system. The experiment comprised two treatments: (FB), grown out of F. brasiliensis, and (LV), grown out of L. vannamei. The study lasted 70 days and was conducted at the Marine Station of Aquaculture at the Federal University of Rio Grande, Rio Grande do Sul State, Brazil. The stocking density was 100 shrimp/m² for both species. The shrimp were fed twice a day with commercial food. The physicochemical parameters of the water were monitored throughout the experimental period. The results showed that all physicochemical parameters of the water remained within the tolerated limits for both species. However, during the growth phase in the BFT, it was observed that the L. vannamei shrimp showed a better zootechnical performance than F. brasiliensis. The results indicate that L. vannamei has a higher capacity to catch bioflocs as supplementary food, demonstrating a better response of that species to the BFT system in the grow-out phase compared to F. brasiliensis. Full article

We determined the effects of sodium propionate (SP) added to the diets of Atractosteus tropicus juveniles with respect to the growth, survival, digestive enzyme activity, and expression of genes that are associated with the immune system. Five treatments (0, 0.5, 1.0, 1.5, and 2.0%) were evaluated in triplicate on 180 fish (3.65 ± 0.12 g) distributed among 15 (70 L) tanks. The juveniles were fed five times a day with 5% feed in relation to the biomass of the organism. The treatment with 0.5% SP showed a final weight value of 25.7 ± 4.5 g, absolute weight of gain (AWG) of 21.93 ± 4.39 g, and specific growth rate (SGR) of 3.1 ± 0.26. Treatments with 1.5 and 2.0% SP showed the highest survival (91.6%). The control group (0%) showed a greater activity of lipases. There was a tendency that the highest activity of alkaline proteases and chymotrypsin occurred in the 0 and 0.5% treatments. The maximum relative expression of the genes ocln, muc2, and nod2 occurred in the 1.5% treatment. The inclusion of SP in the diet of A. tropicus juveniles could benefit the activity of some digestive enzymes as well as the expression of genes related to the function of the intestinal barrier, therefore benefitting the survival of the organisms. Full article

Freshwater fish larviculture techniques still have deficiencies in cultivation and feeding. In this study, we evaluated experimentally different cultivation and feeding systems in the Brycon amazonicus (matrinxã) larviculture. Seven treatments with different live foods were used: T1 = a semi-intensive mesocosm system with green water; T2 = a clear water system containing Artemia sp. as food; T3 = a clear water system containing Dendrocephalus brasiliensis as food; T4 = a clear water system containing a combination of Artemia sp. and D. brasiliensis as food (a proportion of 1:1); T5, T6 and T7 were the same as T2, T3 and T4, respectively, but with a swimming exercise system. During the experiment, the water quality parameters were measured and maintained suitably for the cultures. The highest values of final weight (42.97 ± 2.58 mg) and specific growth rate (31.77 ± 0.60%) were observed in T5 (p < 0.05). Regarding the nutritional composition, the larvae of B. amazonicus that were fed nauplii of D. brasiliensis had a better profile of amino acids and essential fatty acids than those fed other live foods. Therefore, nauplii of D. brasiliensis can be used as an adequately nutritional food for larvae of B. amazonicus. Full article

The common snook (Centropomus undecimalis) is a protandric hermaphrodite fish that undergoes a sex change during its life cycle. In nature, common snook females develop directly from males shortly after spawning. However, the factors triggering this process remain unknown. This knowledge gap poses challenges for managing the species in captivity. To address this, we conducted a study on sex change induction in three-year-old males using estradiol and evaluated the potential effects of photoperiod manipulation on early maturation. Four treatment groups were employed: (1) fish with estradiol + natural photoperiod; (2) fish without estradiol + natural photoperiod; (3) fish without estradiol + controlled photoperiod; and (4) fish with estradiol + controlled photoperiod. The effectiveness of these treatments was assessed through histological procedures, which allowed for the examination of the fishes’ gonads. Furthermore, the concentration of alkali labile phosphorus in fish plasma was measured and correlated with the histological results. Our findings revealed that administering 2 mg/kg estradiol implants resulted in a remarkable 100% female population within the estradiol-treated groups. No significant effect on fish maturation was observed due to the manipulated photoperiod conditions. This protocol offers improved management strategies for captive broodstock. Firstly, the concentration of estradiol used in this study proved sufficient to induce sex change in this hermaphroditic species, enabling the production of viable females at an early age and smaller size and facilitating easier broodstock manipulation. Secondly, the implementation of the alkali labile phosphorus technique allows for sex identification without the need to sacrifice the fish. In conclusion, our study provides valuable insights into sex change induction and photoperiod manipulation in common snook. The findings contribute to enhanced management practices for captive broodstock. However, further research is needed to explore the underlying mechanisms triggering sex change and to optimize protocols for long-term maintenance and successful reproduction in captivity. Full article

One fifth of the world’s population and critical infrastructures are close to the coast and regions of high-risk sea level rise elevation. The last decades have been characterized by increasing extreme events, including storm surges, flooding, coastal erosion, enhanced coastal vulnerability with associated livelihood, and economic losses. Nature-based engineering solutions are being adopted as sustainable solutions for helping existing technologies live their design life and providing climate change adaptation and resilience for coastal and riverine communities. This paper involves the investigation of nature-based eco-hydraulic soft coastal engineering to cultivate seaweed for coastal protection. In this context, the present study involves an advanced risk evaluation performed by conducting an extreme bore interaction with seaweed as a soft engineering coastal protection measure. The load reduction on the inland structure during extreme flooding conditions, incorporating seaweed, is addressed. The present study indicates that the load on inland structures can be reduced by as much as 14% in extreme flooding conditions in the presence of seaweed with two rows of seaweed, indicating the usage of seaweed as a part of coastal protection over existing site protection infrastructure for improved coastal mitigation. Full article

Severe cannibalism can result in a significant loss of productivity during the nursery phase of Asian seabass, Lates calcarifer. The present study aimed to determine the effect of dietary tryptophan on growth, feed utilization, cannibalism, survival, and muscle proximate composition of Asian seabass juveniles (initial size, 2.77 ± 0.04 cm in length and 0.29 ± 0.01 g in weight) in a recirculating aquaculture system (RAS) at different stocking densities. The tryptophan levels were set at 0.41% (control diet, standard dosage for normal growth and survival of Asian seabass), 1.00% (Diet 1), and 1.50% (Diet 2), while the stocking densities were set at 0.5 ind./L and 1.5 ind./L. The results indicated that dietary supplementation with L-tryptophan (TRP) and fish stocking density had a significant effect on fish growth parameters, feed utilization, cannibalism, survival, and muscle lipid content (p < 0.05) over the 45-day trial. The maximum length, weight, WG, and SGR were 11.64 ± 0.35 cm, 22.93 ± 2.67 g, 22.64 ± 2.67 g, and 9.63 ± 0.27%, respectively, in the fish fed Diet 2, and 11.35 ± 0.22 cm, 24.38 ± 1.28 g, 24.09 ± 1.28 g, and 9.82 ± 0.11% at a 1.5 ind./L stocking density. The lower FCR (0.81 ± 0.04) and higher PER (2.98 ± 0.16) ensured better utilization of Diet 1 than the other diets. Moreover, significant interaction effects between diet and stocking density were observed in total yield, cannibalism, and survival of the Asian seabass. Significantly higher survival rates of 76.11 ± 3.90% in the Diet 1 group and 76.28 ± 2.88% in 0.5 ind./L stocking density were obtained, which is promising. The study concludes that dietary supplementation with 1.00% TRP was effective in reducing cannibalism and increasing the survival of the Asian seabass nursery reared in RAS at a lower stocking density (i.e., 0.5 ind./L), whereas 1.50% supplemental TRP at a higher stocking density (i.e., 1.5 ind./L) significantly increased the cannibalism and growth, which in turn reduced the survival rate. Full article

Symsagittifera roscoffensis is an intertidal Acoel flatworm that forms a symbiotic relationship with the alga Tetraselmis convolutae. Members of the genus Tetraselmis are known to have a high nutritional value and have been widely used to enrich intermediate prey for fish within the aquaculture industry; therefore, S. roscoffensis could be a good candidate as a trophic shortcut to deliver algal nutrition to fish. In this study, we investigated the likelihood of five ornamental tropical freshwater and six ornamental marine fishes to consume this worm, either as live feed or in freeze-dried form. We also tested the ability of S. roscoffensis to form a symbiotic relationship with alternative algal species, analysing the nutritional profile of S. roscoffensis when grown in different media. All the experimental fish consumed live worms to some degree, with the exception of one species (Meiacanthus grammistes); the response time to the worms ranged from 1.1–68.6 s for freshwater ornamental species to 1–24 s for marine ornamental species, and in most cases, this was comparable to or shorter than their response time to the reference diet Artemia. The fishes showed no negative effects after consuming the worms. We obtained similar results with freeze-dried worms in terms of the number of worms eaten, response time, and feeding time. Symsagittifera roscoffensis was able to form a symbiotic relationship with all the tested algal species of the genus Tetraselmis, but not with members of other genera. Worms grown in nutrient media (f/2 and f/4) had significantly higher contents of protein, pigments, and total and polyunsaturated fatty acids, including eicosapentaenoic acid (20:5n − 3) and α-linolenic acid (18:3n − 3), than those grown in seawater. These results show that S. roscoffensis was acceptable to many ornamental fish species, delivering key algal ingredients that are beneficial to fish health; hence, it is a promising alternative to conventional fish feeds for the ornamental pet trade. Full article