Fishes

12 pages, 1701 KiB

Open AccessArticle

Smaller Body Size and Warmer Water Improve Two Temperate Fishes’ Upstream Passage over Wetted Ramps

by Uli Reinhardt and Grace Scott Halcrow

Fishes 2025, 10(8), 401; https://doi.org/10.3390/fishes10080401 - 11 Aug 2025

Most artificial fishways allow upstream passage of large-bodied, strong-swimming fish species. Wetted ramps, which are moderate in inclination and have little water flow, could allow passage of smaller-bodied fishes over low-head dams and culverts. We observed creek chubs (Semotilus atromculatus) and [...] Read more.

Most artificial fishways allow upstream passage of large-bodied, strong-swimming fish species. Wetted ramps, which are moderate in inclination and have little water flow, could allow passage of smaller-bodied fishes over low-head dams and culverts. We observed creek chubs (Semotilus atromculatus) and white suckers (Catostomus commersonii) on wetted ramps in a laboratory setting. Smaller individuals entered the ramps at lower absolute swim velocities but exhibited superior upstream passage due to positive acceleration in the thin (<1 cm) water layer on the ramps. Larger fish displayed more pronounced, probably less efficient, head and tail amplitudes during passage. We argue that the relatively smaller depth of immersion in water was responsible for hampering the larger-bodied individuals on the ramps. Warmer water temperatures (15 °C vs. 10 °C) roughly doubled the mean distance fish traveled up the ramps. Our findings can inform fishway design for small-bodied fishes. In regions with low-head barriers against invasive sea lamprey (Petromyzon marinus), wetted ramps may help connect habitats for native fish species. Full article

(This article belongs to the Special Issue New Conservation Strategies for Freshwater and Marine Fishes: Habitat Is the Key)

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16 pages, 3173 KiB

Open AccessArticle

A Quantitative Approach to Prior Setting for Relative Biomass (B/k) in CMSY++: Application to Snow Crabs (Chionoecetes opilio) in Korean Waters

by Ji-Hyun Eom, Sung-Il Lee and Sang-Chul Yoon

Fishes 2025, 10(8), 400; https://doi.org/10.3390/fishes10080400 - 11 Aug 2025

Abstract

Snow crabs (Chionoecetes opilio), a commercially valuable species in Korean waters, have been managed under the Total Allowable Catch (TAC) system since 2002. However, stock assessment has been limited due to difficulties in estimating key ecological traits such as growth, maturity, [...] Read more.

Snow crabs (Chionoecetes opilio), a commercially valuable species in Korean waters, have been managed under the Total Allowable Catch (TAC) system since 2002. However, stock assessment has been limited due to difficulties in estimating key ecological traits such as growth, maturity, and mortality. In this study, the Bayesian Schaefer Model (BSM), implemented within CMSY++ framework, was applied to assess the stock status of snow crabs in Korean waters. BSM requires catch and abundance index data, such as catch per unit effort (CPUE) or biomass, as well as prior information on species resilience and relative biomass (B/k). To improve the reliability of B/k priors, we developed a method to calculate them quantitatively using fishery data, sales amounts, and biological information, unlike the qualitative assumptions on stock and fishing conditions proposed in previous research. Two standardized CPUE indices with differing temporal trends in recent years were used as abundance indices. To address the structural uncertainty associated with these divergent trends, we applied a grid-based approach by treating each CPUE index as an independent model scenario and integrating the posterior distributions. A total of 12,000 posterior estimates (6000 per index) were generated through the BSM and used to construct a Kobe plot. Results indicate that the current biomass is slightly above the level supporting maximum sustainable yield, and fishing mortality slightly below the optimal level, suggesting that the stock is healthy and sustainably exploited. Future research should aim to establish a systematic framework for developing quantitative B/k priors to enhance stock assessment accuracy. Full article

(This article belongs to the Special Issue Modeling Approach for Fish Stock Assessment)

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16 pages, 1769 KiB

Open AccessArticle

Analysis of Morphological Characteristics of Male and Female Gymnocypris eckloni Herzenstein

by Qiming Wang, Suxing Fu, Xiaoyi Chen, Yuting Duan, Luo Lei, Yawen Fan and Chaowei Zhou

Fishes 2025, 10(8), 399; https://doi.org/10.3390/fishes10080399 - 8 Aug 2025

Viewed by 105

Abstract

Accurate sex identification is crucial for the artificial breeding of fish species, and identification based on phenotypic traits is the preferred method owing to its low cost and rapidity. This study aimed to investigate morphological differences between male and female Gymnocypris eckloni Herzenstein. [...] Read more.

Accurate sex identification is crucial for the artificial breeding of fish species, and identification based on phenotypic traits is the preferred method owing to its low cost and rapidity. This study aimed to investigate morphological differences between male and female Gymnocypris eckloni Herzenstein. A total of 166 G. eckloni individuals (83 males and 83 females) were included, and 20 morphological indicators, including head length, snout length, and body weight, were measured. Various analytical methods, such as correlation analysis, principal component analysis, discriminant analysis, and systematic cluster analysis, were used to compare the morphological characteristics of male and female G. eckloni. The result showed significant differences in morphological characteristics between male and female individuals (p ≤ 0.05). Principal component analysis revealed five main components that collectively contributed to 83.64% of the variance, primarily including body length, fork length, total length, and body weight, highlighting the significance of these components in sex differentiation. Subsequently, a mathematical model was constructed via discriminant analysis. This model demonstrated an accuracy of 79.5% and 73.5% in identifying male and female G. eckloni, respectively, with an overall accuracy of 76.50%. Furthermore, on analyzing the relationship between body length and body weight in G. eckloni, we found differences in growth patterns between sexes. In particular, female fish usually weighed more than male fish, which was consistent with the biological characteristics and energy distribution patterns of G. eckloni. These results suggest that sexual dimorphism in G. eckloni is primarily concentrated in body shape and head morphology, which provides a reliable basis for sex identification based on morphological differences. Full article

(This article belongs to the Section Sustainable Aquaculture)

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17 pages, 1795 KiB

Open AccessArticle

Facilitation and Interference Between Native Fishes Influence Invasion Resistance

by Jeffrey E. Hill and Theresa P. Floyd

Fishes 2025, 10(8), 398; https://doi.org/10.3390/fishes10080398 - 8 Aug 2025

Viewed by 133

Abstract

Understanding the dynamics of species invasions in aquatic ecosystems is crucial for conservation and management efforts. We investigated the influence of species interactions and habitat complexity on biotic resistance to invasion by small-bodied freshwater fishes in peninsular Florida. Specifically, we focused on the [...] Read more.

Understanding the dynamics of species invasions in aquatic ecosystems is crucial for conservation and management efforts. We investigated the influence of species interactions and habitat complexity on biotic resistance to invasion by small-bodied freshwater fishes in peninsular Florida. Specifically, we focused on the interactions between two native species, Florida bass (Micropterus salmoides) and eastern mosquitofish (Gambusia holbrooki), and a common invader, the green swordtail (Xiphophorus hellerii). Our experiments included tanks with varying levels of structural complexity to mimic different habitat types. The presence of both native species significantly reduced swordtail survival, but the effect varied depending on habitat complexity. In habitats with strong predation refuge, mosquitofish facilitated bass predation on swordtails, whereas in habitats with weak predation refuge, bass suppressed mosquitofish aggression, leading to interference. Mosquitofish predominantly occupied vegetated areas and aggressively interacted with swordtails, significantly reducing invader survival. Our findings highlight the importance of considering species interactions and habitat complexity in predicting biotic resistance to invasions. We conclude that diverse interactions among native species can either enhance or impede invasion resistance, with implications for conservation and management strategies. Further research is needed to understand the broader impacts of multiple predators and competitors on invader dynamics in aquatic ecosystems. Full article

(This article belongs to the Section Biology and Ecology)

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16 pages, 6802 KiB

Open AccessArticle

Morphomolecular Characterization of Rhadinorhynchus niloticus (Acanthocephala: Rhadinorhynchidae) from Nile Perch (Lates niloticus, Perciformes: Latidae)

by Ebtsam Sayed Hassan Abdallah, Marco Albano and Hasnaa Thabit

Fishes 2025, 10(8), 397; https://doi.org/10.3390/fishes10080397 - 8 Aug 2025

Viewed by 152

Abstract

Adults of Rhadinorhynchus niloticus, a member of the Rhadinorhynchidae family, were isolated from the intestines of wild Nile perch (Lates niloticus (Linnaeus, 1758); Perciformes: Latidae) caught from the River Nile and its tributaries in Assiut City, Egypt. The parasite was found [...] Read more.

Adults of Rhadinorhynchus niloticus, a member of the Rhadinorhynchidae family, were isolated from the intestines of wild Nile perch (Lates niloticus (Linnaeus, 1758); Perciformes: Latidae) caught from the River Nile and its tributaries in Assiut City, Egypt. The parasite was found freely in the intestinal lumen with a prevalence of 10.71%, and the burden varied from one to five parasites per fish. The mean intensity and abundance were 2.16 ± 0.47 (95% CI: 1.33 to 3.17) and 0.23 ± 0.08 (95% CI: 0.11 to 0.43), respectively. The parasite was described using light and scanning electron microscopy. Molecular species identification as well as phylogenetic relationship analysis of the isolated parasite were achieved by sequencing and comparisons of the mitochondrial cytochrome oxidase C subunit I (COI) and nuclear 18S rRNA genes. The sequences were deposited in GenBank under the accession numbers PP859185 and MZ727194. Furthermore, phylogenetic analysis demonstrated that the parasites emerged from a separate branch belonging to the Rhadinorhynchidae family, which was clearly distinguished from other genospecies. Full article

(This article belongs to the Special Issue Advances in Fish Pathology and Parasitology)

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19 pages, 30477 KiB

Open AccessArticle

Impact of Novel Diets on the Distribution of Mucosal Immune Cells in the Digestive System of High-Growth Genetically Selected Gilthead Seabream (Sparus aurata) in a Long-Term Feeding Trial

by Sirine Abdeljaouad, Paula Sarmiento, Rafael Ginés, Gabriela Duque and Pedro L. Castro

Fishes 2025, 10(8), 396; https://doi.org/10.3390/fishes10080396 - 8 Aug 2025

Viewed by 198

Abstract

An alternative fish feed (ALT) replacing 50% of the fishmeal with poultry byproduct meal and insect meal and total fish oil with microalgae, poultry, and salmon byproducts oils was tested for 300 days on 900 gilthead seabream (Sparus aurata) with an [...] Read more.

An alternative fish feed (ALT) replacing 50% of the fishmeal with poultry byproduct meal and insect meal and total fish oil with microalgae, poultry, and salmon byproducts oils was tested for 300 days on 900 gilthead seabream (Sparus aurata) with an initial body weight of 17.1 ± 1.8 g (mean ± SD) of unselected (REF) and selected (HG) genotypes. Using in situ, histochemistry, and immunohistochemistry techniques, we assessed the immune response by characterizing IgT and IgM immunoglobulins, CD3ε⁺ T lymphocytes, and eosinophilic granular cells (EGCs) along the digestive system. IgT mRNA⁺ cells were concentrated in the second part of the digestive tract, while IgM⁺ predominated in the first and occasionally showed intraepithelial localization. CD3ε⁺ and EGCs were most prominent in the midgut. The diet affected IgT and IgM mRNA⁺ cells mainly in the initial part of the digestive tract. For CD3ε⁺, the diet only affected the initial and final parts, while the ALT diet increased EGC abundance across the middle compartments. Genetic selection had minimal effect on IgT⁺ and CD3ε⁺ cells, affecting only the first compartments. The REF group showed higher IgM⁺ cell abundance in specific regions, while EGCs differed between genotypes, favoring anterior accumulation in HG and ileocecal abundance in the REF group. Full article

(This article belongs to the Section Nutrition and Feeding)

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12 pages, 1450 KiB

Open AccessArticle

First Morphological and Molecular Identification of Intestinal Helminths in Wild Turbot Scophthalmus maximus (Linnaeus, 1758) Along the Bulgarian Black Sea Coast

by Alexander Atanasoff, Cigdem Urku, Elitsa Petrova-Pavlova and Feriha Tserkova

Fishes 2025, 10(8), 395; https://doi.org/10.3390/fishes10080395 - 7 Aug 2025

Viewed by 183

Abstract

Turbot Scophthalmus maximus (Linnaeus, 1758) is one of the most valuable and economically important species for the Black Sea countries. In Bulgaria, their numbers are limited and stocks are depleted; therefore, monitoring development and health status is extremely important. Internal helminths are widespread [...] Read more.

Turbot Scophthalmus maximus (Linnaeus, 1758) is one of the most valuable and economically important species for the Black Sea countries. In Bulgaria, their numbers are limited and stocks are depleted; therefore, monitoring development and health status is extremely important. Internal helminths are widespread among turbots on the Bulgarian Black Sea coast. However, description of this infection is relatively limited, and they have not been reported in scientific papers. For this purpose, a total of 36 hauls were made at depths from 15 to 90 m, and 65 turbots were examined for intestinal parasites. The present study represents the first report of internal helminths in turbot from Bulgarian marine waters through the spawning season, characterized morphologically based on a microscope observation and molecular identification. Evaluation of laboratory analyses revealed that two different parasites were determined: Bothriocephalus sp. (Müller, 1776) and Hysterothylacium aduncum (Rudolphi, 1802) and that 73.85% of the turbot were infected with one or more parasites. Based on the results, control measures and treatment for the wild population are unrealistic but should be considered for the containment and spread of diseases in aquaculture facilities. Full article

(This article belongs to the Special Issue Advances in Fish Pathology and Parasitology)

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15 pages, 662 KiB

Open AccessArticle

Genetic Structuring and Connectivity of European Squid Populations in the Mediterranean Sea Based on Mitochondrial COI Data

by Vasiliki Pertesi, Joanne Sarantopoulou, Athanasios Exadactylos, Dimitrios Vafidis and Georgios A. Gkafas

Fishes 2025, 10(8), 394; https://doi.org/10.3390/fishes10080394 - 7 Aug 2025

Viewed by 488

Abstract

Understanding population connectivity and genetic structure is crucial for the effective management of exploited marine species. This study investigates the population genetics of the common European squid (Loligo vulgaris) across the Mediterranean Sea, focusing on samples from the Aegean Sea and [...] Read more.

Understanding population connectivity and genetic structure is crucial for the effective management of exploited marine species. This study investigates the population genetics of the common European squid (Loligo vulgaris) across the Mediterranean Sea, focusing on samples from the Aegean Sea and comparative sequences from Western Mediterranean, Eastern Mediterranean, and Atlantic coasts. A total of 67 COI mitochondrial sequences were analyzed, identifying 12 haplotypes and 27 polymorphic sites. Population-level genetic diversity, pairwise F_ST values, and haplotype network analyses revealed pronounced genetic differentiation in the eastern Mediterranean contrasting with the genetic homogeneity observed among Western populations. The low haplotype diversity observed in the Greek populations of L. vulgaris may be influenced by a combination of ecological and historical factors, as the Aegean region is recognized as a hotspot of endemism and historical population fragmentation. The results indicate the existence of at least two genetically differentiated clusters within the Mediterranean basin. This study advances current knowledge of the genetic structure of Loligo vulgaris by providing novel genetic data on populations from the eastern Mediterranean, offering valuable insights for future conservation and management strategies for the species. Full article

(This article belongs to the Section Genetics and Biotechnology)

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20 pages, 3615 KiB

Open AccessArticle

Identification of Suitable Habitats for Threatened Elasmobranch Species in the OSPAR Maritime Area

by Moritz Mercker, Miriam Müller, Thorsten Werner and Janos Hennicke

Fishes 2025, 10(8), 393; https://doi.org/10.3390/fishes10080393 - 7 Aug 2025

Viewed by 177

Abstract

Protecting threatened elasmobranch species despite limited data on their distribution and abundance is a critical challenge, particularly in the context of increasing human impacts on marine ecosystems. In the northeastern Atlantic, species such as the leafscale gulper shark, Portuguese dogfish, spurdog, and spotted [...] Read more.

Protecting threatened elasmobranch species despite limited data on their distribution and abundance is a critical challenge, particularly in the context of increasing human impacts on marine ecosystems. In the northeastern Atlantic, species such as the leafscale gulper shark, Portuguese dogfish, spurdog, and spotted ray are facing pressures from overfishing, bycatch, habitat degradation, and climate change. The OSPAR Commission has listed these species as threatened and/or declining and aims to protect them by reliably identifying suitable habitats and integrating these areas into Marine Protected Areas (MPAs). In this study, we present a spatial modelling framework using regression-based approaches to identify suitable habitats for these four species. Results show that suitable habitats of the spotted ray (25.8%) and spurdog (18.8%) are relatively well represented within existing MPAs, while those of the deep-water sharks are underrepresented (6.0% for leafscale gulper shark, and 6.8% for Portuguese dogfish). Our findings highlight the need for additional MPAs in deep-sea continental slope areas, particularly west and northwest of Scotland and Ireland. Such expansions would support OSPAR’s goal to protect 30% of its maritime area by 2030 and could benefit broader deep-sea biodiversity, including other vulnerable demersal species and benthic communities. Full article

(This article belongs to the Special Issue Habitat Assessment and Conservation of Fishes)

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21 pages, 2588 KiB

Open AccessArticle

Trace Metal Contamination in Commercial Fish from the Ecuadorian Amazon: Preliminary Health Risk Assessment in a Local Market

by Gabriela Elena Echevarría Díaz, Fernando Rafael Sánchez Orellana, Rafael Enrique Yunda Vega, Jonathan Santiago Valdiviezo-Rivera and Blanca Patricia Ríos-Touma

Fishes 2025, 10(8), 392; https://doi.org/10.3390/fishes10080392 - 7 Aug 2025

Viewed by 237

Abstract

Trace metal pollution in tropical freshwater ecosystems poses growing public health concerns, particularly in regions where fisheries are central to food security; however, little is known about metal exposure risks in the Western Amazon. This study presents the first assessment of trace metal [...] Read more.

Trace metal pollution in tropical freshwater ecosystems poses growing public health concerns, particularly in regions where fisheries are central to food security; however, little is known about metal exposure risks in the Western Amazon. This study presents the first assessment of trace metal concentrations in fish sold at the main market in El Coca, a rapidly growing city in the Ecuadorian Amazon. We analyzed 11 trace metals in 17 commercially important species and estimated seven health risk indices based on two fish consumption scenarios and international reference dose standards. Our results show that all species exceeded recommended thresholds for arsenic, mercury, and lead, while one species surpassed guidelines for aluminum. Metal concentrations varied by species and river of origin: small catfish from the Payamino River had elevated cadmium, chromium, copper, and manganese levels, potentially linked to upstream gold mining, whereas larger catfish showed higher mercury and arsenic accumulation. Monte Carlo simulations of risk indices suggested overall some disease risk, but the lack of local demographic data limits accurate assessments for vulnerable groups. Despite sampling limitations, our findings offer the first baseline for monitoring trace metal exposure in the northern Ecuadorian Amazon and underscore the need for targeted public health strategies in this understudied region. Full article

(This article belongs to the Special Issue Toxicology of Anthropogenic Pollutants on Fish)

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25 pages, 5195 KiB

Open AccessArticle

Individual Fish Broadband Echo Recognition Method and Performance Analysis Oriented to Aquaculture Scenarios

by Hang Yang, Jing Cheng, Guodong Li, Shujie Wan and Jun Chen

Fishes 2025, 10(8), 391; https://doi.org/10.3390/fishes10080391 - 7 Aug 2025

Viewed by 160

Abstract

Obtaining the echo of individual fish is an important prerequisite for fisheries acoustic applications, such as in situ measurement of fish target strength and assessment of fish abundance using the counting method. It is also the foundation for evaluating the growth status of [...] Read more.

Obtaining the echo of individual fish is an important prerequisite for fisheries acoustic applications, such as in situ measurement of fish target strength and assessment of fish abundance using the counting method. It is also the foundation for evaluating the growth status of farmed fish and managing aquaculture risks. The density of farmed fish populations is typically higher, and such high-density aquaculture further increases the difficulty of obtaining individual fish echoes in practical applications. Building upon previous research and considering the behavioral characteristics of fish in aquaculture settings, this study conducted performance simulations, live fish experiments in simulated aquaculture cages, and comparative evaluations of three individual fish broadband echo detection methods based on a broadband signal system: the amplitude pulse width method (APM) based on echo envelopes, the peak detection and time delay estimation method (PDM), and the peak time delay combined with instantaneous frequency method (PDIM). This study assumed a dorsolateral fish orientation, which limits its research scope and applicability. The results showed that the PDIM achieved a detection accuracy of 78.34% and a false recognition rate of 1.32%. The APM based on echo envelopes was insensitive to individual fish echoes and had lower recognition accuracy. The PDM exhibited better individual fish echo capture capabilities, while the PDIM demonstrated superior overlapping echo rejection capabilities. Full article

(This article belongs to the Special Issue Applications of Acoustics in Marine Fisheries)

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17 pages, 2943 KiB

Open AccessArticle

Overview of a Keystone Small Pelagic Fish in the North-Western Black Sea: Biometry, Age and Stock Status of Horse Mackerel Trachurus mediterraneus (Steindachner, 1868)

by Cătălin Păun, Aurelia Țoțoiu, George Țiganov, Mădălina Galațchi, Magda Nenciu and Victor Niță

Fishes 2025, 10(8), 390; https://doi.org/10.3390/fishes10080390 - 7 Aug 2025

Viewed by 175

Abstract

As a semi-pelagic fish with commercial value, Mediterranean horse mackerel, Trachurus mediterraneus (Steindachner, 1868), is highly important both for the ecosystem, as a link between trophic levels, and for fisheries and local livelihoods. This study investigates the T. mediterraneus stock along the Romanian [...] Read more.

As a semi-pelagic fish with commercial value, Mediterranean horse mackerel, Trachurus mediterraneus (Steindachner, 1868), is highly important both for the ecosystem, as a link between trophic levels, and for fisheries and local livelihoods. This study investigates the T. mediterraneus stock along the Romanian coast for more than 10 years (2014–2024), reporting the following data on its bio-ecological characteristics and stock status: size, age, sex ratio, and estimated biomass. Horse mackerel at the Romanian coast revealed an initially slower growth rate followed by acceleration in later years, which may reflect local ecological influences such as resource availability, environmental conditions, or selective pressure. The spatial distribution of the species along the Romanian shelf indicates a clear pattern of coastal aggregation, highlighting the need for targeted and precautionary fisheries management measures, aiming to ensure a sustainable stock. Full article

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34 pages, 711 KiB

Open AccessArticle

Criteria for Consistent Broadband Pulse Compression and Narrowband Echo Integration Operation in Fisheries Echosounder Backscattering Measurements

by Per Lunde and Audun Oppedal Pedersen

Fishes 2025, 10(8), 389; https://doi.org/10.3390/fishes10080389 - 6 Aug 2025

Viewed by 129

Abstract

Generic and consistent formulations for measurement of the backscattering cross section

(σ_{b s})

and the volume backscattering coefficient

(s_{v})

using broadband pulse compression and narrowband echo integration are derived, for small- and finite-amplitude sound propagation. The theory [...] Read more.

Generic and consistent formulations for measurement of the backscattering cross section

(σ_{b s})

and the volume backscattering coefficient

(s_{v})

using broadband pulse compression and narrowband echo integration are derived, for small- and finite-amplitude sound propagation. The theory applies to backscattering operation of echosounders and sonars in general, with focus on fisheries acoustics. Formally consistent mathematical relationships for broadband and narrowband operation of such instruments are established that ensure consistency with the underlying power budget equations on average-power form, bridging a gap in prior literature. The formulations give full flexibility in choice of transmit signals and reference signals for pulse compression. Generic and general criteria for quantitative consistency between broadband and narrowband operation are derived, establishing new knowledge and analysis tools. These criteria become identical for small- and finite-amplitude sound propagation. In addition to general criteria, two special cases are considered, relevant for actual operation scenarios. The criteria serve to test and evaluate the extent to which the methods used in broadband pulse compression and narrowband echo integration operating modes are correct and consistent, and to identify and reduce experienced discrepancies between such methods. These are topics of major concern for quantitative acoustic stock assessment, underlying national and international fisheries quota regulations. Full article

(This article belongs to the Special Issue Applications of Acoustics in Marine Fisheries)

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28 pages, 1211 KiB

Open AccessReview

Phosphorus in Salmonid Aquaculture: Sources, Requirements, and System-Level Implications

by Vegard Øvstetun Flo, Torbjørn Åsgård and Odd-Ivar Lekang

Fishes 2025, 10(8), 388; https://doi.org/10.3390/fishes10080388 - 6 Aug 2025

Viewed by 247

Abstract

This review provides a comprehensive synthesis of phosphorus (P) dynamics relevant to salmonid aquaculture, with a particular focus on Atlantic salmon. It explores the global P cycle, the chemical forms of P in aquatic systems, and the implications of P sourcing, processing, and [...] Read more.

This review provides a comprehensive synthesis of phosphorus (P) dynamics relevant to salmonid aquaculture, with a particular focus on Atlantic salmon. It explores the global P cycle, the chemical forms of P in aquatic systems, and the implications of P sourcing, processing, and availability in aquafeeds. The review distinguishes between digestibility and availability of P, summarizes requirement studies, and evaluates the contribution of marine, animal, vegetable, and inorganic sources to dietary P. It also examines how aquaculture system design, particularly recirculating aquaculture systems (RASs), influences P accumulation and emissions. By integrating nutritional, physiological, and environmental perspectives, this review offers a uniquely holistic view of P efficiency and sustainability in salmonid aquaculture. Full article

(This article belongs to the Section Sustainable Aquaculture)

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18 pages, 732 KiB

Open AccessArticle

L-Arginine Effect as an Additive on Overall Performance, Health Status, and Expression of Stress Molecular Markers in Nile Tilapia (Oreochromis niloticus) Under Chronic Salinity Exposure

by Andrea Itzel Munguía-Casillas, María Teresa Viana, Miroslava Vivanco-Aranda, Luis Eduardo Ruiz-González, Emyr Saul Peña-Marín and Oscar Basilio Del Rio-Zaragoza

Fishes 2025, 10(8), 387; https://doi.org/10.3390/fishes10080387 - 6 Aug 2025

Viewed by 180

Abstract

Growing freshwater fish in saline environments is being explored as a potential solution to the freshwater shortage. However, growing these organisms in suboptimal salinity conditions leads to chronic stress that can be challenging to manage. To address this goal, it is crucial to [...] Read more.

Growing freshwater fish in saline environments is being explored as a potential solution to the freshwater shortage. However, growing these organisms in suboptimal salinity conditions leads to chronic stress that can be challenging to manage. To address this goal, it is crucial to improve the health of fish through the use of dietary supplements. This study evaluated the effects of varying levels of arginine supplementation on the growth, health status, and expression of stress-related molecular markers in juveniles of Nile tilapia exposed to chronic salinity stress. The tilapia were fed four experimental diets supplemented with 0, 1, 2, and 3% of L-arginine (T0, T1, T2, and T3). After an acclimatization period, the tilapias were exposed to a salinity level of 20‰ for 57 days in a recirculating aquaculture system. Our findings revealed that overall performance parameters were significantly influenced by L-arginine supplementation, except for the condition factor, viscerosomatic index, and hepatosomatic index. Additionally, intermediate levels of L-arginine supplementation positively influenced various blood parameters, including hematological profiles (hemoglobin and leukocytes), blood chemistry (total protein, albumin, globulin, and triglycerides), and the frequency of certain nuclear abnormalities. Furthermore, L-arginine supplementation appeared to regulate the expression of molecular markers related to stress and the immune system. In conclusion, this study indicates that L-arginine supplementation can help alleviate the chronic stress caused by salinity in juvenile Nile tilapia. Full article

(This article belongs to the Special Issue Fish Hematology)

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14 pages, 2957 KiB

Open AccessArticle

Histochemical Study of Enzyme Activity in the Digestive Tract of the Small-Spotted Catshark (Scyliorhinus canicula) and the Smooth-Hound (Mustelus mustelus)

by Lucija Devčić, Ivan Vlahek, Magdalena Palić, Valerija Benko, Siniša Faraguna, Marin Lovrić, Damir Valić and Snježana Kužir

Fishes 2025, 10(8), 386; https://doi.org/10.3390/fishes10080386 - 6 Aug 2025

Viewed by 159

Abstract

The small-spotted catshark and the smooth-hound are cartilaginous, carnivorous fish with similar depth ranges in their habitats. These two species are among the most abundant elasmobranchs in the Adriatic Sea and are frequently caught by local fishermen using longline fishing. Despite their ecological [...] Read more.

The small-spotted catshark and the smooth-hound are cartilaginous, carnivorous fish with similar depth ranges in their habitats. These two species are among the most abundant elasmobranchs in the Adriatic Sea and are frequently caught by local fishermen using longline fishing. Despite their ecological similarities, little is known about the physiological differences in their digestive processes. The study of enzymatic digestion in these ecologically relevant species helps to fill the knowledge gap in the understanding of nutrient processing in cartilaginous fish. Therefore, the aim of this study was to determine, measure and compare the enzymatic activity of alkaline phosphatase, acid phosphatase, non-specific esterase and aminopeptidase. Fish were caught in the central part of the Adriatic Sea between 2021 and 2023. A total of 60 adult individuals were analyzed, with samples taken from six parts of the digestive tract. Histochemical analysis of 1440 slides revealed clear differences in enzyme activity between the two species. In the small-spotted catshark, cellular protein degradation was most pronounced in esophagus, posterior stomach and rectum, whereas in the smooth-hound, it was concentrated in posterior stomach and spiral intestine. Cellular digestion of lipids in the small-spotted catshark appears to occur primarily in the stomach. The results of this study provide new insights into the distribution of cellular digestive enzymes in cartilaginous fish and emphasize the importance of studying the entire digestive tract as an integrated system rather than focusing on individual parts. This study fills an important knowledge gap and contributes to a deeper understanding of digestive physiology, which in turn has implications for species conservation and biological variability. Full article

(This article belongs to the Section Physiology and Biochemistry)

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17 pages, 287 KiB

Open AccessArticle

Nutritional Quality and Safety of Windowpane Oyster Placuna placenta from Samal, Bataan, Philippines

by Jessica M. Rustia, Judith P. Antonino, Ravelina R. Velasco, Edwin A. Yates and David G. Fernig

Fishes 2025, 10(8), 385; https://doi.org/10.3390/fishes10080385 - 6 Aug 2025

Viewed by 187

Abstract

The windowpane oyster (Placuna placenta) is common in coastal areas of the Philippines, thriving in brackish waters. Its shells underpin the local craft industries. While its meat is edible, only small amounts are consumed locally, most going to waste. Utilization of [...] Read more.

The windowpane oyster (Placuna placenta) is common in coastal areas of the Philippines, thriving in brackish waters. Its shells underpin the local craft industries. While its meat is edible, only small amounts are consumed locally, most going to waste. Utilization of this potential nutrient source is hindered by the lack of information concerning its organic and mineral content, the possible presence of heavy metal ions, and the risk of microbial pathogens. We report extensive analysis of the meat from Placuna placenta, harvested during three different seasons to account for potential variations. This comprises proximate analysis, mineral, antioxidant, and microbial analyses. While considerable seasonal variation was observed, the windowpane oyster was found to be a rich source of protein, fats, minerals, and carbohydrates, comparing well with the meats of other shellfish and land animals. Following pre-cooking (~90 °C, 25–30 min), the standard local method for food preparation, no viable E. coli or Salmonella sp. were detected. Mineral content was broadly similar to that reported in fish, although iron, zinc, and copper were more highly represented, nevertheless, heavy metals were below internationally acceptable levels, with the exception of one of three samples, which was slightly above the only current standard, FSANZ. Whether the arsenic was in the safer organic form, which is commonly the case for shellfish, or the more toxic inorganic form remains to be established. This and the variation of arsenic over time will need to be considered when developing food products. Overall, the meat of the windowpane oyster is a valuable food resource and its current (albeit low-level) use should lower any barriers to its acceptance, making it suitable for commercialization. The present data support its development for high-value food products in urban markets. Full article

(This article belongs to the Section Processing and Comprehensive Utilization of Fishery Products)

20 pages, 450 KiB

Open AccessArticle

Four Organic Protein Source Alternatives to Fish Meal for Pacific White Shrimp (Penaeus vannamei) Feeding

by Yosu Candela-Maldonado, Imane Megder, Eslam Tefal, David S. Peñaranda, Silvia Martínez-Llorens, Ana Tomás-Vidal, Miguel Jover-Cerdá and Ignacio Jauralde

Fishes 2025, 10(8), 384; https://doi.org/10.3390/fishes10080384 - 5 Aug 2025

Viewed by 238

Abstract

The use of eco-organic ingredients as a source of protein in aquaculture diets needs important attention due to the growing demand for organic seafood products. The present study evaluated the effects of fish meal substitution by different organic ingredients on the growth, body [...] Read more.

The use of eco-organic ingredients as a source of protein in aquaculture diets needs important attention due to the growing demand for organic seafood products. The present study evaluated the effects of fish meal substitution by different organic ingredients on the growth, body composition, retention efficiency, enzyme activity, and nutrient digestibility of white shrimp Penaeus vannamei. The four dietary formulations tested were formulated with organic ingredients and the fish meal was replaced by the following organic protein meals: Iberian pig viscera meal (PIG), trout by-product meal (TRO), insect meal (FLY), and organic vegetable meal (WHT), in addition to a control diet (CON) that included 15% fish meal. A growth trial was carried out for 83 days, raising 1 g shrimp to commercial size (20 g). Shrimp were stocked at 167 shrimp/m³ (15 individuals per 90 L tank). The results showed that the growth obtained by shrimp fed with TRO (19.27 g) and PIG (19.35 g) were similar in weight gain to the control diet (20.76 g), while FLY (16.04 g) and WHT (16.73 g) meals resulted in a significant lower final weight. The FLY diet showed significantly lower protein digestibility (68.89%) compared to the CON, PIG, TRO, and WHT diets, and significantly higher trypsin activity (0.17 mU/g) compared to shrimp fed with the PIG, TRO, and WHT diets. Shrimp fed with WHT have a significantly lower body weight percentage of protein (19.69%) than shrimp fed with the WHT and TRO diets, and some significant differences in dietary aminoacidic levels affecting amino acid body composition. These results indicate that Iberian pig viscera and trout by-product meal can successfully replace fish meal in Pacific white shrimp aquaculture. Full article

(This article belongs to the Special Issue Advances in Aquaculture Feed Additives)

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24 pages, 34309 KiB

Open AccessArticle

Assessing the Motile Fauna of Eastern Mediterranean Marine Caves

by Markos Digenis, Michail Ragkousis, Charalampos Dimitriadis, Stelios Katsanevakis and Vasilis Gerovasileiou

Fishes 2025, 10(8), 383; https://doi.org/10.3390/fishes10080383 - 5 Aug 2025

Viewed by 536

Abstract

Although marine caves are among the most species-diverse habitats in the Mediterranean Sea, most available studies have focused on their sessile fauna. This study provides the first quantitative assessment of motile fauna in 27 marine caves across four geographical subareas of the Aegean [...] Read more.

Although marine caves are among the most species-diverse habitats in the Mediterranean Sea, most available studies have focused on their sessile fauna. This study provides the first quantitative assessment of motile fauna in 27 marine caves across four geographical subareas of the Aegean and Ionian Seas, using a rapid assessment visual census protocol, applied through 3 min time transects in each ecological cave zone. Multivariate analysis revealed that the motile community structure of the cave entrance was differentiated from that of the semidark and dark zones. Deeper caves were distinct from shallower ones while caves of the east Aegean differed from those around Crete Island. A total of 163 taxa were recorded, 27 of which are reported herein for the first time in marine caves of the eastern Mediterranean Sea, while three species (two native and one introduced) are recorded in Greek waters for the first time, enriching our knowledge on the permanent and occasional cave residents. Seventeen species were introduced, comprising more than half of the total fish abundance in the southeasternmost cave. Our limited knowledge of the motile fauna of Mediterranean marine caves coupled with the continued spread of introduced species highlights the urgent need for monitoring and conservation actions, especially within marine protected areas. Full article

(This article belongs to the Section Biology and Ecology)

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15 pages, 1539 KiB

Open AccessArticle

Microplastics Induce Structural Color Deterioration in Fish Poecilia reticulata Mediated by Oxidative Stress

by Hong-Yu Ren, Huan-Chao Ma, Rui-Peng He, Cong-Cong Gao, Bin Wen, Jian-Zhong Gao and Zai-Zhong Chen

Fishes 2025, 10(8), 382; https://doi.org/10.3390/fishes10080382 - 5 Aug 2025

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Abstract

Microplastics (MPs) can affect fish health by inducing oxidative stress, but their impact on structural coloration remains poorly understood. This study investigated the effects of environmentally relevant concentrations (16 and 160 μg/L) of MPs and nanoplastics (NPs) exposure on growth, oxidative stress and [...] Read more.

Microplastics (MPs) can affect fish health by inducing oxidative stress, but their impact on structural coloration remains poorly understood. This study investigated the effects of environmentally relevant concentrations (16 and 160 μg/L) of MPs and nanoplastics (NPs) exposure on growth, oxidative stress and structural coloration in blue strain guppy fish (Poecilia reticulata). Results showed exposure to 160 μg/L MPs significantly reduced specific growth rate of fish compared to controls. Plastic accumulation followed a dose-dependent pattern, especially within gut concentrations. Oxidative stress responses differed between MPs and NPs: 160 μg/L MPs decreased SOD activity in skin and reduced GSH levels, while 160 μg/L NPs increased MDA levels in gut tissues, indicating severe lipid peroxidation. Structural coloration analysis revealed exposure to 160 μg/L MPs decreased lightness and increased yellowness, demonstrating reduced blue coloration. This was accompanied by an increase in skin uric acid content, suggesting that guanine conversion might occur to combat oxidative stress. These findings demonstrate that MPs, particularly at high concentrations, impair growth and induce oxidative stress in guppies. To counteract stress, guanine in iridophores may be converted into uric acid, leading to a decline in structural coloration. This study is the first to reveal that MPs disrupt structural coloration of fish, providing new insights into the ecological risks of plastic pollution on aquatic organisms. Full article

(This article belongs to the Special Issue Impact of Climate Change and Adverse Environments on Aquaculture)

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18 pages, 903 KiB

Open AccessArticle

Effect of Allyl-Isothiocyanate Release from Black Mustard (Brassica nigra) Seeds During Refrigerated Storage to Preserve Fresh Tench (Tinca tinca) Fillets

by María José Rodríguez Gómez, María Alejo Martínez, Raquel Manzano Durán, Daniel Martín-Vertedor and Patricia Calvo Magro

Fishes 2025, 10(8), 381; https://doi.org/10.3390/fishes10080381 - 5 Aug 2025

Viewed by 205

Abstract

The aim of this study was to prevent the development of microorganisms in the refrigerated storage of tench by releasing allyl isothiocyanate (AITC) produced by black mustard seeds. Tench reared in an aquaculture centre were sacrificed and the fillets were separated. Different amounts [...] Read more.

The aim of this study was to prevent the development of microorganisms in the refrigerated storage of tench by releasing allyl isothiocyanate (AITC) produced by black mustard seeds. Tench reared in an aquaculture centre were sacrificed and the fillets were separated. Different amounts of defatted mustard seed (300, 400 and 500 mg) were added to hermetic polypropylene trays. Microbiological, sensory, and gas chromatography with MS detection analysis were done. AITC release increased progressively until the third day of storage, significantly delaying the development of microorganisms in samples with higher mustard seed content. The tasting panel detected positive aromas at the beginning of the study, but these decreased and negative aromas appeared. The mustard seed treatment resulted in a higher positive aroma at the end of the storage, reducing rotting and ammonia odours. A total of 31 volatile compounds were detected and grouped into hydrocarbon, alcohol, benzenoid, isothiocyanate, ketone, acetate, aldehyde, and others. Butylated hydroxytoluene, an indicator of bacterial contamination, was the major aromatic compound found during storage. The release of AITC resulted in fewer organic compounds with negative aromas appearing during storage. PCA analysis allowed us to classify the assays during storage according to their volatile profiles, confirming the differences observed between treatments. Thus, adding mustard seed to fish packaging could be a viable alternative to extending the product’s shelf life and ensuring food safety. Full article

(This article belongs to the Section Processing and Comprehensive Utilization of Fishery Products)

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19 pages, 3457 KiB

Open AccessArticle

Transcriptome Analysis Revealed the Immune and Metabolic Responses of Grass Carp (Ctenopharyngodon idellus) Under Acute Salinity Stress

by Leshan Ruan, Baocan Wei, Yanlin Liu, Rongfei Mu, Huang Li and Shina Wei

Fishes 2025, 10(8), 380; https://doi.org/10.3390/fishes10080380 - 5 Aug 2025

Viewed by 254

Abstract

Freshwater salinization, an escalating global environmental stressor, poses a significant threat to freshwater biodiversity, including fish communities. This study investigates the grass carp (Ctenopharyngodon idellus), a species with the highest aquaculture output in China, to elucidate the molecular underpinnings of its [...] Read more.

Freshwater salinization, an escalating global environmental stressor, poses a significant threat to freshwater biodiversity, including fish communities. This study investigates the grass carp (Ctenopharyngodon idellus), a species with the highest aquaculture output in China, to elucidate the molecular underpinnings of its physiological adaptations to fluctuating salinity gradients. We used high-throughput mRNA sequencing and differential gene expression profiling to analyze transcriptional dynamics in intestinal and kidney tissues of grass carp exposed to heterogeneous salinity stressors. Concurrent serum biochemical analyses showed salinity stress significantly increased Na⁺, Cl⁻, and osmolarity, while decreasing lactate and glucose. Salinity stress exerted a profound impact on the global transcriptomic landscape of grass carp. A substantial number of co-regulated differentially expressed genes (DEGs) in kidney and intestinal tissues were enriched in immune and metabolic pathways. Specifically, genes associated with antigen processing and presentation (e.g., cd4-1, calr3b) and apoptosis (e.g., caspase17, pik3ca) exhibited upregulated expression, whereas genes involved in gluconeogenesis/glycolysis (e.g., hk2, pck2) were downregulated. KEGG pathway enrichment analyses revealed that metabolic and cellular structural pathways were predominantly enriched in intestinal tissues, while kidney tissues showed preferential enrichment of immune and apoptotic pathways. Rigorous validation of RNA-seq data via qPCR confirmed the robustness and cross-platform consistency of the findings. This study investigated the core transcriptional and physiological mechanisms regulating grass carp’s response to salinity stress, providing a theoretical foundation for research into grass carp’s resistance to salinity stress and the development of salt-tolerant varieties. Full article

(This article belongs to the Special Issue Adaptation and Response of Fish to Environmental Changes)

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21 pages, 4907 KiB

Open AccessArticle

Integrated Transcriptomic and Metabolomic Analysis Reveals the Molecular Mechanisms Involved in the Adaptations of Mandarin Fish (Siniperca chuatsi) to Compound Feed

by Yunyun Yan, Yuan Zhang, Junjian Dong, Fubao Wang, Hetong Zhang, Fengying Gao, Xing Ye, Chengbin Wu and Chengfei Sun

Fishes 2025, 10(8), 379; https://doi.org/10.3390/fishes10080379 - 4 Aug 2025

Viewed by 205

Abstract

Siniperca chuatsi is an important high-quality freshwater aquaculture species in China. In nature, it feeds exclusively on live food. In this study, domesticated juvenile S. chuatsi were divided into three groups and fed live food (group L), compound feed (group C), or [...] Read more.

Siniperca chuatsi is an important high-quality freshwater aquaculture species in China. In nature, it feeds exclusively on live food. In this study, domesticated juvenile S. chuatsi were divided into three groups and fed live food (group L), compound feed (group C), or a mixed diet (group M) for three months to investigate the molecular mechanisms underlying adaptation to compound feed. Histopathological examination revealed that compound feed consumption induced looser liver cell arrangement, hepatocyte morphological irregularities, and vacuolization. A total of 1033 and 1428 differentially expressed genes (DEGs), and 187 and 184 differential metabolites (DMs), were identified in the C vs. L and C vs. M groups, respectively. Transcriptomic analysis revealed that the significantly and commonly enriched metabolic pathways shared by both comparison groups were predominantly involved in amino acid, carbohydrate, and lipid metabolisms. Metabolomic analysis demonstrated that the significantly and commonly enriched metabolic pathways shared by both comparison groups were the arachidonic acid metabolism, linoleic acid metabolism, oxidative phosphorylation, and PPAR signalling pathways. Integrated omics analysis showed that the PPAR signalling pathway was the only significantly co-enriched pathway across both omics datasets. This study provides new insights into the molecular mechanisms of compound feed adaptation and provides theoretical support for selecting feed traits in S. chuatsi. Full article

(This article belongs to the Section Genetics and Biotechnology)

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20 pages, 3354 KiB

Open AccessArticle

An Assessment of the Population Structure and Stock Dynamics of Megalobrama skolkovii During the Early Phase of the Fishing Ban in the Poyang Lake Basin

by Xinwen Huang, Qun Xu, Bao Zhang, Chiping Kong, Lei Fang, Xiaoping Gao, Leyi Sun, Lekang Li and Xiaoling Gong

Fishes 2025, 10(8), 378; https://doi.org/10.3390/fishes10080378 - 4 Aug 2025

Viewed by 154

Abstract

The ten-year fishing ban on the Yangtze River aims to restore aquatic biodiversity and rebuild fishery resources. Megalobrama skolkovii, a key species in the basin, was investigated using 2024 data to provide a preliminary assessment of its population structure, stock dynamics, and [...] Read more.

The ten-year fishing ban on the Yangtze River aims to restore aquatic biodiversity and rebuild fishery resources. Megalobrama skolkovii, a key species in the basin, was investigated using 2024 data to provide a preliminary assessment of its population structure, stock dynamics, and early recovery. Age analysis (n = 243) showed that 1–6-year-olds were dominated by fish aged 3 (35%), with few older than 4, indicating moderate structural truncation. Growth parameters modeled by the von Bertalanffy Growth Function yielded L_∞ = 61.89 cm and k = 0.25 year⁻¹, with a weight–growth inflection age of 4.4 years. Natural mortality (M = 0.48 year⁻¹) was estimated using Pauly’s empirical formula, and total mortality (Z = 0.55 year⁻¹) was estimated from the catch curve analysis. While fishing mortality (F) was statistically indistinguishable from zero, a plausible low-intensity fishing scenario was explored to assess potential impacts of residual activities. Length-based indicators (LBIs) showed P_mat = 46.05%, P_opt = 9.51%, and P_mega = 6.88%, suggesting reproductive recovery but incomplete structural restoration. These preliminary findings reveal an asymmetrical recovery trajectory, whereby physiological improvements and enhanced recruitment have occurred, yet full structural restoration remains incomplete. This underscores the need for continued, long-term conservation and monitoring to support population resilience. Full article

(This article belongs to the Section Biology and Ecology)

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12 pages, 1209 KiB

Open AccessArticle

Contribution to Morphometrics and Ecology of Snow Trout (Schizothorax eurycephalus) and Stone Loach (Triplophysa ferganaensis)

by Erkin Karimov, Otabek Omonov, Pieterjan Verhelst, Bakhtiyor K. Karimov, Martin Schletterer and Daniel S. Hayes

Fishes 2025, 10(8), 377; https://doi.org/10.3390/fishes10080377 - 4 Aug 2025

Viewed by 195

Abstract

The mountainous rivers of Central Asia host diverse ichthyofauna threatened by increasing anthropogenic pressures, particularly water pollution, abstraction, and hydropower development. This study provides valuable morphometric and ecological data for Schizothorax eurycephalus (snow trout) and Triplophysa ferganaensis (stone loach) in the Shakhimardan River [...] Read more.

The mountainous rivers of Central Asia host diverse ichthyofauna threatened by increasing anthropogenic pressures, particularly water pollution, abstraction, and hydropower development. This study provides valuable morphometric and ecological data for Schizothorax eurycephalus (snow trout) and Triplophysa ferganaensis (stone loach) in the Shakhimardan River basin, Uzbekistan. S. eurycephalus exhibited positive allometric growth, while T. ferganaensis showed negative near-isometric growth. The mean Fulton’s Condition Factor was 1.0 for S. eurycephalus and 0.7 for T. ferganaensis, with site-specific variations. Strong correlations among morphometric parameters, particularly length–height relationships, support non-invasive monitoring techniques. Dietary analysis revealed S. eurycephalus was predominantly herbivorous, with around 70% algae consumption. Early sexual maturity was observed in S. eurycephalus males, whereas T. ferganaensis showed no clear maturity signs, but swollen bellies suggested ongoing or recent reproductive activity. These baseline morphometric and ecological data establish a solid foundation for future ecological assessments, conservation strategies, and the design and monitoring of mitigation measures to address anthropogenic impacts in this vulnerable region. Full article

(This article belongs to the Section Biology and Ecology)

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23 pages, 676 KiB

Open AccessFeature PaperReview

Stunted Versus Normally Growing Fish: Adapted to Different Niches

by Bror Jonsson

Fishes 2025, 10(8), 376; https://doi.org/10.3390/fishes10080376 - 4 Aug 2025

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Abstract

This literature-based review draws on studies of thirty-four fish species; most are from northern temperate regions. Fish have flexible and indeterminate growth, and often they do not reach their growth and size potential. They may become stunted with impaired growth and early maturity, [...] Read more.

This literature-based review draws on studies of thirty-four fish species; most are from northern temperate regions. Fish have flexible and indeterminate growth, and often they do not reach their growth and size potential. They may become stunted with impaired growth and early maturity, chiefly as a phenotypically plastic reaction. The main causes of stunted growth are negatively density-dependent food availability and keen intraspecific competition leading to environmental stress. Typically, their growth levels off early in life as energy consumptions approach energy costs of maintenance. Females typically attain maturity soon after the energy surplus from feeding starts to decrease. Males are often more variable in size at maturity owing to alternative mating strategies, and their size at maturity depends on both species-specific mating behaviours and environmental opportunities. In polyphenic/polymorphic populations, one phenotype may be stunted and the other phenotype non-stunted; stunted individuals do not perform the required ontogenetic niche shift needed to grow larger. The adult morphology of stunted fish is typically like the morphology of juveniles. Their secondary sexual characters are less pronounced, and they phenotypically retain adaptation to their early feeding niche, which is different from that of large-growing individuals. There are open questions regarding to what extent genetics and epigenetics regulate the life histories of stunted phenotypes. Full article

(This article belongs to the Special Issue Habitat as a Template for Life Histories of Fish)

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14 pages, 3622 KiB

Open AccessArticle

Environmental DNA Metabarcoding as a Tool for Fast Fish Assessment in Post-Cleanup Activities: Example from Two Urban Lakes in Zagreb, Croatia

by Matej Vucić, Thomas Baudry, Dušan Jelić, Ana Galov, Željko Pavlinec, Lana Jelić, Biljana Janev Hutinec, Göran Klobučar, Goran Slivšek and Frédéric Grandjean

Fishes 2025, 10(8), 375; https://doi.org/10.3390/fishes10080375 - 4 Aug 2025

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Abstract

This study evaluated the effectiveness of eDNA metabarcoding in assessing fish communities in two urban lakes (First Lake and Second Lake) in Zagreb, Croatia, following IAS removal. Water samples were collected in April and June 2024 and analyzed using MiFish primers targeting the [...] Read more.

This study evaluated the effectiveness of eDNA metabarcoding in assessing fish communities in two urban lakes (First Lake and Second Lake) in Zagreb, Croatia, following IAS removal. Water samples were collected in April and June 2024 and analyzed using MiFish primers targeting the 12S rRNA gene. The results indicated that the cleanup efforts were largely successful, as several IAS previously recorded in these lakes were not detected (Ameiurus melas, Lepomis gibbosus, and Hypophthalmichthys spp.). However, some others persisted in low relative abundances, such as grass carp (Ctenopharyngodon idella), topmouth gudgeon (Pseudorasbora parva), and prussian/crucian carp (Carassius sp.). Species composition differed between lakes, with common carp (Cyprinus carpio) dominating Maksimir First Lake, while chub (Squalius cephalus) was prevalent in Maksimir Second Lake. Unexpected eDNA signals from salmonid and exotic species suggest potential input from upstream sources, human activity, or the nearby Zoo Garden. These findings underscore the utility of eDNA metabarcoding in biodiversity monitoring and highlight the need for continuous surveillance and adaptive management strategies to ensure long-term IAS control. Full article

(This article belongs to the Special Issue Mapping and Monitoring Aquatic Biodiversity in Hotspot Habitat Areas Using Environmental DNA (eDNA))

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20 pages, 1639 KiB

Open AccessCase Report

The Power of Preventive Protection: Effects of Vaccination Strategies on Furunculosis Resistance in Large-Scale Aquaculture of Maraena Whitefish

by Kerstin Böttcher, Peter Luft, Uwe Schönfeld, Stephanie Speck, Tim Gottschalk and Alexander Rebl

Fishes 2025, 10(8), 374; https://doi.org/10.3390/fishes10080374 - 4 Aug 2025

Viewed by 327

Abstract

Furunculosis caused by Aeromonas salmonicida poses a significant challenge to the sustainable production of maraena whitefish (Coregonus maraena). This case report outlines a multi-year disease management strategy at a European whitefish facility with two production departments, each specialising in different life-cycle [...] Read more.

Furunculosis caused by Aeromonas salmonicida poses a significant challenge to the sustainable production of maraena whitefish (Coregonus maraena). This case report outlines a multi-year disease management strategy at a European whitefish facility with two production departments, each specialising in different life-cycle stages. Recurrent outbreaks of A. salmonicida necessitated the development of effective vaccination protocols. Herd-specific immersion vaccines failed to confer protection, while injectable formulations with plant-based adjuvants caused severe adverse reactions and mortality rates exceeding 30%. In contrast, the bivalent vaccine Alpha Ject 3000, containing inactivated A. salmonicida and Vibrio anguillarum with a mineral oil adjuvant, yielded high tolerability and durable protection in over one million whitefish. Post-vaccination mortality remained low (3.3%), aligning with industry benchmarks, and furunculosis-related losses were fully prevented in both departments. Transcriptomic profiling of immune-relevant tissues revealed distinct gene expression signatures depending on vaccine type and time post-vaccination. Both the herd-specific vaccine and Alpha Ject 3000 induced the expression of immunoglobulin and inflammatory markers in the spleen, contrasted by reduced immunoglobulin transcript levels in the gills and head kidney together with the downregulated expression of B-cell markers. These results demonstrate that an optimised injectable vaccination strategy can significantly improve health outcomes and disease resilience in maraena whitefish aquaculture. Full article

(This article belongs to the Special Issue Fish Pathogens and Vaccines in Aquaculture)

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18 pages, 314 KiB

Open AccessArticle

The Economic Contributions of the Virginia Seafood Industry and the Effects of Virginia Seafood Products in Retail Stores and Restaurants in 2023

by Fernando H. Gonçalves, Jonathan van Senten and Michael H. Schwarz

Fishes 2025, 10(8), 373; https://doi.org/10.3390/fishes10080373 - 2 Aug 2025

Viewed by 354

Abstract

Virginia’s coastal location and abundant marine resources make its seafood industry a vital contributor to the state’s economy, supporting both local communities and tourism. This study applied input–output models and updates the economic contributions of the Virginia seafood industry using 2023 data, building [...] Read more.

Virginia’s coastal location and abundant marine resources make its seafood industry a vital contributor to the state’s economy, supporting both local communities and tourism. This study applied input–output models and updates the economic contributions of the Virginia seafood industry using 2023 data, building on models developed for 2019 that capture both direct effects and broader economic ripple effects. In 2023, the industry generated USD 1.27 billion in total economic output and supported over 6500 jobs—including watermen, aquaculture farmers, processors, and distributors—resulting in USD 238.3 million in labor income. Contributions to state GDP totaled USD 976.7 million, and tax revenues exceeded USD 390.4 million. The study also evaluates the economic role of Virginia seafood products sold in retail stores and restaurants, based on secondary data sources. In 2023, these sectors generated USD 458 million in economic output, supported more than 3600 jobs, produced USD 136.7 million in labor income, and USD 280.8 million in value-added. Combined tax contributions surpassed USD 74 million. Importantly, the analysis results for the Virginia seafood products from retail and restaurant should not be summed to the seafood industry totals to avoid double-counting, as seafood products move as output from one sector as an input to another. These results provide evidence-based insights to guide decision-making, inform stakeholders, and support continued investment in Virginia’s seafood supply chain and related economic activities. Full article

(This article belongs to the Section Fishery Economics, Policy, and Management)

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17 pages, 4136 KiB

Open AccessArticle

The Effects of Interactions Between Key Environmental Factors on Non-Specific Indicators in Carassius auratus

by Bin Wang, Hang Yang, Hanping Mao and Qiang Shi

Fishes 2025, 10(8), 372; https://doi.org/10.3390/fishes10080372 - 2 Aug 2025

Viewed by 257

Abstract

Carassius auratus exhibits significant physiological and behavioral alterations under the combined stress of temperature and dissolved oxygen (DO) fluctuations, which are common challenges in aquaculture. In this investigation, we employed controlled thermal and DO gradients to characterize the multidimensional response profile of this [...] Read more.

Carassius auratus exhibits significant physiological and behavioral alterations under the combined stress of temperature and dissolved oxygen (DO) fluctuations, which are common challenges in aquaculture. In this investigation, we employed controlled thermal and DO gradients to characterize the multidimensional response profile of this species. The key findings revealed that thermal elevation profoundly influenced blood glucose and cortisol concentrations. Notably, exposure to hyperoxic conditions markedly attenuated stress responses relative to hypoxia at equivalent temperatures: cortisol levels were significantly suppressed (reductions of 60.11%, 118.06%, and 34.72%), while blood glucose levels exhibited concurrent increases (16.42%, 26.43%, and 26.34%). Distinctive behavioral patterns, including floating head behavior, surface swimming behavior, and rollover behavior, were identified as indicative behaviors of thermal–oxygen stress. Molecular analysis demonstrated the upregulated expression of stress-associated genes (HSP70, HSP90, HIF-1α, and Prdx3), which correlated temporally with elevated cortisol and glucose concentrations and the manifestation of stress behaviors. Furthermore, a muscle texture assessment indicated that increased DO availability mitigated the textural deterioration induced by heat stress. Collectively, this work establishes an authentic biomarker framework, providing crucial threshold parameters essential for the development of intelligent, real-time environmental monitoring and dynamic regulation systems to enhance climate-resilient aquaculture management. Full article

(This article belongs to the Special Issue Adaptation and Response of Fish to Environmental Changes)

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