Journal of Applied Ichthyology最新文献

Aquaculture is an emerging sector in meeting global food demands, with significant potential to accelerate fish production. However, a major bottleneck in this industry remains the challenge of fulfilling the complex nutritional needs of fish larvae, often limited by the high cost and scarce availability of appropriate feed sources. In this study, we explored the potential of live microalga Desmodesmus sp. and nutritionally enriched copepods, administered at different concentrations, as alternative dietary supplements to enhance the growth performance and survival rate of the mrigal, Cirrhinus cirrhosus larvae. The fish larvae were reared for a period of 30 days under six feeding regimes (treatments): T₁ (10–13 × 10⁴ cells mL⁻¹ live Desmodesmus sp.), T₂ (7.5–9.5 × 10⁴ cells mL⁻¹ live Desmodesmus sp. + 5–10 individuals mL⁻¹ enriched live copepods), T₃ (5–6.5 × 10⁴ cells mL⁻¹ live Desmodesmus sp. + 10–20 individuals mL⁻¹ enriched live copepods), T₄ (2.5–3.25 × 10⁴ cells mL⁻¹ live Desmodesmus sp. + 15–30 individuals mL⁻¹ enriched live copepods), T₅ (20–40 individuals mL⁻¹ enriched live copepods), and T₆ commercial feed (0.5–1 gL⁻¹) as a control diet under laboratory environments. The T₃ diet exhibited the highest protein (17.87%) and fat (2.89%) content in the fish larvae, significantly higher than the control diet T₆ (16.63% protein, 2.28% fat). The T₃ diet significantly improved the larval growth in terms of gain in length (17.34 mm), gain in weight (118.81 mg), percent gain in length (299.69%), percent gain in weight (10,069.49%), and specific growth rate (15.83%). The highest survival rate was observed in T₃ (92.55%), followed by T₄ (90.15%), T₅ (85.48%), T₆ (84.21%), T₂ (82.44%), and T₁ (69.43%). This study highlights the potential of the combined Desmodesmus sp. and enriched copepods as diets for the rearing of mrigal larvae with an aim of sustainable aquaculture development.

Length–weight relationship (LWRs), length–length relationships (LLRs), and relative condition factor (Kn) are fundamental biological indices for fisheries stock assessment, sustainable management, and monitoring ecosystem health. This study determined the LWRs, LLRs, and Kn of three ecologically important fish species: the straightfin barb Enteromius paludinosus, the stone-lapping minnow Garra quadrimaculata, and the black lampeye Aplocheilichthys antinorii from Lake Hawassa, Ethiopia. A total of 1,420 samples (449 E. paludinosus, 176 G. quadrimaculata, and 795 A. antinorii) were collected using beach seine and hand nets in two rainy (May and June) and two dry (October and November) months of 2023. The data were analyzed using MS Excel Office 10 and IBM SPSS 27 software. The results showed that the LWRs of all considered species have a strong relationship (r²  = 0.96, 0.95, and 0.85) for E. paludinosus, G. quadrimaculata, and A. antinorii, respectively, and exhibit strong nonlinear relationships. The growth exponent (b) of G. quadrimaculata showed positive allometric growth (b > 3) and was significantly different from three (p < 0.05). However, E. paludinosus and A. antinorii showed negative allometric growth (b < 3) and were significantly different from the cube value (p < 0.05). Regarding their LLR, the coefficient of determination showed a very strong correlation (r² > 0.95) and linear relationship. No significant differences in Kn were found between sexes for E. paludinosus, G. quadrimaculata, and A. antinorii (p > 0.05). The mean relative condition factor (Kn) of all species displayed  > 1, indicating favorable Kn relative to the population average during the study period. This study provides essential baseline biological parameters for E. paludinosus, G. quadrimaculata, and A. antinorii in Lake Hawassa.

The Chinese sturgeon (Acipenser sinensis), a critically endangered anadromous species endemic to the Yangtze River, has undergone severe population decline due to habitat degradation and anthropogenic disturbances. To improve monitoring under low-abundance conditions, this study applied environmental DNA (eDNA) analysis using species-specific primers and SYBR Green quantitative PCR to investigate the spatiotemporal distribution of A. sinensis in the Yangtze River Estuary and adjacent coastal waters in May and August 2024. eDNA was detected at all sampling sites, with higher copy numbers generally observed in May, particularly in nearshore waters between Chongming and Changxing Islands. Generalized linear modeling indicated that eDNA concentrations were most closely associated with moderate temperatures, high dissolved oxygen, and slightly alkaline pH, while signal intensity declined under warmer and oxygen-poor conditions. Elevated eDNA values in May coincided with the timing of upstream release events, although the absence of prerelease baseline data prevents direct attribution to stocked individuals. Overall, the findings provide preliminary insights into seasonal habitat associations of A. sinensis in estuarine ecosystems and demonstrate the potential of eDNA as a sensitive and noninvasive tool for long-term monitoring and conservation assessment of endangered aquatic species.

On May 8, 2024, a single specimen of Epinephelus coioides was captured alive by a commercial fisher in the waters off Mataró, along the Catalan Coast in the northwestern Mediterranean (LAT 41.534N; LONG 2.457E). In this report, we document this capture and explore potential introduction vectors, presenting evidence that suggests a possible new and independent introduction of this species.

This study evaluated the protective role of amygdalin against benzo[a]pyrene (BaP) toxicity in stellate sturgeon fry (Acipenser stellatus). Fish were pre-exposed to amygdalin (5 g/kg) and subsequently challenged with sublethal BaP concentrations (50% and 75% LC50). Exposure to BaP elevated cortisol and liver enzymes (ALT, AST, ALP; p < 0.05), indicating hepatotoxic stress, whereas pretreatment with amygdalin significantly reduced ALT and AST activities (p < 0.05). Immune parameters (C3, IgM, and lysozyme) improved with amygdalin supplementation (p < 0.05) but showed only partial recovery under BaP exposure alone. Total antioxidative capacity (TAC) increased with amygdalin yet declined when combined with BaP, reflecting oxidative overload. In conclusion, the findings suggest that amygdalin may provide protective effects against BaP-induced stress and liver damage in sturgeon fry.

Trophic niche plasticity is a critical mechanism that enables fish species to adapt to diverse food resources in heterogeneous habitats; however, its specific implications for the performance of migratory juveniles through mangroves remain unclear. Thus, we comprehensively analyzed the population density, trophic niche characteristics, and body condition assessments of two juvenile populations of Mugil cephalus (Flathead grey mullet) inhabiting mangroves on the east and west coasts of Leizhou Peninsula, China. Our findings demonstrate a notable difference in niche metrics between populations with different population densities: the population with high population density had a narrower trophic niche space, higher niche redundancy, and higher trophic plasticity than the population with low density. Juveniles with high population density exhibited low Fulton condition index, indicating poorer body conditions. These empirical results support observations commonly documented in unstable environments with limited food resources, where intraspecific competition for resources tends to be prevalent. Our work contributes to the understanding of trophic niche variations among juvenile fish populations, provides valuable insights for conservation initiatives, and highlights the importance of considering the interplay among population size, trophic niche characteristics, and individual performance when designing protected areas with the aim of maximizing the nursing value for targeted species.

Mongolian grayling is a large piscivorous grayling endemic to the endorheic basin of the Khovd and Zavkhan River systems in western Mongolia. Ongoing large-scale hydropower development in the Khovd River has raised concerns about potential impacts on the Mongolian grayling populations in the area. Very little is known about the behavior and biology of Mongolian grayling, which makes it difficult to predict the impacts of damming and to plan for conservation and management mitigation actions. In this study, we used acoustic telemetry to track migration and survival of Mongolian grayling in the Khovd River system before the onset of hydropower construction. We found that the Mongolian grayling in the Khovd River conduct extensive seasonal migrations (> 170 km) to reach overwintering and spawning habitat and that migration routes pass through the Shijigtiin Canyon which is currently being developed for hydropower. We also found that Mongolian grayling in the downstream Khar Lake predominantly reside in the lake and only use lotic habitat during the spawning season, including the dammed Chono-Kharaikh River. Based on our results, we argue that the ongoing hydropower development of the Khovd River will have severe impacts on the grayling population by disrupting the annual migration cycle, prohibiting access to spawning and overwintering habitat, and altering flow regimes on downstream spawning grounds.

Wet-weight- and dry-weight-derived length–weight relationships were estimated for 68 species of mesopelagic fishes found throughout the Gulf of Mexico, 59 of which are new for the region and 28 are new globally. The length–weight relationships obtained were of good fit, with 92% of models having R² values above 0.90. Isometric and positive allometric growth were the most common growth models observed, which agrees with similar studies on mesopelagic fishes across various other regions. Allometric growth parameters (b) were largely within the expected range for fishes, with 76% of estimated growth parameters falling within the range 2.5–3.5. Estimates of growth form were variable across weight types and taxa, with 28 species displaying a different growth form depending on the weight type used. The shifts in growth form observed in this study were likely related to water content as the examination of the relationship between length and water content found that this relationship was significant in 22 of 28 species that exhibited a shift in growth form. Variations in relative water content in relation to length were hypothesized to reflect ontogenetic changes in body composition, driven by shifts in vertical distribution and diel vertical migration behavior. Overall, the present study represents one of the largest assemblies of length–weight relationships of mesopelagic fishes to date and will aid in regional biomass estimations of mesopelagic fishes in the Gulf of Mexico.

Length–weight relationship (LWR) and its parameters can be used for the development of models for the rational exploitation of fishery resources. In this study, we estimated the parameters of the LWRs and length–length relationships (LLRs) of 12 fish species caught incidentally by the artisanal whiteleg shrimp fishery in the Biosphere Reserve Marismas Nacionales (BRMN), Nayarit, Mexico. Fishes were sampled during the 2022–2024 fishing seasons (September–March) using cast nets of different mesh sizes recording total length (TL), standard length (SL), and total weight (W) for each. All LWRs and LLRs were significant (p < 0.05) with high coefficient of determination (R² > 0.89) and b-values of LWRs ranging from 2.59 (Diapterus brevirostris) to 3.14 (Elops affinis). These findings will serve as a basis for understanding the status of fish species in BRMN, an area impacted by human activity (e.g., artisanal fishing and aquaculture).

Tidal estuaries provide important spawning, nursery and feeding habitats for a wide diversity of species and serve as transit areas for diadromous fishes. However, they are globally among the most impacted aquatic ecosystems, pressured by anthropogenic alterations and global change. Assessing local fish communities and their temporal dynamics is crucial to determine the ecological baseline of these ecosystems and to serve as an indicator of their ecological status. Here, we studied the fish community in a typical estuary of the Wadden Sea in central Europe, the strongly tidal and highly anthropised River Ems. Weekly bycatch samples from a commercial stow net fishery were analysed regarding fish community composition, individual length and biomass covering fourteen consecutive months. Thirty-nine diadromous, estuarine, marine and freshwater species were recorded, amending previously reported numbers upward. Total fish abundance peaked in November 2020 and was lowest in the first half of the year 2021, corroborating previous observations of a cyclical intra-annual community pattern in estuaries. The community structure changed significantly throughout the year, coinciding with variation in water temperature, dissolved oxygen concentrations, salinity and atmospheric pressure. During most months, European smelt (Osmerus eperlanus) and flounder (Platichthys flesus) dominated in abundance, and sand gobies (Pomatoschistus spp.), European eel (Anguilla anguilla), river lamprey (Lampetra fluviatilis), three-spined stickleback (Gasterosteus aculeatus) and European perch (Perca fluviatilis) occurred in substantial shares during single months. Some historically common species such as twaite shad (Alosa fallax), houting (Coregonus cf. oxyrinchus) and Atlantic salmon (Salmo salar) showed very low abundances. The non-native Western tubenose goby (Proterorhinus semilunaris) was first recorded in this area. Intra-annual changes in abundance and length composition of species of commercial or conservational interest, e.g., smelt and river lamprey, are discussed in detail. We show that high sampling resolution and complete annual coverage are crucial for a full picture of the fish community and conclude that the ecological status of the River Ems remains poor.