Journal of Applied Ichthyology最新文献

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.

MicroRNAs (miRNAs) are essential regulators of gene expression, influencing a wide range of biological processes, including reproduction and gonadal development. This study investigated the expression patterns of various miRNAs in the gonads of Channa striata across different reproductive stages: prespawning, spawning, and postspawning. The Gonadosomatic Index (GSI) and Hepatosomatic Index (HSI) showed significant seasonal variations, with GSI peaking during the spawning season and HSI reaching its highest value in the prespawning period, reflecting reproductive preparation. Our findings highlight the distinct roles of several miRNAs in regulating reproductive processes. The miR-21 was upregulated during spawning in both sexes, indicating its key role in gametogenesis, with persistent expression in males through postspawning, suggesting a role in sperm quality maintenance. MiR-22 also showed upregulation during spawning, supporting its involvement in gamete maturation and steroidogenesis, with reduced expression postspawning. MiR-34a was notably upregulated in male gonads postspawning, highlighting its role in spermatogenic recovery and sperm motility regulation. The miR-133 displayed complex patterns: In females, it was downregulated during spawning and upregulated postspawning, while in males, it was upregulated during spawning but downregulated afterward, highlighting its role in reproductive and metabolic processes. In addition, miR-200 was upregulated during spawning and postspawning in both sexes, underscoring its role in gamete maturation. Lastly, the miR-202-5p was consistent during prespawning and spawning in females but downregulated postspawning, with increased expression during spawning and postspawning in males, indicating its role in sperm maturation. These findings underscore a complex network of miRNAs that regulate gonadal development and reproductive success in C. striata.

Accurate fish growth and condition assessment is central to understanding the ecological health of freshwater ecosystems. Despite severe anthropogenic pressures, ecological and biometric studies of fish populations from heterogeneous habitats of the Chirchik River, a key tributary of the Syr Darya, remain poorly studied. Here, we demonstrate the length–weight relationships (LWRs) and condition factors of five freshwater fish species from the upper and middle parts of the Chirchik River, including two native and three invasive species. Observed positive (Gymnodiptychus dybowskii, Rhodeus ocellatus, and Micropercops cinctus) and isometric growth (Pseudorasbora parva and Cottus jaxartensis) patterns indicate good habitat and resource conditions in both reaches of the river. Relative condition factor (K_n) values were consistently near 1.0 and did not differ significantly among species, indicating a stable physiological status. In contrast, Fulton’s condition factor (K) varied significantly, reflecting marked interspecific differences in body robustness and energy allocation strategies. Taken together, our findings provide vital biometric data for poorly studied and heavily human-impacted rivers of Central Asia, and demonstrate the utility of combined growth and condition metrics as indicators of environmental suitability.

The Yujiang River, an important tributary of the Pearl River, flows primarily through Vietnam, Guangxi, and Yunnan in China. This cross-border watershed supports a remarkable aquatic biodiversity, especially characterized by its unique fish species. In this study, we reported the length–weight relationships (LWRs) of 13 native fish species within the Yujiang River Basin (22.156N–24.353N, 105.845E–109.608E) sampled from July 2024 to February 2025. A total of 1967 fish specimens representing the 13 species were collected using drift gillnets of various sizes (mesh size: 10–70 mm; height: 2.0–5.0  m; length: 100 m). Nonlinear regression analysis yielded coefficients of determination (r²) ranging from 0.950 to 0.996 and the parameter b spanning 2.57 to 3.74. According to the records from FishBase database and other studies, the LWRs for these 13 fish species from the Pearl River are provided for the first time in this study. Among them, the LWR of Beaufortia granulopinna, Paranemachilus genilepis, Opsariichthys duchuunguyeni, and Sarcocheilichthys caobangensis are first reported in FishBase database. The maximum body length of Ancherythroculter lini is updated to 26.00 cm. Moreover, S. caobangensis is first reported in the Yujiang River Basin in this study. It is expected that the results of this study will provide a basic data for the study of fish ecology, fishery resource management, and hydroacoustic monitoring in Yujiang River Basin.

Insulin-like growth Factor 1 (IGF1) plays a vital role in vertebrate growth, and its sexually biased expression may influence the development and evolution of sexual size dimorphism (SSD). To investigate the role of IGF1 in regulating the growth of the Chinese soft-shelled turtle (Pelodiscus sinensis), this study quantified IGF1 mRNA abundance across various tissues, phenotypes, and steroid hormone treatments using quantitative real-time polymerase chain reaction (qRT-PCR). Additionally, the polymorphism of the IGF1 gene was analyzed and genotyped using the tetra-primer amplification refractory mutation system PCR (ARMS-PCR). The findings revealed that the full-length cDNA sequence of the IGF1 gene (PsIGF1) in P. sinensis was 1790 bp, with the liver identified as the primary site of PsIGF1 expression. The expression of PsIGF1 was positively correlated with rapid growth and followed a pattern indicative of its involvement in sexually dimorphic growth. Treatment with 17α-methyltestosterone (MT) significantly increased hepatic IGF1 gene expression, while 17β-estradiol (E₂) showed the opposite effect, suggesting that IGF1 may be a critical factor underlying SSD in P. sinensis. Furthermore, a single-nucleotide polymorphism (SNP) identified in the 5′ untranslated region (UTR) of PsIGF1 was significantly associated with growth traits in P. sinensis (p value < 0.05). These results provide a foundation for further research into the regulatory mechanisms of IGF1 in the development and SSD of P. sinensis.

The present investigation was carried out in the Bhairab River, situated in the southwestern part of Bangladesh, with the aim of evaluating the impact of stocking densities on the growth performance and survival rate of Lates calcarifer (Bloch, 1790) in floating cages. In addition, the study aimed to determine the optimal stocking density for cage farming. Seabass fry, measuring an average length of 18.7 ± 2.19 cm and weighing 69.57 ± 4.86 g, were placed in nine cages. The cages were made of knotless polythene nylon net with a mesh size of 01 cm and had dimensions of 3.5 × 3 × 1.5 m. The fry were stocked at three different densities: 3, 6, and 9 individuals/m³. Their growth performance was observed every 2 weeks for a period of 6 months. The fry were nourished with live fish, equivalent to 10%-5% of their body weight. After a period of 180 days in a grow-out culture, the seabass fry achieved a length of 32.43 ± 0.57 cm and a weight of 504.56 ± 89.95 g when there were 3 individuals/m³. At a density of 6 individuals/m³, the seabass fry had a length of 29.94 ± 0.58 cm and a weight of 447.78 ± 52.76 g. Finally, at a density of 9 individuals/m³, the seabass fry had a length of 26.50 ± 0.69 cm and a weight of 331.49 ± 73.39 g. The growth exhibited allometric patterns and was not influenced by the stocking density. The survival rate was relatively greater at lower (97%) and moderate (95%) stocking levels; however, the production was significantly (p < 0.05) higher at the moderate stocking density. Lower and moderate stocking densities resulted in increased weight gain and specific growth rate (SGR). The findings of the current investigation suggest that a density of 6 individuals per cubic meter of L. calcarifer is suitable for cage culture in flowing water environments.