Journal of Applied Ichthyology最新文献

Artificial expansion of shipping routes in the course of international trade opens up fish migration routes for numerous species. Since 2006 migration of four different goby species took place from the Ponto–Caspian region to the Lower Rhine. Neogobius fluviatilis, Neogobius melanostomus, Proterorhinus semilunaris and Ponticola kessleri were able to establish in the local fish community of the Lower Rhine. Besides the four other goby species, Knipowitschia caucasica migrated from the Ponto–Caspian region to the Lower Rhine as well in 2019. Due to increasing abundance in the last years and lack of information regarding population dynamics, feeding activity and prey preferences of the dwarf goby, the length of 1218 Caucasian dwarf gobies was analysed as well as the diet of 519 individuals in the course of May 2021 to February 2022. The populations of three different locations along the Lower Rhine were examined in winter on differences in population dynamics and feeding ecology. Analysis of the population over time suggests that K. caucasica in the Lower Rhine is an annual species with spawning during summer. The juvenile individuals of the Caucasian dwarf goby increased in total length until winter, while the adults vanished after spawning. Both juveniles and adults mainly fed on zooplankton and insect larvae. The feeding activity of the dwarf goby was higher in summer than in winter and started to increase as early as February. No difference in winter prey was recorded between populations at different sites, as all populations fed mostly on copepods and chironomids.

Establishing length–weight relationships (LWRs) is essential for conserving fish populations, especially where gaps hinder efforts, particularly crucial for elasmobranch populations in the Gulf of Guinea. This study presents LWRs established for six species of elasmobranchs landed by artisanal maritime fishing in Mayumba, located in the south of Gabon. The data were collected in May 2022 and between September 2022 and March 2023. This work provides the first LWRs for six elasmobranch species that have not yet been referenced at the regional level. One of these species, Paragaleus pectoralis, lacks referenced data on FishBase.

Caohai Lake, hailed as a gem on the Yunnan–Guizhou Plateau, is currently being faced with serious biological invasion threats. Among the most influential invasive species, the Procambarus clarkii (Girard, 1852) is causing various adverse effects on the lake’s ecosystem. However, there has been little attention paid to this issue for a long time. In light of this, this study conducted a sample collection in August 2022 to investigate the total length–weight relationships (LWRs) and condition factors (K) of the target species with the aim of providing fundamental data for the upcoming ecological restoration in Caohai Lake. The results are as follows: (1) P. clarkii was distributed throughout the lake, with females exhibiting larger body sizes than males; (2) the LWRs were expressed as: W_♂ = 2 × 10⁻⁶TL^3.66 (R² = 0.90 and n = 227); W_♀ = 4 × 10⁻⁶TL^3.39 (R² = 0.95 and n = 259), both showing positive allometric growth pattern and indicating, the weight gain rate of males is significantly faster than that of females during the growth period; (3) the K was 0.27 ± 0.04%, indicating robustness in P. clarkii in the lake. These findings underscore that urgent scientific measures should be taken to handle the rapid invasion of P. clarkii in Caohai Lake.

The population size structure and length–weight relationships (LWRs) are fundamental tools in fishery science, providing valuable insights into the health, dynamics, and management of fish populations and contributing to the sustainable use of aquatic resources. The data used in this study were estimates from the main small pelagic fishes exploited in the Gambia. They were collected using surface and bottom gillnets between November 2020 and October 2021 during scientific fishing operations. The main small pelagic fish size composition showed a modal class of 20 cm for Ethmalosa fimbriata, 21 cm for Sardinella aurita, 22 cm for Sardinella maderensis, and 30 cm for Trachurus trecae. The parameter b value of these fish species ranged from 1.6831 to 2.9461, and the correlation coefficient ranged from 0.81 to 0.95. Statistical LWRs for all species were very significant. Information obtained is essential in reviewing and establishing basic management measures for depleted shared pelagic stocks in the Gambian fisheries and the sub-region. In the context of poor data fisheries, such results also encourage the Gambian government and intergovernmental subregional organizations to support data collection in the long term.

In the present study, the DNA barcoding of the nematode parasite infecting Ompok bimaculatus and Nemacheilus anguilla fish species was carried out in Barvi Reservoir, Maharashtra. To ascertain the taxonomic status of these nematode parasites, an 18S gene marker was used. Accurate identification of fish parasites is essential to formulate preventive strategies and to study host–environment relations. The present study did barcoding of the nematode parasites of the fishes caught from the Barvi Reservoir using the nuclear 18S rDNA (SSU) sequence. The nuclear 18S rDNA (SSU) was amplified into two overlapping amplicons and sequenced to identify the species based on the sequence similarity with the NCBI GenBank database. The present study sequences (both fragments) showed 98% similarity with the species of Eustrongylides. The average genetic distance value between the present study sample and species of Eustrongylides was 0.003. In the phylogenetic tree also, the sequence was clustered with the species of Eustrongylides with significant bootstrap values. The present study identified the nematode parasite of the fish caught from the Barvi Reservoir, as species of Eustrongylides. The species-level identification could not be possible due to the insufficient/lack of reference sequences in the database. It indicates the knowledge gap concerning the species-specific molecular markers for nematode parasites of the fish.

In recent decades, climate change has significantly altered the environmental dynamics of aquatic ecosystems, profoundly impacting the intricate balance of life within them. This review paper delves into the multifaceted impacts of climate change on the physiology of aquatic life, emphasizing temperature and salinity as pivotal ecological factors unique to aquatic environments. The intricate relationship between rising global temperatures and their repercussions on freshwater and seawater habitats forms the cornerstone of this exploration. Elevated temperatures and escalating frequency of extreme heatwave events have reshaped the paradigm for fish survival, pushing them beyond optimal temperature thresholds. Furthermore, the study delves into the interconnection of seemingly disparate abiotic factors, where heightened greenhouse gas concentrations amplify coastal winds, precipitating coastal upwelling. The consequence—nutrient-rich yet oxygen-deprived waters—fuels a cascade of challenges, inducing hypoxic conditions that significantly impact aquatic organisms. The plight of fish, as ectotherms finely tuned to environmental fluctuations, is underscored, illuminating their susceptibility to temperature variations. The direct correlation between external and internal temperatures, exacerbated by climate-induced fluctuations, accentuates the urgency of addressing climate change’s impact on aquatic habitats. This review disentangles the complex web of interconnected environmental shifts, illuminating their far-reaching repercussions on the physiology of aquatic life. It emphasizes the imperative for collective endeavors aimed at understanding and addressing the challenges imposed by our evolving climate on these indispensable ecosystems.

Length-weight relationships are useful for stock assessments and modeling alternative conservation and management strategies for both native and non-native fishes. We developed length-weight relationships for 18 native and non-native riverine fishes in the lower Red River catchment. Fishes were sampled in the summer and autumn seasons between May 2021 and March 2024 via electrofishing and gill nets. Measurements for each specimen consisted of total length (mm) and weight (g). We provide L-W relationships for 14 native fishes consisting of 5 families (Lepisosteidae, Catostomidae, Ictaluridae, Sciaenidae, and Polyodontidae) and 4 non-native species belonging to the family Cyprinidae. We collected 6,845 individuals ranging from 67 alligator gar to 1,848 smallmouth buffalo. All the L-W relationships were significant (p < 0.05), and the majority (72% of species) of relationships between length and weight had r² values > 0.70. Our findings provide insight into the L-W relationships of riverine fishes and can be useful for modeling alternatives targeted at native fishes of recreational value and the removal efforts of non-native fishes.

Invasive carp populations have purported a negative influence on native biota at high densities. These invasive fishes (i.e., bighead carp Hypophthalmichthys nobilis, silver carp Hypophthalmichthys molitrix, grass carp Ctenopharyngodon idella, and black carp Mylopharyngodon piceus) each exhibit similar life history characteristics. In the Neosho River-Grand Lake system (i.e., John Redmond Reservoir, Kansas, downstream to Grand Lake O’ the Cherokees, Oklahoma), only bighead carp and grass carp have been documented to date. The distribution and status of bighead carp throughout this system were previously unknown due to limited historical data and low abundance. While few bighead carp are encountered within this system, grass carp exhibited relatively higher abundance a were used to provide insights into bighead carp. Captures of both species were used to inform management and suppression efforts. Sampling locations (n = 18) were established for environmental DNA analyses throughout the Neosho River-Grand Lake system. We sampled 13 sites using a suite of gears for standardized targeted fish sampling. All invasive carp were measured, sexed, and otoliths removed for ageing and microchemical analysis. Grass carp were processed for ploidy testing following the U.S. Fish and Wildlife Service protocol. Environmental DNA analyses generated positive results for the eDNA presence of bighead carp and silver carp. Otolith age estimates suggest fish are long lived and supported by multiple year classes. Additionally, a sampled two-year-old grass carp demonstrates spawning and recruitment potential. Otolith microchemistry suggests largescale broad movement patterns. Ploidy testing confirmed the first documented evidence of diploid grass carp in the Neosho River-Grand Lake system and revealed reproductive viability. Our results may provide future insights into locations for containment, removal, and/or eradication.

We investigated the gastric evacuation rate (GER) and maintenance ration (MR) for the adult pointhead flounder Cleisthenes pinetorum (77–421 g) at 4°C, 9°C, and 14°C which reflect the bottom, middle, and surface temperatures of their habitat in early summer. GERs were obtained from gravimetric experiments with 34 flounders fed juvenile walleye pollock Gadus chalcogrammus as prey. A 169-day feeding experiment for 67 pointhead flounders fed krill Thysanoessa inermis was undertaken to measure MR. The effects of a 10°C temperature increase (Q₁₀) on the GER and the MR were 6.55 and 2.04, respectively, indicating that the effect of temperature was greater on GER than on MR. As a result, the differences between the GER and MR, indicating the maximum amount of food ingestible for growth, were 2.8 and 30.7 cal·g⁻¹ day⁻¹ at 4 and 14°C, respectively. The water temperature on the sea floor generally remained at <4°C from winter through summer, but exceeded 10°C in the surface layer of Funka Bay, where pointhead flounders were sampled. Therefore, their growth rate should be considerably limited if they remain in the bottom layer. The unique ecology of this species among the flatfishes of floating from sea floor and feeding at pelagic zones may represent a strategy to compensate for the physiological limitation of growth at low temperatures.

To determine sex and maturity stages accurately without any physical injury and stress, especially for sensitive and high-value fish species, employing a noninvasive ultrasound imaging technique could be a desirable approach. The ultrasound imaging method as a powerful eco-friendly tool was established to determine sex, gonad volume, gonadosomatic index (GSI), and reproductive stages in the Indian shad, hilsa (Tenualosa ilisha). About 30 hilsa (15 males and 15 females) of different maturity stages were collected from the river Ganga round the year using gill nets. The ultrasound sonography (USG) was then employed in hilsa to determine the computed GSI. The fresh gonad volume of hilsa was determined using a water displacement method to ascertain actual GSI values. There was no significant difference between the calculated, real, and actual GSIs (P > 0.05) in both males and females. The validation of the precise maturity stages of ultrasound images of the gonad by the histological architecture indicated that USG images of the hilsa gonad depicted exact stages of maturity in both sexes except for stages I and II in males. The sex of the fish was accurately ascertained using ovarian ultrasound scanning for all the specimens. The calculated USG-based ovarian volume was positively correlated (R² = 0.97) with the actual and real ovarian volumes. The noninvasive and reliable ultrasonography technique was found to be an accurate and valid tool to track gender and gonadal development and predict the spawning periodicity in hilsa.