Ecology of Freshwater Fish最新文献

Blue Catfish (Ictalurus furcatus) are an invasive species with expanding populations in freshwater systems, posing significant ecological challenges to native fauna. To assess their potential impacts in diverse aquatic ecosystems, we examined and compared the diets of non-native Blue Catfish from four rivers in Georgia, USA, two of which drain into the Atlantic Ocean. A total of 936 Blue Catfish were collected from the Altamaha, Ocmulgee, Oconee, and Satilla rivers, with 90.38% of stomachs containing identifiable prey. Stomach content analysis revealed that Asian Clam (Corbicula fluminea) dominated their diet in terms of number (96.76%), weight (69.33%), and to a lesser degree, frequency (36.96%). Across rivers, smaller Blue Catfish (≤ 300 mm TL) had diets with a higher relative importance of insects and vegetation. Ontogenetic dietary trends showed increasing consumption of fishes and crustaceans as fish size increased in the Altamaha, Ocmulgee, and Oconee rivers. In contrast, the Satilla River population exhibited broader dietary diversity and distinct ontogenetic shifts. Stable isotope analysis (δ¹³C and δ¹⁵N) revealed significant differences between Blue Catfish from the Altamaha and Satilla rivers, underscoring their opportunistic feeding strategies in varying habitats. Bayesian niche overlap analysis indicated that size classes within the Altamaha and Satilla rivers had substantial intraspecific overlap, with Satilla subadults exhibiting the broadest niche (SEA_B: 3.83). Factors such as prey availability, density dependence, and environmental conditions likely influence prey selection and feeding strategies in these systems. Understanding these dynamics is crucial for managing the ecological impacts of invasive Blue Catfish in freshwater systems of North America.

Rivers throughout the United States have undergone extensive modifications, altering their original dynamic state. Knowledge of how flow and temperature regime alterations may affect foraging and growth of larval fishes is limited. We investigated the effects of discharge, growing degree days (GDD) and zooplankton densities on larval Sciaenidae and Catostomidae feeding success (probability of prey encountered in the stomach), prey consumption (number of prey consumed) and growth (length at age). We sampled ichthyoplankton and zooplankton from the Des Moines and Iowa rivers, Iowa, USA from April–June 2021 and 2022. Catostomidae feeding success on cladocerans and rotifers was negatively associated with prey density, while feeding success on copepods was positively associated with prey density; consumption of cladocerans was negatively associated with prey density, and consumption of copepods and rotifers was positively associated with prey density. Discharge was positively associated with Sciaenidae feeding success and consumption of cladocerans and Catostomidae consumption of cladocerans but negatively associated with Sciaenidae feeding success on copepods, Catostomidae feeding success on cladocerans, and Catostomidae feeding success and consumption of copepods. Water temperature was negatively associated with Sciaenidae and Catostomidae feeding success and consumption of cladocerans and positively associated with Catostomidae feeding success and consumption of copepods. Larval Sciaenidae growth was positively associated with copepod density, while Catostomidae growth was positively associated with cladoceran and rotifer densities. Catostomidae growth was negatively associated with copepod density and GDD. We did not find an effect of discharge for growth of either taxa. Our results suggest zooplankton density is an important limiting factor for larval fish growth, while environmental factors such as discharge and water temperature influence larval fish foraging in lotic systems.

Young American eels ( Anguilla rostrata ) undergo a remarkable migration from oceanic spawning grounds to continental growth habitats. Impaired river connectivity can prevent facultatively catadromous eels from completing their upstream migration. The effects of barriers on the upstream migration dynamics of this endangered species remain poorly understood. This study evaluated the timing of juvenile eel migration and the spatial distribution and size/age structure of migrating eels within the tidal and hydropower-regulated Wolastoq | Saint John River in Canada. Upstream eel migration in this river is restricted by the Mactaquac Dam and Generating Station, located 150 km upstream of the sea. Approximately 36,000 eels were caught with fyke nets at various locations between the river mouth and the Mactaquac Dam, measured for length, and a subsample (n = 401) was aged via sagittal otolith readings. While glass eels (not fully pigmented juvenile eels) were observed up to 90 km upstream, approximately 20 km beyond the point of saltwater intrusion, eels arriving at the Mactaquac Dam were exclusively fully pigmented, with 80% being continental age 1+ or 2+. The mean length of juvenile eels increased with distance upstream. These results indicate that upstream eel migration in the Wolastoq | Saint John River can take multiple years and involves phases of juvenile residency. Our study provides important insights into juvenile eel migration in large rivers and implications for effective management of passage success at barriers such as hydropower dams.

The European catfish (Silurus glanis L.) is a large, non-native, invasive freshwater species known for its high fecundity, long lifespan and significant predatory potential, possibly threatening native fish communities. While some studies exist on its spatial use, most focus on its native range and lack detailed circadian and annual activity patterns. This study uses acoustic biotelemetry to track 10 adult fish in the Tagus River's Belver reservoir, employing transmitters with 3D accelerometer and pressure sensors to record activity and depth over a year. Generalised additive models identify environmental variables influencing activity and depth patterns. The European catfish is active year-round, with peak activity in summer and minimal in autumn. It occupies shallower depths in spring and summer (median depths of 2.6 and 4.8 m, respectively) and deeper waters in autumn and winter (median depths of 9.8 and 10.8 m, respectively). Circadian vertical movement patterns exhibit high seasonal and individual variability. Significant environmental predictors of the European catfish activity include river flow, water temperature and the photoperiod, while the predictors of depth use are river flow and the photoperiod. These insights can aid in developing effective control measures, such as optimising fishing efforts spatially and temporally to enhance the efficiency of removing this invasive fish.

Understanding how low salinity gradients (0‰–5‰) influence fish life cycles is critical for clarifying principles of fish assemblage formation in estuarine ecosystems. This study is intended to provide a foundation for predicting changes in fish populations amidst ongoing surface salinity decreases in the Baltic Sea. In the Neva River Estuary, differences in fish diversity and distribution between fish assemblages in freshwater and oligohaline areas were assessed using beach seine and multi-mesh gillnet surveys. The use of multiple sampling gears greatly enhanced understanding of fish distribution across salinity gradients. Fish assemblages were analysed depending on the different areas of the estuary, seasons of sampling, salinity and confounding environmental variables such as water temperature and depth. Salinity was the major influencing factor for the surf zone fish assemblages and a season of sampling was the main factor for coastal assemblages of larger fish studied with the gillnets. Fish assemblages in the surf zone exhibited significant but gradual changes in freshwater and marine-estuarine fish occurrence and abundance along the critical oligohaline barrier ‘δ-horohalinicum’ (0.5‰–1.9‰). Although freshwater species showed high occurrence and abundance throughout the estuary, their juveniles were less abundant in the oligohaline surf zone with salinity ≥ 2‰, where small-size marine-estuarine and euryhaline species predominated. Coastal multi-mesh gillnet catches showed remarkable similarity between assemblages of larger fish in freshwater and oligohaline areas. Differences in species richness and diversity indices were not pronounced throughout the salinity gradient; the decline in freshwater species was offset by an increase in marine-estuarine and euryhaline species.