Ecology of Freshwater Fish最新文献

Bartram's Bass Micropterus sp. cf. coosae is endemic to the Upper Savannah River Basin of the southeastern United States, and is threatened by hybridization with invasive Alabama Bass M. henshalli. Quantifying movement of these species and their hybrids will improve understanding of how nonnative alleles spread among riverine fish populations. We quantified summer/autumn movement of Bartram's Bass, Alabama Bass and hybrid bass in Eastatoee Creek—a tributary experiencing ongoing invasion from Keowee Reservoir. To do this, we first quantified factors associated with the longitudinal distribution and weekly movement rates of each species, then estimated probabilities of species transitioning among key habitats at the river-reservoir interface. We tagged 291 fish with passive integrated transponder tags, sampling the entire stream length of Eastatoee Creek four times in both 2021 and 2022. We radio-tagged an additional 52 fish and tracked them from early May through mid-October each year. We used mixed effect models and a Bayesian multistate model to quantify movement, river position, movement probability and the effects of abiotic factors thereon. Alabama Bass and hybrid bass moved more than Bartram's Bass and remained in the lower reaches of Eastatoee Creek, apparently restricted by a reach of high-gradient habitat that functioned as a natural barrier. Alabama Bass made greater upstream movements during cooler spring temperatures when higher reservoir levels inundated the creek mouth. Bartram's Bass were distributed throughout Eastatoee Creek, making shorter weekly upstream movements associated with increasing temperature in late spring. Movement of hybrid bass from lower portions of tributaries is likely a primary source of nonnative allele spread in this system.

Many freshwater fish populations are increasingly required to respond to warming waters and low dissolved oxygen concentrations as a result of land-use change and climate change. In addition, the average size of fish in harvested populations can be drastically reduced due to heavy fishing pressure. These factors may be more pronounced in African countries due to current high rates of forest conversion and a greater dependency on local fish catch. To investigate the relationship between fish body size and heat tolerance, we compared the upper thermal tolerance limits (estimated as the Critical Thermal Maximum, CT_max) of the smooth-head catfish (Clarias liocephalus), a facultative air-breathing fish, sampled from Lwamunda Swamp, Uganda. We included additional CT_max trials under low dissolved oxygen concentrations (0.20–0.50 mg/L) to test for potential interactive effects between body size and hypoxia on upper thermal tolerance. Body size did not affect C. liocephalus upper thermal limits, as small and large individuals had similar CT_max values. CT_max values decreased under hypoxic conditions but were similar across a range of body sizes. The agitation temperature (temperature during the CT_max trials when individuals appeared to become agitated, likely avoidance behaviour) was positively related to body size. This suggests that smaller individuals may be more thermally sensitive than larger fish in terms of their behavioural response to acute temperature increase.

This study aimed to understand the ecological relationship among burbot Lota lota, brown trout Salmo trutta and lake trout Salvelinus namaycush, with a focus on burbot, a species of greatest conservation need in Wyoming. While we hypothesised a reciprocal intraguild predation dynamic, where competition and predation occur between predators based on size or age structure, our findings provided limited support for this hypothesis. Both dietary overlap and trophic position were minimal among burbot, brown trout and lake trout. Instances of reciprocal predation were rare; no predation between burbot and lake trout was observed; and brown trout was the only species consumed by all predators (burbot 0.02 mean proportion by weight; lake trout 0.09 mean proportion by weight). Predation by brown trout on burbot was negligible, contributing only 0.01 to the mean proportion by weight and frequency of occurrence. Additionally, both burbot and brown trout were less piscivorous than expected, with fish comprising 0.36 and 0.17 of their mean proportion by weight in their overall diets, respectively. Overall, our findings suggest that these predators coexist with limited competitive or predatory interactions, likely due to differences in prey selection.

Understanding how the environment shapes species distribution and affects biodiversity patterns is important in ecology and conservation. Environmental stressors like climate change and anthropogenic impacts may lead to a significant decline in aquatic biodiversity. Therefore, it is imperative to characterise the current community structure and explore environmental drivers that may be important for the future community structure, also in biogeographic areas that are largely outside of the main research focus. We investigated how fish species abundances in the Karun River basin, southwest of Iran, respond to environmental predictors along a longitudinal gradient of 108 sampling sites using Generalised Linear Latent Variable Models (GLLVMs). We evaluated the response of 46 fish species to seven environmental predictors and interpreted the bivariate species co-occurrences in the residual covariance matrix in the light of potential biotic interactions. The latent variable model explained 62% of data variability in fish abundance. We identified temperature as the most important predictor, with alien species responding positively to warmer conditions, suggesting potential distribution shifts due to climate change. In contrast, endemic species showed negative responses to higher temperatures, highlighting their vulnerability. Fish abundance responses to total nitrogen concentration and average precipitation were generally negative, indicating threats from nutrient enrichment and changing rainfall patterns. There were a few systematic negative co-occurrences between alien and native fish species, which may reflect both differing environmental preferences and potential negative interactions. The model showed high predictive accuracy for the occurrence of native species, while accuracy was lower for endemic and alien species, likely due to their more limited geographical distributions. This study contributes to the global understanding of how environmental drivers shape fish communities in semi-arid river systems. By highlighting the contrasting responses of endemic and alien species to selected stressors, it provides valuable insights for predicting and managing biodiversity under climate change, offering a framework applicable to similar ecosystems worldwide.

Life history theory seeks to explain how the environment shapes life history traits. Based on this theory, we expected that Poecilia vivipara in rivers with intermittent and perennial flow regimes would show differences in maturation and reproductive investment. We sampled specimens from two rivers in the Brazilian semi-arid region with these contrasting river flow regimes. One is intermittent, where the flow ceases during the dry season and fish populations become confined to isolated pools on the riverbed, and the other is artificially perennial with continuous flow. We predicted that females would mature earlier and invest more in reproduction in the intermittent river than in the perennial river. Our findings supported the predictions; river intermittency apparently has shaped the traits of P. vivipara in natural environments as contrasted with those affected by anthropogenic alterations. Further study is needed to investigate whether these traits reflect genetic differences or phenotypic plasticity.

Declines in recruitment of lake whitefish (Coregonus clupeaformis) in the Laurentian Great Lakes have been attributed to a reduction in the amount of zooplankton prey available to young life stages, stemming from the ecosystem effects of invasive dreissenid mussels. Here, we examine the diets of two life stages of lake whitefish, the larval and post-larval stages, in relation to zooplankton availability in the environment at a historically important spawning shoal complex in Lake Huron to better understand the potential for food limitation to influence the growth and survival of these critical early life stages. The digestive tracts of larval (size range 12–26 mm) and post-larval (size range 23–43 mm) lake whitefish were extracted, and contents were identified and enumerated to describe feeding strategies and calculate electivity indices to assess selection for specific prey groups and sizes. We found that the amount of food consumed varied among years and there was an ontogenetic shift in feeding strategy, with larval fish having a more generalist diet than post-larval fish. The most important prey items were calanoid copepods for larvae and copepods and adult/pupa staged dipterans for post-larval fish. Zooplankton densities in the environment were often low, variable among years, and mostly comprised of the smallest zooplankton taxa, nauplii, which were the least preferred prey group of larval fish. The peak in zooplankton density was variable among years, including being absent, and occurred after the peak of larval abundance. Thus, it is possible that low zooplankton availability is increasing the scope for food limitation and contributing to recruitment variation in this population.

Large main stem rivers typically provide a variety of mesohabitat types, but their abundance, distribution and role in providing habitat for juvenile salmonids have rarely been analysed. The quantity of meso-scale habitats and their juvenile Atlantic salmon abundance was surveyed in the large sub-arctic River Teno in northernmost Fennoscandia. Different habitat types were mapped using the Norwegian Mesohabitat Classification Method (NMCM). Juvenile salmon abundance in different mesohabitats, on various substrates, depths and lateral positions across the channel was estimated by electrofishing boat surveys. Most of the Teno main stem (67%) was dominated by fine substrate and > 50 cm s⁻¹ flow velocity. Typical juvenile salmon-rearing habitats, such as rapids, riffles and glides, comprised 32% of the riverbed. Data from NMCM and electrofishing surveys were used in generalised linear models to describe the relationship between habitat variables and juvenile salmon (YOY and parr) abundance. Juvenile abundance varied a lot across and within mesohabitats; in general, abundance was higher in areas with depth ≤ 70 cm than in deeper areas, and in middle sections of the river compared to those near shorelines. Juvenile salmon were documented also in sandy areas, although in low abundances, and in relatively high abundances in areas deeper than typically considered important for juvenile salmon. These areas should be considered in assessing habitat potential for juvenile salmon production. NMCM proved to be a fast, cost-effective method for surveying large areas for habitat assessment.