Ecology of Freshwater Fish最新文献

Genetic differentiation in aquatic systems is often driven by geographic distance (isolation by distance) due to the linear and hierarchical distribution of populations, but habitat fragmentation often exacerbates this effect by decreasing population connectivity, leading to isolation by resistance. Stronghold populations of the Kentucky Arrow Darter (Etheostoma spilotum) in the South Fork Kentucky River system within the Daniel Boone National Forest of eastern Kentucky, USA have a high population structure not explained by distance alone. Higher than expected levels of genetic differentiation among proximate populations were hypothesized to be driven by land-use change, but this was not previously tested. Here we use a riverscape genetics approach to test for the effects of natural landscape features including slope, elevation and stream size, and anthropogenically altered habitat features, including specific conductance (conductivity), culverts and forest cover, on population connectivity and genetic diversity of E. spilotum. We found isolation of populations among all tributary systems and a strong, positive relationship between genetic and geographic distances as expected. However, high conductivity levels due to surface coal mining best explain the population structure observed. We also found signatures of low genetic diversity overall and indicators that culverts may limit upstream movements of E. spilotum. This study provides a novel fine-scale view of the effects of instream and landscape features on connectivity among, and genetic diversity within populations of an imperilled, small-bodied, benthic fish.

Dams fragment streams, alter hydrology and habitat, and facilitate establishment of nonnative species worldwide to the detriment of native biota. Understanding and mitigating these effects to conserve and restore stream fish assemblages has relied on short- and long-term datasets to assess acute and chronic change through time, craft management strategies, and measure remediation success. We used sampling records collected over a 29-year period (1993–2021) to examine likely causes of fish assemblage change in the Cache la Poudre River, Colorado, USA. Numerous low-head dams have reduced connectivity and altered flow, temperature, and habitat in the transition zone, a reach that historically supported rare and sensitive taxa valuable to regional biodiversity. We found diversity, distribution, and abundance of native species declined since the early 1990s, with formerly rare taxa extirpated and some common species becoming rare. Native taxa remained numerically dominant in warmer downstream reaches most affected by streamflow diversion but were incrementally reduced in richness and abundance upstream of low-head dams without fishways. Concurrently, nonnative Brown Trout Salmo trutta increased in distribution and abundance, dominating upstream reaches that receive cooler and more stable flows, and expanding into downstream reaches where they were formerly absent, with likely negative consequences for native fishes. In the absence of mitigation, these collective effects, plus recent wildfire disturbance and future water development, will continue to degrade stream fish assemblages in our study area, and worldwide, where resource managers face the often-competing interests of conserving native species, providing recreational fisheries, and meeting increasing water demands.

Fishes exhibit a diverse range of traits encompassing life-history strategies, feeding behaviours and spawning behaviours. These traits mediate fish population responses to changing environmental conditions such as those caused by anthropogenic stressors. The Conasauga River, located in northwestern Georgia and southeastern Tennessee, USA, hosts a diverse assemblage of over 75 species of freshwater fish, some of which are locally or regionally endemic, and many of which are imperilled. Annual monitoring data have shown population declines in multiple fish species of conservation concern in the Conasauga River since at least the 1990s, raising the possibility that other taxa could be declining as well. We quantified temporal changes in fish communities at six shoal sites sampled annually in most years from 1996 to 2022, and asked whether species traits hypothesized to underlie population vulnerability to environmental alteration were correlated with species-specific trends for 32 taxa. We estimated that total counts of fish in annual samples declined by ~2% per year, although declines were uneven among species and generally greater for less abundant taxa. Tests for species traits corresponding to temporal population trends provided evidence that crevice-spawning minnows and smaller-bodied taxa had steeper declines compared with broadcast spawners and larger, longer-lived, more fecund taxa. Lower abundance, reliance on a particular habitat feature, and life-history traits that may limit population resilience to disturbance may all prove useful for identifying riverine fishes at particular risk of future population decline.

The floodplain lakes of the Amazon constitute one of the most important aquatic systems in terms of fish biodiversity. These ecosystems are influenced by the flood pulse, which in turn, affects the behaviour of fish communities within this lake ecosystem. In this study, we tested the hypothesis that the facets of taxonomic and functional diversity may be influenced by the conditions of ‘patches’ of internal habitats, considering the margins and central environments of a floodplain lake in the Amazon. Lake Cujubim, located on the right bank of the Madeira River, was evaluated via fisheries carried out in the high-water and low-water phases, during the day and night, and considering two location strata. The results suggest that the absence of significant differences in alpha taxonomic diversity between the two phases may be a possible seasonal mischaracterisation in Lake Cujubim attributed mainly to dam constructions along the Madeira River. Apparently, no major differences occur in the assembly of fish in terms of their taxonomic and functional characteristics, regardless of luminosity. In the strata of the locations, demonstrates noticeable habitat patches, with the margins being bioregions with high incidences of individuals of the Engraulidae family, confirmed by both taxonomic and functional diversity (alpha and beta). It can be seen that, even in connected lakes, there are differentiated metacommunities between the bioregions, thus forming patches of habitat, and that the shores of the lake, especially those located in proximity or distant from the river, are more suitable areas for food and refuge.

An increasing presence of instream structures such as weirs, dams, culverts and reservoirs degrades habitats, fragments rivers and blocks fish movements worldwide. Longitudinal river movements are fundamental for many fish species and the most widespread solution to restore longitudinal connectivity is the implementation of different fish passage solutions. Fishway functionality, however, is highly variable. To design a functional fishway, several aspects of the fish's interaction with its environment need to be taken into consideration. Artificial light at night (ALAN) can affect a range of different behaviours in fish, from activity and movement to feeding and predator–prey relationships. In a fish passage setting, fish are exposed to artificial light at night (ALAN) in the form of light pollution, but, sometimes, also as part of the fish passage solution. Although likely highly species specific, the effect of artificial light on fish passage behaviour has been little explored. Here we study the passage behaviour of two small-sized fish species, European gudgeon (Gobio gobio) and Italian riffle dace (Telestes muticellus), over a scaled deep side notch weir in a hydraulic flume in three different light conditions: daylight, darkness and ALAN. Although both species passed the obstacle at high efficiencies under all light conditions, their passage behaviours were influenced by light, particularly at the higher levels. While ALAN reduced passage success and resulted in delayed passage for gudgeon, riffle dace passed at higher rates under the artificial light compared to night treatment. Both results indicate a risk of negative effects from ALAN on passage performance at real fishways—or movement rates in lit areas of natural streams—for both species. Independent of light conditions, individuals of both species also passed faster after repeated trials, demonstrating learning in a fish passage context.

Headwaters are important refuges for threatened fishes and play an important role in their conservation. The effects of large flooding events on headwater fish assemblages are under studied in southern Africa. In January 2012, heavy rainfall resulted in a large flood in the upper Klaserie River, Olifants River, and Limpopo River System, South Africa. This flood had an estimated return level of 225 years and caused significant ecological and economic damage. This study aimed to explore the impact of a large flood on the fish assemblage and substrate in the headwaters of a subtropical stream. The fish communities and selected substrate variables were collected at 10 sites. Sites were sampled at six monthly intervals thrice before and thrice after the flood. Fish were collected by electrofishing and substrate quantified visually. Changes in habitat resulted from the flood included the scouring of gravel sand and mud, greater exposure of bedrock and boulder substrates, increased stream width, and decreased stream depth in all zones. The fish community showed an increase in abundance for all but three species, colonisation of upstream sites, and colonisation of the study area by six species. The majority of fish species have opportunistic life-history traits, which could explain the rapid colonisation and increase in abundance. The flood occurred in the middle of the breeding season for most the fish species, and this resulted in an increase of abundance for these species and provided opportunities for upstream colonisation. The impact of late season and aseasonal large floods requires further study.

Understanding environmental requirements for fish reproduction in natural habitats is crucial for population conservation and restoration. However, such information is extremely scarce for the highly threatened schizothoracine fishes that cover large elevation ranges on the Tibetan Plateau. This research investigated the spawning time, output and environmental conditions of wild Schizopygopsis thermalis along an elevational gradient (i.e., from 1766 to 4372 m) in the upper Nu-Salween River. It found that the spawning grounds of S. thermalis were mainly located at elevations between 3600 and 4372 m, and spawning habitats mostly consist of still marginal areas (still water <10 cm deep) with gravel substrates. Otolith microstructure analysis revealed, for the first time, that S. thermalis spawns in two seasons (i.e., winter: from December to next February, and spring: from April to May), with the winter spawning period generally longer than the spring spawning period. Winter spawning started earlier and ended earlier at higher elevations, while spring spawning occurred earlier at lower elevations but ended simultaneously at higher elevations. As elevation increases, reproductive output also increases, and spawning cohorts shift from winter-dominant to spring-dominant. Winter spawning cohorts were associated with lower water temperatures but higher discharges than the spring spawning cohort, and both cohorts showed elevation-related environmental preferences. Our results suggest that schizothoracine fish can adapt spawning strategies to elevation-related environmental conditions, which fill the gaps in the reproductive characteristics of schizothoracine fishes, and highlight the importance of conserving schizothoracine habitats at high elevations in the Qinghai-Tibetan rivers.

Discharged floods containing a large amount of suspended sediment (SS) can lead to total dissolved gas (TDG) supersaturation downstream of dams. The swimming ability of fish may be affected by TDG supersaturation and excessive SS. However, previous studies focused only on the separate effects of TDG and SS, ignoring their combined effects. In this study, juvenile rock carp and grass carp were selected to assess the interactive effects of TDG and SS on fish swimming ability. A totally crossed two-factorial design (six TDG levels: 100%, 115%, 120%, 125%, 130% and 135%; four SS concentrations: 0, 50, 100 and 150 mg/L) was set, and the critical swimming speed (U_crit) and the burst swimming speed (U_burst) were measured. The findings indicated that the swimming abilities (U_crit and U_burst) of both fish species decreased with increasing TDG levels and SS concentrations. Separate exposure to TDG significantly decreased the swimming abilities of the two fish species, whereas separate exposure to SS decreased only the swimming abilities of juvenile grass carp. Juvenile rock carp exhibited weaker swimming abilities than juvenile grass carp in TDG-supersaturated water. Additionally, the interaction between TDG and SS reduced the swimming abilities of juvenile rock carp and grass carp compared with a separate effect, but this reduction was significant only for the U_crit of juvenile grass carp. This study demonstrates that TDG-supersaturated water containing SS during flooding may result in fish failure through fishways.

Spawning migrations of fishes are common case studies for examining the magnitude of resource subsidies; however, no studies have evaluated this phenomenon in iteroparous migrations of the Catostomid (i.e. suckers) genus Moxostoma (i.e. redhorses). Fish resource subsidies are usually represented as nitrogen (N) and phosphorus (P), and migratory redhorses can deliver these nutrients via excretion and eggs. We evaluated whether redhorses deliver N and P subsidies to Brasstown Creek—a fourth-order stream in the Southeastern US—during their spawning migrations. We measured individual-level nutrient contributions from excretion and eggs and extrapolated those values to estimate nutrient contributions based on daily abundances of migratory redhorses. We compared daily nutrient inputs to daily nutrient exports to determine the potential for resource subsidies. We estimated 71.6 kg of N and 4.4 kg of P were delivered to Brasstown Creek over a 98-day migration period. N input exceeded N export on 15 of the 98 days, but phosphorus input never exceeded P export. Eggs accounted for the majority of N and P input at 51% and 100% respectively. Redhorse N inputs peaked in the spring during a period of low N exports, suggesting that redhorse subsidies were delivered during times of elevated nutrient demand and relatively low nutrient availability. Suckers receive little management attention, and several species of redhorses are imperilled. Given our conclusion that redhorses provide a temporally critical N subsidy that is likely available to multiple consumers in freshwater food webs, this study provides compelling motivation for increased conservation of these species and their migrations.

Male chum salmon display a courtship behaviour involving an actively “quivering” against female, which is essential for female orgasm. Because generally male prefer larger female, we determined whether the elements of quivering such as the number, the amplitude, and the distance are affected by female body size. Additionally, quivering changes towards oviposition; therefore, we also identified the essential time for the male to succeed in his courtship behaviour. We conducted two experiments to measure quivering parameters: (i) measuring the number and the amplitude of quivering by the acceleration data logger and (ii) measuring the distance between sexes during quivering by observation of recorded video. From the first experiment, there was no significant relationship between the ratio of female-to-male body lengths and the number and the amplitude of quivering, while an important relationship between the body length ratio and the distance between sexes from the second experiment. Therefore, we think the distance is more significant than the number or vigour of quivering for male choice, and males quiver more closely to a larger female to increase reproductive success. In addition, when the body length ratio of the sexes is 1.01, the distance during quivering is the shortest. So, there is a possibility that the reproduction of chum salmon is based on size-assortative mating. And both experiments also showed that male quiver passively as spawning approaches. We suggest that males may not quiver actively for smooth mating as females spawning approaches.