Ecology of Freshwater Fish最新文献

Conservation and effective management of freshwater ecosystems require detailed insights into species-specific dietary strategies, resource partitioning and ecological interactions, including competition for shared resources. This study investigates seasonal dietary shifts within four barbel species (Atlantor reinii, Luciobarbus magniatlantis, Luciobarbus ksibi and Carasobarbus fritschii) in the Zat Basin (Morocco). The study's objective is to inform conservation and ecosystem management planning that should be considered for threatened species, such as A. reinii and L. magniatlantis. We evaluated feeding strategies and niche partitioning across species and seasons using stomach content analysis and alimentary indices, including Dietary Index (DI) and occurrence (OC). L. ksibi demonstrated the highest insect consumption (OC = 51.11%, DI = 0.84%). L. magniatlantis showed the most diverse animal prey composition, with the highest Mollusca occurrence (OC = 76.67%, DI = 0.59%), substantial insect intake (OC = 54.07%, DI = 1.43%) and significant Arachnida presence (OC = 60%, DI = 0.54%). A. reinii displayed the highest selectivity for insects (DI = 1.14%). C. fritschii exhibited moderate insect consumption (OC = 36.30%, DI = 0.88%) and an equal preference for Mollusca and Tubellaria (both OC = 53.33%, DI = 0.38% and 0.64%, respectively). NMDS analyses revealed partial dietary overlap among species, with A. reinii and C. fritschii exhibiting distinct clustering, while L. ksibi and L. magniatlantis displayed broader nutritional niches. Moderate-to-high dietary niche overlap, particularly between C. fritschii and L. ksibi, highlights the potential for significant competition for shared prey resources, which may intensify during periods of resource scarcity. This study highlights species-specific dietary flexibility, emphasising the importance of adaptive foraging strategies in conservation planning and the ecological resilience of freshwater fish in Mediterranean streams.

Invasive species are among the biggest threats to biodiversity and represent billions of dollars to the global economy. Invasive species pose a threat to the biodiversity of freshwater ecosystems, which are among the most vulnerable due to their isolation by terrestrial ecosystems and the impact of human activities. While invasive species in freshwater ecosystems are known to cause extinctions and therefore reduce species richness, little attention has been paid to their effects on functional richness. Here, we aimed to evaluate the species and functional richness of a wetland fish community that has been subjected to the introduction of exotic species in repeated events over four decades. Our study site, La Mintzita, was home to 15 native species, some of them endemic to the Central Mexican Plateau; the ongoing changes in the fish community have led to a current state where the richness of invasive species matches that of native species. Over the decades, functional richness has declined, dropping from 8.1 before 1985 to 2.8 in the 2020s. We found that in the 2020s, functional richness was significantly lower than expected by chance. The native species that might be locally extinct are those occupying similar functional niches as the invaders or those that are the most sensitive, thus indicating a process of fauna homogenisation. We highlight the importance of focusing conservation efforts on maintaining functional richness to preserve services derived from freshwater ecosystems.

Migrating animals are found throughout the animal kingdom, as movement between habitats can be vital for survival, growth, and reproduction. Mature sea trout (Salmo trutta L.) undertake seasonal migrations from marine feeding areas to freshwater spawning habitats, but the migration dynamics may vary considerably between rivers of different morphology and location. In this study, we used radio-telemetry with multi-year tags to observe the riverine movements and spawning migration behaviour of wild sea trout tagged in a large, northern Baltic Sea river system, the Tornio River. Both immature and mature trout were observed to have similar overwintering behaviour as they mainly overwintered in the same locations in the lower river. Many immature trout returned to overwinter for multiple consecutive winters without spawning, a behaviour that has been rarely reported for sea trout in rivers of the northern Baltic Sea. The results from a support vector model highlighted the importance of trout age and previous spawning experience for the direction of the migration, as previously spawned and older trout were more likely to migrate upstream for spawning while their younger counterparts returned to sea in summer after spending the winter in freshwater. The riverine movement patterns indicate that the majority of mature sea trout migrating upstream for spawning in the river system have adopted a spawning migration strategy, which extends for almost two calendar years. Mature sea trout enter freshwater in autumn the year prior to spawning, migrate to spawning habitats and spawn in the year following freshwater entry, and overwinter in-river for a second time post-spawning. This migration strategy has not been previously reported for sea trout native to Baltic Sea river systems. The extended freshwater stays and numerous migrations between sea and river habitats in large, high-latitude rivers need to be considered in management to ensure adequate protection of both immature and mature sea trout.

Introduced species are one of the biggest threats to aquatic ecosystems. Rainbow trout (Oncorhynchus mykiss, Salmonidae) is considered one of the most dangerous introduced predatory fish species, as they often put native species at risk of extinction. This study evaluated the effects of rainbow trout introduction on Andean stream food webs. We tested the hypothesis that the presence of rainbow trout changes Andean stream food webs by changing the diet of other carnivorous species and the energy source supporting native fish species. We sampled streams with and without rainbow trout and with different vegetation cover (i.e., pastures and crops versus forest) and combined data from stomach contents and stable isotopes. We analyed stomach contents from 231 specimens of two native catfish species and 116 rainbow trout specimens. Our results demonstrate that aquatic insects are essential in Andean stream food webs, where collector gatherers and scrapers were the most consumed and assimilated by catfish and rainbow trout species. Leaf litter was predicted to be the primary energy source in streams with forest cover. In contrast, periphyton contributed the most in streams with pastures and crops. We conclude that the presence of trout coupled with use/land cover (i.e., vegetation cover) exerts a substantial effect on Andean stream food webs. Protection of riparian forests of the Andean streams of Colombia is needed to guarantee the stability of aquatic food webs and thus help native species coexist with established non-native species introduced decades ago.

Understanding patterns of trophic niche overlap in fish communities is important because trophic redundancy can stabilise food webs. δ¹³C and δ¹⁵N in fish can be converted into percent littoral carbon and trophic position, respectively, and subsequently used to estimate isotopic niche size and overlap between species. We hypothesised yellow perch (Perca flavescens) would have the most niche overlap on other species due to their central position in lake food webs and large ontogenetic changes in diet. We also hypothesised variance in niche overlap across lakes would be driven by variance in size structure of perch populations among lakes. Alternatively, variance in perch niche overlap could be driven by food web variables such as mean trophic position. We addressed these questions by sampling fish in 17 Minnesota (USA) lakes. Results showed mean perch niche overlap on other species was significantly larger than all other species, and that perch niche size was positively related to niche overlap. We subsequently found no evidence perch population length structure influenced niche size or overlap, as no metrics of perch size structure were related to either variable. Instead, perch mean trophic position was negatively related to perch niche overlap and marginally related to niche size. Perch mean trophic position, in turn, was positively related to depth of hypoxic water. Our results indicate yellow perch may be important for stabilising lake food webs through high trophic redundancy on other fish species and that the degree of trophic redundancy may be influenced by dissolved oxygen patterns in lakes.

Many aspects of the ecology, life history and distribution of fishes differ between their larval and adult life-history stages. Identifying the critical habitats and migration pathways required by each life cycle stage is crucial for effective conservation and ecological management. Using microchemical analysis of otoliths, we examined the influence of larval habitat and migration on the composition and population structure of migratory and nonmigratory Galaxias species collected from tributaries upstream of inland lakes and streams lacking downstream lake connections in the Waitaki River basin, New Zealand. Larval (core) and adult (edge) layers of each individual otolith were analysed to compare otolith trace signatures formed during larval and adult life-history stages. The results revealed considerable variation between larval and adult otolith chemical signatures of migratory (Galaxias brevipinnis) species. Classification analysis indicated that populations of G. brevipinnis upstream of each lake shared a common larval habitat, most likely the lake, with 100% of individuals from each lake-riverine system having larval signatures that were distinct from adult signatures. In contrast, relatively consistent patterns of elemental concentrations were detected across the otoliths of nonmigratory species suggesting both their larval and adult life-history stages had occurred in the same stream from which the adults were collected. These findings provide a framework for understanding how larval-rearing environments can influence the distribution of stream fish across the landscape. Furthermore, identifying the source of recruits can help to improve conservation efforts to protect naturally land-locked populations of G. brevipinnis.