Trophic consequences of an invasive, small-bodied non-native fish, sunbleak Leucaspius delineatus, for native pond fishes

Assessments of the trophic consequences of invasive fishes are important for quantifying their ecological impacts on native species more generally. A small-bodied cyprinid fish native to continental Europe and introduced in the 1970s to the U.K, the sunbleak Leuciscus delineatus, has been shown previously to establish closer social associations with native species of similar size than do native species amongst themselves. To assess the potential detrimental trophic consequences of native species associations with L. delineatus, a field-based experiment was undertaken in summer 2015 in six outdoor, artificial ponds containing three native cyprinid species (rudd Scardinius erthrophthalamus, gudgeon Gobio gobio, tench Tinca tinca). Three ponds were controls (no L. delineatus) and three were treatments (L. delineatus present). The results of stable isotope analysis (SIA) of fish tissue samples provided strong evidence that the isotopic niches of both native benthic fishes were reduced in the presence of L. delineatus, although there were no significant effects on the trophic position, body size or condition of two of the three native fish species. Introduced L. delineatus maintained a core isotopic niche that was distinct from the two native benthic fishes, with no overlap detected between native and non-native fishes when including 40 % and 95% of the data. These results indicate that the response of the native fishes to the introduction of L. delineatus was niche constriction via trophic specialisation, with this response sufficient to maintain their growth rates and condition. This result is similar to studies on a range of small-bodied invasive fishes, suggesting the trophic impacts of these invaders are relatively consistent across species and systems

Trophic interactions in a lowland river fish community invaded by European barbel Barbus barbus (Actinopterygii, Cyprinidae)

Following their invasion, non-indigenous fish can potentially exclude native fishes from their original niches through competition, or can partition in their resource use with native species to facilitate co-existence. Here, using stable isotope analysis, the trophic interactions of invasive European barbel Barbus barbus and other fishes were tested in an invaded river of relatively low fish species diversity and where no other Barbus species were present. Testing was over three distinct life stages: age 0 + ( 386 mm). There were strong patterns of isotopic niche partitioning between the juvenile fishes, with some inter-specific niche differences also apparent in 0 + fishes. For adult B. barbus and chub Squalius cephalus, however, niche convergence was evident. Within the B. barbus population, the niches of the adult fish differed significantly from the 0+ and juvenile fish, indicating considerable dietary changes with development. These results suggested that niche partitioning at the most abundant life stages were facilitating the co-existence of invasive B. barbus with other fishes in the community, with this most likely driven by inter-specific differences in functional morphology and habitat use