Trophic consequences of non-native pumpkinseed Lepomis gibbosus for native pond fishes

Introduced non-native fishes can cause considerable adverse impacts on freshwater ecosystems. The pumpkinseed Lepomis gibbosus, a North American centrarchid, is one of the most widely distributed non-native fishes in Europe, having established self-sustaining populations in at least 28 countries, including the U.K. where it is predicted to become invasive under warmer climate conditions. To predict the consequences of increased invasiveness, a field experiment was completed over a summer period using a Control comprising of an assemblage of native fishes of known starting abundance and a Treatment using the same assemblage but with elevated L. gibbosus densities. The trophic consequences of L. gibbosus invasion were assessed with stable isotope analysis and associated metrics including the isotopic niche, measured as standard ellipse area. The isotopic niches of native gudgeon Gobio gobio and roach Rutilus rutilus overlapped substantially with that of non-native L. gibbosus, and were also substantially reduced in size compared to ponds where L. gibbosus were absent. This suggests these native fishes shifted to a more specialized diet in L. gibbosus presence. Both of these native fishes also demonstrated a concomitant and significant reduction in their trophic position in L. gibbosus presence, with a significant decrease also evident in the somatic growth rate and body condition of G. gobio. Thus, there were marked changes detected in the isotopic ecology and growth rates of the native fish in the presence of non-native L. gibbosus. The implications of these results for present and future invaded pond communities are discussed

The diet, growth and condition of common bream, Abramis brama (L.) in Włocławek Reservoir

Within 1997-1999, studies were carried out in Włocławek Reservoir to determine diet composition, growth rate, and condition of common bream, Abramis brama (L.)-the dominant fish species there. An extraordinary abundance of bottom fauna in this reservoir is the reason that already in the first year, common bream begin to feed intensively on zoobenthos, they grow very rapidly (in length and weight), and are in good condition. Literature reports that at the beginning of the 1980s, when zoobenthos in the reservoir was considerably less abundant, bream growth was slower

Malacofauna of two hydrologically different habitats in the near-shore zone of the Wloclawek dam reservoir (Vistula River, Poland)

We studied molluscan fauna at two sites in the W³oc³awek Dam Reservoir, differing with respect to the hydrological conditions: a rheolimnic site with a comparatively strong water flow (Soczewka) and a limnetic site, dominated by wave action (Dobiegniewo). Within each site, we sampled molluscs from three substratum types (sand, a thin layer of mud on sand and mud). Samples were collected monthly, from April to October. The taxonomic composition differed between the sites, with Sphaerium corneum (L. 1758), Pisidium sp. C. Pfeiffer, 1821, Bithynia tentaculata (L. 1758) and Viviparus viviparus (L. 1758) being more abundant in Soczewka, while Potamopyrgus antipodarum (Gray, 1843), Marstoniopsis scholtzi (Schmidt, 1856) and Dreissena polymorpha (Pallas 1771) occurred exclusively in Dobiegniewo. S. corneum was a strong dominant in most of the samples, and variation in its abundance was the only cause of the observed differences among the various substrata. Strong differences in the total density and biomass were also observed between the two sites, the molluscs from Soczewka being much more abundant. This phenomenon was particularly apparent on the muddy substratum, which was the most suitable in Soczewka and the poorest in Dobiegniewo. Our study revealed that moderate water flow in Soczewka affected molluscs by improving conditions for them, especially on the muddy substratum