Gape-size dependent feeding of age-0 perch (Perca fluviatilis) and age-0 zander (Stizostedion lucioperca) on Daphnia galeata
Mehner, Thomas; Plewa, Matthias; Hülsmann, Stephan; Worischka, Susanne
published: May 26, 1998
ArtNo. ESP141014202008, Price: 29.00 €
Based on fish consumption estimates, the midsummer decline of Daphnia has been attributed frequently to predation by age-0 fish. From studies on food selectivity, however, little evidence exists that small, gape-limited age-0 fish strongly influence Daphnia populations. Therefore, we measured gape sizes and compared gape-size dependent feeding in age-0 fish of two related percid species, perch (Perca fluviatilis) and zander (Stizostedion lucioperca). We sampled fish and Daphnia in the biomanipulated Bautzen reservoir (Germany) during spring and early summer over 2 years. The small gape size of newly hatched fish prevented predation on daphnids until mid-May. Later, feeding intensity on daphnids by fish (expressed as the index of relative importance IRI) closely corresponded to the Daphnia density, independent of gape size of fish. However, the gape size of fish predicts both species-selective and size-selective feeding on daphnids in perch and zander. Only perch and zander > 20-25 mm TL fed on larger-than-average daphnids and positively selected daphnids, independent of Daphnia density. Although growth of fish and Daphnia densities differed between both years studied, slopes and intercepts of the linear relationships between gape size and selectivity for daphnids did not differ. Consequently, only in those years in which age-0 fish are sufficiently large to consume large, mature Daphnia in early summer, can we expect a midsummer Daphnia decline.