Relationships between feeding, growth and swimming activity of European sprat ( Sprattus sprattus L.) post-larvae in the laboratory.

Despite their trophodynamic importance in many aquatic ecosystems, few studies have quantified the feeding-growth relationship of clupeid fishes. In laboratory trials, we quantified the relationship between rates of food consumption ( C, % fish energy content (Joules d)), somatic growth rate ( G, % Joules d), and swimming speed ( S body lengths ( bl) s) for post-larval (30- to 50-mm standard length) European sprat ( Sprattus sprattus L.) collected from the southwestern Baltic Sea. Measurements of G and S were also made on groups before and after an abrupt shift in prey availability. Maintenance (0-growth) and maximum food consumption rates were 5.5 and 42 % somatic energy content d, respectively. Mean ± SE gross growth efficiency ( K = 100∙ G∙ C) was 26.9 ± 3.0 %. Unfed post-larvae had markedly lower S compared to continuously-fed fish (0.1 versus 0.5 to 0.7 bl s). After 10 days of re-feeding, one group of previously unfed fish was hyperactive (mean S of 1.2 bl s) but no re-fed groups exhibited hyperphagia (based upon prey numbers), increased K, or compensatory growth. Increased competition (relatively high S) was evident during feeding in fish maintained at low to moderate but not at ad libitum prey levels. Our findings provide estimates of prey resources required to fuel in situ growth and help characterize metabolic strategies of European sprat within variable feeding environments. [ABSTRACT FROM AUTHOR]