Initial weight and its variation in post-larval Eurasian perch affect quantitative characteristics of juvenile cohorts under controlled conditions

Abstract

Eurasian perch larvae originating from a single father and three mothers were reared under different stocking densities for 16–19 days post-hatch. Then, a 84-day experiment was conducted to determine the effect of initial post-larval average weight and its variation on further quantitative juvenile cohort characteristics. Groups of 800 fish were composed of either siblings only (A, B, C) or half-sibs (A+B, A+C, B+C, A+B+C evenly). Progeny A was significantly bigger at the start of the experiment (day 0), and variation in their weight was significantly higher than in B or C. During the experiment, increase in average weight was 650-fold, from 0.007 g (day 0) to 4.56 g (day 84). The two factors: initial post-larval average weight (W0) and variation in weights (CV0) affected, in different ways, further stock characteristics: average weight, survival and biomass. W0, but not CV0, negatively affected specific growth rates in the initial phase. CV0, but not W0, positively affected type II cannibalism, which was the most important reason of mortality. Current average weight was positively affected by type II cannibalism until day 42 and by W0 until day 63, after which emerging effect of stocking density inhibited average growth. No sex-related effects on growth were observed. Variation in weight showed no relation with other variables. Mixing progenies on day 0 of the experiment did not affect final growth variables. The study demonstrates that initial post-larval W0 and CV0 significantly affect growth and survival of juveniles cohorts, even those consisting of siblings. A model of multiple relations between tested variables is proposed.