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

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, Q 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 (W-0) and variation in weights (CV0) affected, in different ways, further stock characteristics: average weight, survival and biomass. W-0, but not CV0, negatively affected specific growth rates in the initial phase. CV0, but not W-0, 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 W-0 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 W-0 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. (C) 2004 Elsevier B.V. All rights reserved.