Effect of size grading on growth, survival, and cannibalism in larval and juvenile pike, Esox lucius (L.), reared in recirculating systems.

The effect of size grading on rearing effectiveness in pike larvae and juvenile was evaluated. Three separate experiments (I, II, and III) were conducted in groups of fish with initial mean body weights of 0.047 g, 0.135 g, and 1.17 g (at corresponding ages of 29, 46, and 68 days post hatching). Before the start of each part of the experiment, the fish were graded into the following groups: small fish (group S), large fish (group L), and ungraded fish (group U). In experiment I, the mean body weights of pike in the small (SI), large (LI), and ungraded (UI) groups were 0.041 g, 0.054 g, and 0.047 g, respectively. In experiment II, the body weights in groups SII, LII, and UII were 0.098 g, 0.170 g, and 0.137 g, respectively, and in experiment III in groups SIII, LIII, and UIII were 0.99 g, 1.32 g, and 1.19 g, respectively. The stocking density in experimental I, II, and III was 450, 300, and 150 individuals per tank, respectively. Three replications were performed for each group. The duration of each experiment was 14 days and the fish were reared in a recirculating aquaculture system (20 °C, 24L:0D). The fish were fed with commercial sinking feed in the amount of 20% of the fish biomass per day in experiment I, 15% in experiment II, and 10% in experiment III. The results of the study showed that the size grading resulted in a two-fold reduction in cannibalism among large fish compared to the small and ungraded fish, which resulted in the highest survival of large pikes in experiment I. The biomass gain was significantly higher in small fish compared to large fish only in experiment III. When the growth performances obtained for the graded groups were analyzed together (groups S + L) and then compared with the results obtained for the ungraded fish (group U), only significant differences were observed in pike cannibalism for experiments I and II. The level of cannibalism in these experiments was lower in the graded fish. Ultimately, size grading does not improve the survival and biomass gain of graded fish compared to ungraded fish. [ABSTRACT FROM AUTHOR]