The effect of size sorting on rearing effectiveness in Eurasian perch post-larvae was evaluated. A 34-day-old perch were reared for 2 weeks in three experimental groups as a small size group (SM, mean weight 0.061 ± 0.011 g), large size group (SL, mean weight 0.148 ± 0.024 g), and unsorted group (US, mean weight 0.105 ± 0.048 g) in recirculating aquaculture system (21°C; 12 L:12D). At the end of the experiment, specific growth rate (% day −1) was significant greater (P < 0.05) in SM (9.48 ± 0.34) than SL (6.95 ± 0.40) and US (8.35 ± 0.60); however, significant size rank correlations (initial weight vs. final weight) were maintained in all experimental groups (r sp > 0.77). Fish biomass gain (% of IBs) were significant higher (P < 0.05) in both sorted groups 344 ± 29 and 256 ± 6 for SM and SL, respectively than US (233 ± 10), which directly resulted from higher survival in sorted groups (> 90.0%) than US (75.6%). Difference in observed survival rates resulted from significant lower losses to type I cannibalism in both sorted groups, 4.3 and 3.2% for SM and SL, respectively than in US (> 18.0%) (P < 0.05). It is concluded that the size sorting of Eurasian perch post-larvae has a positive impact on the rearing effectiveness, measured as significant higher biomass gain, directly resulting from higher survival, trough lower losses caused by cannibalism type I.

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