The aim of this study was to assess whether size-rank at the juvenile stage is associated with growth performance and sex ratio in olive flounder (Paralichthys olivaceus). Juveniles (mean body weight, 8.8 +- 0.9 g) were selected from two age groups, with the high size-rank group (HSRG) fish in the upper 19.3-67.3 of 104 days post-hatching (dph) age group and the low size-rank group (LSRG) fish in the lower 9.0-55.7 of 116 dph age group. Triplicate groups of 100 fish were reared over 32 weeks. A heavier final body weight was observed in the HSRG (360 +- 12 g) compared to the LSRG (315 +- 9 g, P<0.05), whereas no differences in feed intake, feeding efficiency, and mortality were seen between the experimental groups. The percentage of females was significantly higher in the HSRG (51.7) than in the LSRG (30.8, P<0.05). In addition, a remarkable increase in growth was recorded in females, indicating that the relative frequency of females increased with a body weight increase. The results suggest that high size-rank juvenile olive flounder have better growth performance and a higher percentage of females, because females start growing faster than males before size grading occurs.
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