Lack of Response byTilapia niloticato Mass Selection for Rapid Early Growth

Mass selection for rapid and slow early growth was applied for one generation to 58-d-old Nile tilapia Tilapia nilotica (Ivory Coast strain). Realized heritability (±SE) for rapid growth was –0.10 ± 0.02, and mean body weight of progeny was not different (P > 0.05) from that of control fish. This confirms an earlier prediction from half-sib analysis of the same stock that selection for rapid growth would be ineffective for these fish (half-sib heritabilities were 0.04 ± 0.14 at age 45 d and 0.04 ± 0.06 at age 90 d). In contrast, selection for slow early growth resulted in realized heritability of 0.36 ± 0.08, and mean body weight of progeny was less than that of control fish (P < 0.05). Our study indicated that an upper limit to growth enhancement by selection exists in this stock of T. nilotica, probably due to a small founder stock, subsequent reductions in effective breeding numbers, and 8 years of domestication. We conclude that half-sib analysis can be an efficient means for estimating the effectiveness of mass selection.