Individual heterozygosity levels and relative growth performance in Oreochromis niloticus (L.) cultured under Fijian conditions

Tilapia (Oreochromis spp.) (Pisces: Cichlidae) are important freshwater fis hes that are widely cultured worldwide and have been introduced to the Fiji islands as an aquaculture resource. An O. niloticus (L.) 'Chitralada' stoc k cultured under Fijian conditions was studied to assess the potential of u sing individual multilocus heterozygosity as an indicator of relative growt h performance. Allozyme analysis was undertaken in each of three generation s (n = 50/generation) of 'Chitralada' grow-out. Subsequent correlation and regression analysis of 25 allozyme loci with individual body weights demons trated no significant association between individual heterozygosity and gro wth rate in any of the generations. Correlation analysis between heterozygo sity based on nine microsatellite loci screened in a subset of 'Chitralada' individuals (n = 43, generation 2) and morphological measurements, demonst rated a significant relationship between heterozygosity at locus UNH146. Ho mozygous individuals at this locus were characterized by larger lengths and weights than heterozygotes. No significant correlations with either length or weight were observed at any of the other eight microsatellite loci. Sel ecting broodstock therefore based solely on individual allozyme or microsat ellite heterozygosity levels is unlikely to increase relative growth perfor mance in the Fijian cultured O. niloticus 'Chitralada' stock.