Abstract
A study was carried out on lysozyme activity and spontaneous haemolytic (SH) activity of blood serum from 388 individuals of Nile tilapia ( Oreochromis niloticus) coming from 42 full-sib groups within 21 paternal half-sib groups. The lysozyme activity was measured at both 15°C and 30°C incubation temperatures, whereas SH activity was measured at 30°C incubation temperature. Significant variation in lysozyme activity was detected between half-sib groups at 30°C incubation temperature, but not at 15°C incubation temperature and not for SH activity. Significant variation was found between full-sib groups for all parameters. The estimated heritabilities of lysozyme activity were relatively high (0.6–0.7) at 30°C incubation temperature and intermediate (about 0.3) at 15°C incubation temperature. The heritability estimate of SH activity was zero according to estimates based both on the sire component of variance and on variance components from an individual animal model, whereas the estimate based on the dam component of variance was about 0.7 and highly significant. Survival and growth were recorded after a grow-out period of 120 days in individuals from a parallel set of samples from the same sib families. Significant negative correlations were found between least-squares means in the parallel sib groups for lysozyme activity and survival rates for both half-sib groups ( r=−0.53; P=0.01) and full-sib groups ( r=−0.32; P=0.04). No significant correlations were found between SH activity and survival rate nor between lytic activities and body weight at harvest.
Published Version
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