Genetic variation in lysozyme activity in rainbow trout ( Oncorhynchus mykiss)

Lysozyme activity in blood was analysed in full- and half-sib families of rainbow trout, Oncorhynchus mykiss. 1075 fish from 80 full-sib groups within 30 paternal half-sib groups were sampled. The elapsed time between the initial crowding of fish for blood sampling and the collection of a blood sample from a particular fish, affected the lysozyme activity significantly. Statistically significant effects of sire on the lysozyme activity provide evidence of significant additive genetic variation in lysozyme activity in rainbow trout. The estimated heritabilities of the lysozyme activity were in the order of 0.2–0.3 with a standard error of approximately 0.05–0.15. Production parameters, such as mean weight at slaughter and mean survival during the sea-rearing period, were obtained for fish which were reared commercially and which belonged to the same full-sib groups as those analysed for lysozyme activity. The correlations between least squares means of lysozyme activity and production parameters, based on the full-sib records, were not significant.