Genetic polymorphism of complement component C3 in rainbow trout ( Oncorhynchus mykiss) and resistance to viral haemorrhagic septicaemia

Abstract

A possible relation between alloforms of complement component C3 in rainbow trout ( Oncorhynchus mykiss) and resistance to viral haemorrhagic septicaemia was investigated by testing alloform and phenotype frequencies in different fish farm populations. Fish farm A, a non-infected production farm, supplied fry to the infected fish farm B and the non-infected fish farm C. Surviving trout of the infected fish farm B differed significantly ( P<0·05) from fish of the non-infected farms A and C with respect to the distribution of the investigated alleles f1 and f2. The f2 allele was found in a significantly lower frequency in the infected fish farm. However, a postulated relation between certain phenotypes carrying the f2 allele could not be confirmed by testing phenotype frequencies in the different fish farms by a χ 2-test. The distribution of phenotypes in fish farm C was not in agreement with that predicted from allele frequencies by the Hardy-Weinberg equation, suggesting the existence of other, unknown, selective forces affecting the phenotype distribution.