Two immunogenetical parameters in five Danish rainbow trout (Oncorhynchus mykiss) strains and their relation to body weight

The distribution of different phenotypes of the complement component C3 and a possible correlation with body weight were investigated in five Danish strains (A, C, D, E, J) of farmed trout (Oncorhynchus mykiss Walbaum). All strains showed the presence of the f1 and f2 alleles; two of these strains also expressed the s allele.

Most common was the fl allele (> 68%); rarest was the s allele (<9% or absent). In the J strain, a significantly higher frequency of the f1 allele was observed. Only in the D strain was a linkage indicated between the mean values of body weight of trout and different C3 phenotypes (P = 0.002); the mean body weight of individuals with the f1 phenotype was also lower than that of the f1/f2 and s/f1 phenotypes.

This result, however, is not conclusive, as it was observed in only one of the five strains and because the number of individuals in some of the phenotype groups was very small. The reactivity of monoclonal antibody Hyb106-1 that reacts with a carbohydrate epitope on the serum immunoglobulin molecule was also investigated in the five rainbow trout strains.

The percentage of positively reacting trout sera varied from 9% to 43%. In the D and the E strains, positive individuals showed a significantly (P = 0.036, resp. P = 0.005) lower body weight than did the negative individuals. No linkage between the reactivity with monoclonal antibody Hyb106-1 and the f1 and f2 alleles of complement component C3 was observed.

However, individuals that reacted negatively with the carbohydrate marker expressed only the s allele, possibly caused by a low number of samples expressing the s allele.