Comparison of growth performance, immunological response and genetic diversity of five strains of rainbow trout (Oncorhynchus mykiss)

The domestication of rainbow trout, Oncorhynchus mykiss, has led to the development of distinguishable isolated populations. In this study, five different strains of rainbow trout from the Northwest, USA were examined for variability in growth, immunological response, and genetic diversity. Growth rates for the different strains were monitored and compared for 28 weeks, with the animals fed at a fixed rate or to apparent satiation. Feed conversion ratios (FCR), specific growth rates (SGR), and thermal-unit growth coefficients (TGC) for the entire period were calculated for each of the strains. The different strains were also evaluated immunologically with infectious hematopoietic necrosis virus (IHNV), and their post-immunization antibody neutralization titers were monitored for a period of 12 weeks. Using microsatellites, the genetic variability between the strains was examined from a representational sample of the population of each strain. Fastest growing strains grew to a set weight of 350 g more rapidly regardless of whether they were fed at a fixed rate or to apparent satiation. These faster growing strains also exhibited a lower FCR and higher SGR and TGC values, and higher percentage protein retention. The IHNV neutralization titers for the strains varied considerably with one high humoral response group and one low humoral response group. The remaining three strains clustered approximately midway between the other two. Genetically, the strains exhibited a pattern of wide divergence, with only 9 common alleles out of a total of 89 different alleles between the five strains. As expected, commercial aquaculture strains reared locally were genetically more similar, and strains that have undergone intense selection tended to have a strong correlation between reduced genetic variability, FCR, and SGR as compared to noncommercial strains.