Growth performance comparison of intercross-triploid, induced triploid, and diploid rainbow trout

Authors: Weber, Gregory - Greg; Hostuttler, Mark; Cleveland, Beth; Leeds, Timothy - Tim

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/5/2014
Publication Date: 6/5/2014
Publication URL: http://handle.nal.usda.gov/10113/58960
Citation: Weber, G.M., Hostuttler, M.A., Cleveland, B.M., Leeds, T.D. 2014. Growth performance comparison of intercross-triploid, induced triploid, and diploid rainbow trout. Aquaculture. 433:85-93.

Interpretive Summary: The rainbow trout industry is interested in raising fish that are sterile and do not grow gonads in order to prevent escaped farmed fish from displacing or breeding with native species and because they have superior fillet quality, growth, and feed conversion at normal reproductive sizes. Currently, rainbow trout are sterilized by triploidization which is a process where the fish are induced to have three sets of chromosomes (triploid) instead of the normal two sets of chromosomes (diploid). Although both sexes of these triploid animals are sterile, the males still grow large testes whereas the females do not grow ovaries. For this reason triploids raised as foodfish are all-female lines. Triploid fish are commonly produced by pressure or temperature shock of the newly fertilized egg (induced-triploid, 3NP). The problem with this approach is that you have to treat every egg to make it a triploid, and since the process is not 100% effective, you have to test every batch of eggs to determine if the procedure was successful. In addition, this procedure can cause deformities. We have been working on improving an alternative method for making triploids which in theory should result in 100% sterile offspring. This entails mating a parent that has four sets of chromosomes, a tetraploid (4N), with a diploid (2N) parent (intercross-triploid, 3NC). In the current study we compared growth performance of nine sets of genetically-related 2N, 3NP and 3NC families. All of the fish expected to be triploid were confirmed to be triploid. The 3NC fish grew faster and larger than the 3NP fish, and had a lower rate of deformity supporting this alternative method of making triploids results in a better fish for production. The 3NC fish grew at similar rates as the normal 2N fish until the normal 2N which are fertile, started to slow in growth as they began to grow ovaries. At the end of the study the 3NC fish were 28% heavier than the 2N or 3NP fish and the 3NC fish also had similar rates of deformity as the 2N fish. The 3NC fish were also slimmer than the 2N and 3NP fish which some consider a more appealing look, but may reduce fillet yields. In all, the performance of the 3NC fish was superior to that of the 3NP and 2N fish supporting consideration of 3NC fish for production of fish that are raised to or beyond reproductive age or pose a potential risk from escapement.

Technical Abstract: All-female triploid fish are advantageous in rainbow trout (Oncorhynchus mykiss) aquaculture due to sterility and the consequent superior fillet quality, growth, and feed conversion achieved at reproductive size. Triploid fish are commonly produced by pressure or temperature shock of the zygote (induced-triploid, 3NP), but can also be produced by mating a tetraploid parent with a diploid (2N) parent (intercross-triploid, 3NC). We compared growth performance of nine sets of families each consisting of 2N, 3NP and 3NC siblings from fry through two years of age. The 2N and 3NC fish exhibited greater body weight than the 3NP fish throughout most of the study. The 3NC fish were heavier than the 2N fish during year one although this advantage disappeared during most of year two, until 2N growth slowed during gonadal maturation. The specific growth rate of the 3NP fish also exceeded that of the 2N fish late in sexual maturation resulting in similar body weights near spawning. The 3NC fish exhibited the lowest and 3NP the highest condition factor throughout most of the study. The correlations of body weight among families for the three ploidy types ranged from R2 below 0.03 around 8-9 months post-hatch, to above 0.5 around the middle of year two, supporting family differences in growth in response to triploidization and triploidization strategy. The 2N values were more highly correlated to 3NC than 3NP values. The 3NP fish had higher rates of vertebral compression than the other ploidy groups which affected body weight, fork length, condition factor and feed intake.