Genetic improvement of growth rate in rainbow trout (Oncorhynchus mykiss)

[摘要] ENGLISH ABSTRACT: A breeding programme aimed at the genetic improvement of growth rate of rainbow trout was initiated in1988 by the Department of Genetics, University of Stellenbosch, in collaboration with the local troutproducer's organisations. The first phase of the breeding programme included the collection, evaluation andselection of the best available genetic material from 13 different genetic groups (nine local and fouroverseas) to make up two separate base populations as odd and even year-groups. This was done toestablishment a base population with high genetic merit and variation at the onset of the breedingprogramme. Statistically significant and commercially valuable genetic differences in terms of weight andlength gain were detected between the various hatchery groups.The next two generations of the breeding program included a series of single and double crosses in order toincrease the levels of genetic variation in the base populations, and to investigate possible heterosis andspecific and general combining ability among the crosses. Significant levels of heterosis (6.7% to 9.6%) andgeneral combining ability was found for weight and length gain during consecutive growth stages. Noevidence was found for specific combining ability among the crosses. The crossing of selected offspringfrom the original genetic groups followed by the application of intensive multi-stage selection for growthrate within progeny groups has led to the establishment of second and third generation parental populationswith higher levels of genetic variation and improved individual genetic merit with regard to growth rate. Theexploitation of non-additive genetic variation within the base populations through crossbreeding andheterosis during the early stages of the selection programme was delayed in favour of the utilization ofadditive genetic variance through a procedure of multi-stage selection that incorporated high intensities ofselection within and between family groups.The estimation of genetic parameters during the fourth generation on the basis of a hierarchical half-sibfamily structure confirmed the presence of high levels of additive genetic variation within the respectivepopulations/year-groups. High heritability values in the range of 0.40 to 0.53 were recorded for body weightand length at 150 days. Genetic correlations between the traits were also high, in the range of 0.74 to 0.82.The cumulative realized response of 50% in body length for the EVEN year-group after six generations ofselection (8.3% per generation), and the 33% for the ODD year-group after five generations of selection(6.6% per generation) confirms the efficiency of the multi-stage selection procedure to exploit the availableadditive genetic variation for growth rate within the respective populations.The programme is still ongoing, entering its 7th generation in 2004 and is supplying about 50-60% ofcommercial material through direct supplies of broodstock, ova and fingerlings and indirect supplies viamultiplier stations (commercial hatcheries). The programme was the first of its kind in relation toaquaculture species in the Southern African region, and has since initiated the introduction of programmes ofgenetic improvement in three other indigenous species, namely tilapia (Oreochromis mossambicus), Africancatfish (Clarias gariepinus) and abalone (Haliotis midae).

[发布机构] Stellenbosch University