Browsing by Author "Vlok, Arnoldus Christiaan"

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    Genetic assessment of five breeding populations of abalone (Haliotis midae) through a comparative Performance Testing Scheme
    (Stellenbosch : Stellenbosch University, 2015-04) Vlok, Arnoldus Christiaan; Brink, Danie; Stellenbosch University. Faculty of Agrisciences. Dept. of Genetics.
    ENGLISH ABSTRACT: Cultured abalone in South Africa is undomesticated. For the local industry to remain competitive on the international markets it is essential to improve production. This study is part of a selective breeding component of a larger genetic programme that aims to enhance productivity of the local industry by genetic improvement of growth rates. Selective breeding programmes are based on genetic variation and correlations. Molecular studies proved genetic differentiation exist between the broodstock- and offspring populations and among the offspring populations used in this study. Five commercial abalone farms from the Walker bay region each entered 3000 randomly selected animals obtained from synchronised mass spawning of conditioned broodstock into a Performance Recording Scheme (PRS). Microsatellite marker analysis proved these broodstock populations to be representative of the wild populations. The five cohorts were assessed over the five locations represented by three replicates per location with 200 randomly assigned animals per replicate. The average growth rate was used as growth performance parameter by measuring shell length and body weight at three month intervals over a period of 24 months. Interaction was observed between cohort and location effects when analysing the full data set. This was unexpected as the cohorts were constructed from parent stick that was randomly sampled from the same geographical area, the larger Walker bay. The factors suspected of causing this observed interaction were considered in a stepwise analysis. Initial and progressive tag loss, differences in initial size of animals entered into the study and on-farm management errors were considered as possible causes of the observed interaction in a stepwise analysis. Statistically significant differences were observed between the five cohorts and between the five locations in terms of length and weight growth rates. Based on these findings it is advised that a central facility is used to effectively compare the growth rates of different cohorts or populations. Any future research in selective breeding to follow this study should involve the integration of molecular techniques and biotechnologies.