Department of Genetics

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Browsing Department of Genetics by Subject "Abalone culture -- South Africa"

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    The effect of triploidy on the growth and survival of the indigenous abalone, Haliotis midae, over a 24 month period under commercial rearing conditions
    (Stellenbosch : Stellenbosch University, 2008-03) Schoonbee, Lize; Brink, Danie; Stellenbosch University. Faculty of AgriSciences. Dept. of Genetics.
    ENGLISH ABSTRACT: Triploidy is the genetic state of containing three sets of chromosomes per cell in stead of two as in diploid organisms. The South African abalone (Haliotis midae) is naturally a diploid organism that sexually matures between four to eight years of age. Early sexual maturity is a disadvantage in cultured abalone stock, as the process of gonad development and spawning is energy demanding, causing energy to be diverted away from somatic growth. This same problem has been extensively experienced in diploid bivalve molluscs, where triploidy has since been applied as a means to prevent sexual maturation from occurring, thereby speeding up the growth process and shortening the time to marketing. Because triploidy was effective in bivalves, it was thought that it could contribute to faster growth in abalone as well. A procedure for the induction of triploidy in the abalone, Haliotis midae, was developed by De Beer (2004) and yielded up to 100 percent triploidy in treated abalone larvae. The next step was to compare the growth of the diploids and triploids to establish whether there was indeed a growth advantage on the part of the triploids, in view of commercial application. By using the same techniques as described by De Beer (2004), three groups consisting of triploid and diploid siblings were produced and subscribed to a comparative growth trial. The groups were spawned in three different seasons. The main objective was to establish whether there was in fact a difference in growth between diploid and triploid siblings, and whether seasonal effects were associated with growth advantages for either triploids or diploids. The two growth parameters measured were shell length and body weight. Measurements commenced at eight months of age, when the abalone could be individually tagged and continued up to the age of 24 months. The over-all results provided no convincing evidence of statistically significant faster growth of triploid juveniles compared to that of diploids up to two years of age. Growth differences were detected between seasons, but could not confidently be ascribed to seasonal environmental effects. The regression of shell length to body weight was similar for diploids and triploids.
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    Induction of triploidy in the South African abalone, Haliotis midae, by the use of hydrostatic pressure
    (Stellenbosch : University of Stellenbosch, 2004-12) De Beer, Mathilde; Brink, Danie; University of Stellenbosch. Faculty of Agrisciences. Dept. of Genetics.
    ENGLISH ABSTRACT: The indigenous abalone, Haliotis midae has been a successfully cultured aquaculture species in South Africa since 1990. It has a slow growth rate and takes from two to five years to reach market size. Like for most other commercially important abalone species, the slow growth rate of H. midae is a cause of concern with regard to the profitability of farming and global competitiveness of the species. Ploidy manipulation of the maternal genome, a universally growing practice in shellfish culture, is considered a promising method to improve the growth rate of abalone - a desirable trait in aquaculture organisms from a commercial perspective. This manipulation technique is employed to achieve sterility, which results in limited gonad development. The consequent re-allocation of resources to somatic growth results in improved growth. The purpose of this study was to establish a viable method for the induction and validation of triploidy, on a commercial scale, in the South African abalone, H. midae. The focus was on hydrostatic pressure as a method of induction and flow cytometry as the method of validation. The results obtained confirm hydrostatic pressure as an effective method for the induction of triploidy in H. midae, delivering high percentages of triploidy (>80%) over a wide range of pressures and times, in 48 hour-old larvae. Hydrostatic pressure had a negative effect on survival in 20 hour-old larvae. Flow cytometry was validated as a reliable, fast and accurate, though expensive, method for identification of triploidy in H. midae. As an outcome of this study a manual of “Procedures for the Induction and Validation of Triploidy in the abalone” is presented (Appendix 1) together with recommendations for further studies on triploidy in the South African abalone, H. midae.