Masters Degrees (Genetics)

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Browsing Masters Degrees (Genetics) by Subject "Abalone canning"

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    Quantitative assessment of yield traits between family groups of the cultured abalone, Haliotis midae, during the process of canning
    (Stellenbosch : Stellenbosch University, 2013-03) Gerber, Maria Elizabeth (Mariette); Brink, Danie; Stellenbosch University. Faculty of AgriSciences. Dept. of Genetics.
    ENGLISH ABSTRACT: The species Haliotis midae is of great commercial value to the South African abalone industry and is mainly exported to Asian markets, specifically China. Up to 50% is sold as canned products with H. midae registering an average canning yield of approximately 35%. The species is presently genetically undomesticated and breeding programmes are being introduced to improve a range of production traits of which growth and yield is of primary importance. The objective of the study was to determine genetic parameters such as heritability, genotypic and phenotypic correlations of yield-related traits to assess the potential genetic improvement through selective breeding. A series of yield-related parameters were identified that is of relevance to the standard abalone canning procedure. Low to moderate heritabilities where recorded for most traits, including pre-shuck/live weight (0.20 ± 0.06), post-shuck weight (0.15 ± 0.05), post-gut weight (0.15 ± 0.05), post-brine weight (0.19 ± 0.06), pre-canning weight (0.19 ± 0.06), post-canning weight (0.21 ± 0.06), shell weight (0.16 ± 0.05), canning yield percentage (0.08 ± 0.03) and shell weight to post-gut weight ratio (SW: PGW) (0.09 ± 0.04). Weight related parameters are phenotypically highly correlated (0.86 ≤ r ≤ 0.99) but show negative correlation with canning yield percentage (-0.38 ≤ r ≤ 0.04). The nett yield of abalone shows a relatively strong positive correlation with the live weight (r = 0.66). Shell length is highly heritable (h2 ≈ 0.48) and show a strong positive correlation with live weight (r = 0.94). Shell weight is also highly correlated with live weight (r = 0.80) and the SW: PGW ratio does not show a significant correlate with live weight (r = 0.03). Weight-related traits show heritability values ranging from 0.15 to 0.20 that could allow a positive genetic response. Shell length (as a linear growth parameter) shows a high heritability (h2 ≈ 0.48) and a strong positive correlation with live weight (r = 0.94) which also makes it suitable for use as a selection criterion in breeding programmes for improved growth rate. Direct selection for canning yield is compromised by the destructive nature of measurement and the low heritability (h2 < 0.10). The negative correlations between yield as a percentage and growth traits (-0.38 ≤ r ≤ 0.04) further complicate its use as a direct breeding objective. Although the canning yield as a percentage shows a decrease with an increase in live weight, the nett canning yield increases (r = 0.66) with the live weight. It is therefore recommended to use shell length as a criterion for selection for increased growth rate and nett yield, thereby optimising profitability.