Animal and Aquacultural Sciences
Carlos Lozano defended his PhD thesis on December 15th 2011
Ane Gro Siri Skjelfjord
A quantitative genetic study on the proportion of males in Tilapia
Summary from the thesis - PhD thesis 2011:63
Author: Carlos Lozano
Early sexual maturation is one of the main constraints in Tilapia farming since early breeding causes stunted growth and large size variability. To circumvent this problem all-male populations are used commercially, and production of all male fry with use of hormones is the industry standard for Nile tilapia. To evaluate alternatives for production of all male fry, variation of male proportion of different strains and among strains combinations of Nile tilapia were studied. Additionally, to evaluate the feasibility of selection for increased male proportion, genetic parameters for male proportion were studied in Nile tilapia and hybrids between Nile and blue tilapias.
None of the eight purebred Nile tilapia strain and strain crosses evaluated in Paper I
showed a male proportion (MP) close to the desired commercial threshold (above 95% males). Additive genetic variation for male proportion was estimated within a synthetic population of Nile tilapia. Moderate to low heritabilities were obtained, but estimates may be biased upwards due to effects of the major genetic sex determination factors. Selection for increased male proportion will be very difficult to implement since it likely will result in an increased proportion of masculinized XX sires, which will counteract the response to selection. If selection is to be implemented, use of hormones will be needed to reproduce the population. Identification of genetic sex through the use of genetic markers could provide more reliable estimates of the genetic parameters for MP.
Genetic variation was also estimated among hybrids of Nile tilapia females and blue tilapia males. Heritability estimates were moderate to high. Since only one generation of data was evaluated there can still be some level of confounding between the additive genetic effects and the other effects common to full-sibs due to shallow pedigrees. Crossbreeding (hybrid production) may be a good way to increase male proportion in places where cold winters affect production since hybrids between these two species show high male proportion and increased low temperature tolerance as compared to pure Nile tilapia. To make the Nile x blue tilapia hybrid of interest also in a tropical environment the growth of the blue tilapia must be improved through selection.
Updated: 27.12.11Printerfriendly version
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