The main aim of this study is to increase the male to female ratio through the application of a suitable level of temperature during a given number of days in the Genetically Improved Farmed Tilapia (GIFT) strain. The parental fish used in this experiment came from the 6th generation of selection for increased body weight at harvest in the GIFT strain in Malaysia. In 2008, 25 full- and half-sibs families (from 21 sires and 25 dams) were produced over two batches with a total of 18035 fry, averaging 724 fry per family. Soon after egg yolk absorption, the newly hatched fry of each family were split into three groups of equal size. One group was reared under normal water temperature between 28 and 30 oC (control). The temperature treatments were applied to other groups for which water temperature was set at 36oC and 38oC and kept constant by special heaters for 10 and 5 days, respectively. After the treatment period, the fry of each family were returned to normal water conditions in separate hapas installed in tanks. All groups were subject to the same feeding and management regimes throughout the experimental period. A total of 1,760 fingerlings of an average size of 5 g were sexed using the aceto-carmine staining method. At sexing, measurements of body weight and standard length were recorded on individual fish. The number of fish which survived after the treatment was also recorded. The data were analyzed using the SAS package. The results showed that the treatment groups had significantly lower survival rates than the control. The difference may have been due to experimental treatments, but factors such as tank effect, handling and others may have also influenced the results and their effect cannot be easily separated in the analysis. The percentage of males is given in Figure 1. It was greater than 50 in all cases, ranging from 67 to 72%. A Chi-square test, however, showed that there were no statistical differences between the experimental groups. Figure 2 presents the body weights of the experimental groups at sexing. The differences in body weight between the control and treatment groups were not statistically significant (P=0.08). Despite the limited success of the work conducted to date, we are conducting further trials aimed at producing all male progeny through a clean and environmentally friendly technology.
Relation
Asian-Pacific Aquaculture 2009, Kuala Lumpur, Malaysia 3-6 November 2009
135 Visitors
1 Downloads
Disclaimer |
Privacy |
