Gonadal differentiation, hormonal sex reversal and triploidy in Arctic charr, Salvelinus alpinus

The purpose of this study was to develop and evaluate protocols for the production of monosex and sterile Arctic charr populations for the commercial aquaculture industry. The first goal was to determine the timing of gonadal differentiation, this being the most important factor for developing successful hormone administration methods to achieve sex reversal. To identify the timing of gonadal differentiation, random samples of 10 fish were collected weekly (every 55 to 90°C-days) from 194°C-days post-hatch until 1410°C-days post-hatch and prepared for histology. The timing of gonadal sex differentiation was determined to occur between 510--681°C-days post-hatch by comparing photomicrographs from the salmonid literature to the serial cross-sections of Arctic charr.;The third goal was to produce triploid Arctic charr and evaluate their survival and growth. The production of all-female triploid populations is more desirable than mixed-sex triploid populations for commercial aquaculture because female triploids are sterile. Fertilized eggs from 8 families of charr treated in a hydraulic pressure chamber at 9500 psi for 5 minutes at 210°C-min post-fertilization resulted in all-triploid populations with reduced survival relative to their diploid counterparts. The average survival rate for diploid and triploid families was 84% and 70%, respectively. A growth study using two 4m3 tanks containing 100 diploids and 100 triploids of each family showed that diploid fish consistently had larger average body weight and average fork length than their triploid counterparts at every sampling date when grown together under identical conditions.;The second goal was to use this knowledge for hormonal sex reversal of genotypic female fish using 17alpha-methyldihydrotestosterone (MDHT). The production of sex reversed males is necessary for creating an all-female population by indirect feminization. Two techniques, immersion and feeding treatments, were evaluated for effective hormonal sex reversal. The most effective treatment, daily feeding treatments of 0.5 mg/kg of MDHT for 600°C-days, resulted in a population composed of 90% phenotypic males.