Effect of strain and diet on growth and proximate composition of triploid salmonids

The use of sterile triploids in aquaculture would potentially allow fish to have continued growth for larger market size and controllable harvest times throughout the year. However, the effects of triploidy on fish growth are unpredictable, likely due to factors such as life stage at evaluation, genetics and husbandry conditions. Comprehensive reviews of the biology and culture characteristics of triploid fish indicate a lack of research on their nutritional requirements, yet this baseline information on nutritional status is essential for optimizing fish performance. The aims of this thesis were therefore to (a) investigate the body composition and growth of triploid Atlantic salmon from freshwater juvenile (parr) stage to harvest in a commercial aquaculture setting, (b) determine whether a difference in energy requirement could be the cause for reduced triploid performance and (c) examine the effects of strain and ploidy on the growth of Atlantic salmon post-smolts in a 12-week tank trial, using plasma insulin-like growth factor I (IGF-I), condition factor (CF) and specific growth rate (SGR) as indicators of growth.;There was no difference in growth rate of triploids and diploids in the commercial trial in terms of weight gain, although triploids were longer and had a lower condition factor. With the exception of the smolt stage just prior to seawater transfer, triploids had lower energy, lipid, dry matter and protein levels than diploids, although not statistically significant. Triploids appeared to be most affected during winter, suggesting that they may require modified diets formulated to provide additional nutrients to cope with winter stress. iii.;In the dietary energy requirement study, triploids had lower growth rates and condition factor on all three experimental diets compared to diploids but there was no effect of ploidy on food conversion efficiency. Triploids had lower whole-body lipid content but equal protein content, which resulted in lower energy content compared to diploids at both the initial and final samplings. There was no effect of diet or ploidy on plasma IGF-I concentrations. Triploidy did not affect feed digestibility, suggesting that the reduced performance of triploids must be due to a difference in metabolic energy utilization.;In the final study, significant variation was found between strains for triploid growth. In addition, a wild strain outperformed domesticated strains as diploids. These results provide important information to salmon farmers on the successful use of triploids and the continued need for broodstock development.;This thesis has shown that IGF-I, which is instrumental in growth, did not differ in circulating levels between ploidies, and that triploids did not differ from diploids in their food conversion efficiency and apparent digestibility. Based on these results, energy available to triploids should be equal to diploids. Nevertheless, triploids had lower growth rates and whole body energy and lipid composition. Future research should investigate the effect of triploidy on metabolic energy utilization so that diet formulations can be modified to meet their energy requirements.