| dc.description.abstract | Atlantic halibut, Hippoglossus hippoglossus, is a highly valued and well-established fish species that has gotten its reputation from being a high-end product from the fishery industry. Because of halibut overfishing and its fishery sustainability issues, the demand for a steady supply creates opportunities for aquaculture of halibut to succeed. In Norway, the halibut aquaculture industry has been active for the last couple of decades, and it aims to be a substantial niche in the Norwegian aquaculture industry. On its road towards success many challenges have been identified and, to some extent solved. However, today one of the major remaining problems is the fish’s lack of interest in commercial feed. Thus, farming of Atlantic halibut will be more efficient if the feed intake and feed efficiency is improved by optimizing the feed composition. In this thesis the appetite response and growth performance of grow-out halibut (317.7 ± 80.5 g) was studied when groups of fish were fed with 12 different feed compositions and varying macronutrient levels over a period of 60 weeks. Supporting previous findings, grow-out halibut grow better when given lower protein diets. Elevated dietary lipid (levels up until 25%) induced high growth, even though the apparent appetite was lower for these diets. However, increasing dietary lipid up to 30% resulted in major growth reduction. This supports previous findings for an upper tolerable limit for lipid content in formulated diets. Further, for carbohydrates, increased levels up to 25% of dietary inclusion was tolerated while maintaining the growth performance, contradicting previous findings. Furthermore, a correlation between appetite and elevated carbohydrate content was found, as well as with decreased dietary lipid. The results indicate that lower protein diets, down to 45% dietary inclusion, with higher lipid and carbohydrate contents can be used in the grow-out stages for halibut. Since feed protein usually is the highest cost feed ingredient, the results of this thesis can serve as a basis for the industry to produce more affordable diets for Atlantic halibut, enhancing its profitability. Also, the role of carbohydrates and lipid as appetite modulators in fish species is a research area that warrants further investigation in the formulation of an optimal feed that encourage feed intake. Thus, this thesis contributes to supplying further knowledge regarding ideal macronutrient gradients for enhancing appetite, growth, and fish welfare for the aquaculture of Atlantic halibut. | |
