Abstract
The demand for seafood, fueled by population growth, has heightened the need for sustainable seafood production. Aquaculture has emerged as a vital resource to alleviate the pressure on marine resources driven by the capture fisheries industry. However, fish oil sourced from ocean resources, has been a foundational ingredient in the diets of carnivorous fish such as rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar). Fish oil provides a rich source of omega-3 (n-3) long-chain polyunsaturated fatty acids (LC-PUFAs) which benefit fish health, as well as consumer health, and is considered a necessary ingredient for salmonids by fish nutritionists. Even so, fish oil inclusion has been drastically reduced as the aquaculture industry has matured. As aquafeeds continue to advance in sustainability, nutrient profiles of feed will drastically change. This thesis investigates the role of fatty acids associated with alternative oil sources in regulating feeding behavior and appetite in salmonids, by utilizing rainbow trout and Atlantic salmon. The first aim was to identify an inert carrier for delivery of free fatty acids (FFAs) to the gastrointestinal tract to study the roles they play in modulating the expression of appetite regulating neuropeptides, agouti-related peptide (AgRP), neuropeptide Y (NPY), pro-opiomelanocortin (POMC), and cocaine-and amphetamine-regulated transcript (CART). Three carriers were designed; of which, the most successful was a thin potato starch paper folded to hold a loose powder consisting of cellulose and cholesterol as the FFA carrier. Using this method, gene expression of AgRP, NPY, POMC, and CART was highly variable, limiting the ability to detect significant results (P < 0.05). Feed intake was also recorded following treatment; however, post-prandial results showed no difference in feed consumption following FFA treatment with the developed carrier. Learning from the complications observed in the first study, a second study was conducted. In this study, we focused on the effects that alternative oil sources may have on the same appetite regulating neuropeptides. Fish oil (FO), flax oil (FX), Nuseed Aquaterra® omega-3 canola oil (NU), and soy oil (SO) were used as treatments in this experiment in which the oil sources were orally gavaged into rainbow trout and Atlantic salmon. Overall, in rainbow trout, FX treatments demonstrated the strongest orexigenic response by upregulating NPY (P < 0.1) and AgRP (P < 0.05), as well as downregulating CART (P < 0.05), while the FO treatment had the strongest anorexigenic response with CART upregulated while NPY was downregulated (P < 0.05). InAtlantic salmon, the opposite effect was observed with the FX treatment having the strongest anorexigenic response, as demonstrated by the concurrent upregulation of POMC and downregulation of AgRP (P < 0.05). These results, observed in both research chapters, underscore the nuanced role of fatty acids in feed intake regulation and point towards future research directions for optimizing aquafeed formulations. While many challenges were presented in the current research, potential solutions to these challenges are addressed in the final chapter. This work contributes to the advancement of sustainable aquaculture practices by enhancing our understanding of dietary mechanisms influencing salmonid physiology and behavior.