Historically, t he two most expensive components of salmonid aquaculture feeds have been fish meal and fish oil as the primary protein and lipid sources. As the feed industry moves toward the use of less expensive, alternative protein and lipid sources, the fatty acid profile of feeds can change significantly. Rainbow trout (Onchorynchus mykiss) are capable of fatty acid sensing and juveniles have been suggested to differentiate diets and consume more feed in the presence of docosahexaenoic acid (DHA ) and Eicosapentaenoic acid (EPA) . However, much remains unknown regarding the mechanisms behind feed consumption. The objective of this project was to better understand the effects of fatty acid signaling postprandially relative to feed consumption. This knowledge will be crucial toward maximizing the sustainability of aquaculture feeds by more effectively balancing lipid sources to increase fatty acids that stimulate feed intake, while reducing those that suppress feed intake.
The effects on feed consumption of six individual, purified fatty acids were observed. Oleic acid (OA), palmitic acid (PA), alpha-linolenic acid (ALA), linoleic acid (LA), EPA, and DHA were each individually gavaged into juvenile rainbow trout; a sham treatment for each fatty acid was also administered. After fish were gavaged, 30 minutes was allotted for fish to recover and generate a response to the treatment or sham. Then all fish were fed to satiation and sampled at 30 minutes and 60 minutes postprandial . At both timepoints, t he hypothalamus was collected to measure gene expression of two anorexigenic neuropeptides, pro-opio melanocortin (POMC) and cocaine-and-amphetamine-related transcript (CART) ; as well as two orexigenic neuropeptides, neuropeptide Y (NPY) and agouti-related peptide (AgRP). Feed consumption for each treatment was also measured for correlation of feed consumption to gene expression.
Trends in preliminary data suggest decreased feed consumption relative to sham controls for PA, EPA, and DHA. When comparing across fatty acids, pairwise comparison showed PA treatment reduced feed intake relative to other treatments with the exception of DHA (P<0.05) , and DHA treated fish consumed less feed than EPA treated fish (P<0.05). Therefore, early results suggest that individual fatty acids have the capacity to influence feed intake postprandially in rainbow trout. The impacts of these fatty acids on genes encoding hypothalamic regulators of appetite will also be discussed.