Feed residuals in the midgut supresses appetite in Atlantic halibut (Hippoglossus hippoglossus L.)

Abstract

Feed intake in gastric fish is constrained by stomach capacity, whereas appetite modulates meal timing and magnitude. Gastric evacuation usually has a strong impact on the return of appetite; however this linkage is weak in Atlantic halibut (Hippoglossus hippoglossus). In this study, we evaluated the effects of three feeding regimes—satiation meals offered daily, every second day, or every third day—on feed intake, growth, and appetite-related signalling peptides in the gut–brain axis of 2 kg Atlantic halibut. Growth rate and cumulative feed intake did not differ among treatments, although fish fed daily reduced feeding activity during meals. Pre-prandial examination of gastrointestinal contents showed that halibut fed more frequently than at 3-day intervals reduced meal size. This reduction correlated with higher expression of anorexigenic signals from the pyloric caeca cck1 and mid-intestinal pyy paralogs, triggered by residual digesta in these compartments. Further, agrp correlated negatively with elevated cck1 and pyy paralogs, supporting an inhibitory (satiation) stimulus on feed intake from the midgut. Hypothalamic cart2b, cart3b, and cck1 emerged as candidate anorexigenic biomarkers. These results demonstrate that grow-out halibut can be fed every second/third day without compromising performance. Less-frequent meals simplify behavioural monitoring, improve water quality by reducing uneaten feed, and lower operational costs and environmental impact.