Gastrointestinal evacuation and return of appetite in Atlantic halibut (Hippoglossus hippoglossus L.)

Grow-out Atlantic halibut ( Hippoglossus hippoglossus ) grows slowly, partly due to limited and varied feed intake. This study aimed to determine gastrointestinal (GIT) evacuation time and examine correlations between GIT filling, transit time, and mRNA expression of appetite-controlling genes. Six groups of 1, 2, and 3 kg individuals were fed a single meal with size-adjusted pellets and sampled 1, 3, 6, 10, 23, 48, 71, 96, and 120 h post-feeding. Appetite variation between individuals and groups was similar to industry observations. A logarithmic gastric evacuation model for 1 kg halibut fed 7 mm pellets predicted 50 % content evacuated at 8.6 h, 75 % at 25.2 h, and total evacuation at 73.9 h. Gastric lag phase lasted 1–3 h, with total gastrointestinal clearance estimated at 96–120 h . Expression of peptide yy paralogs in the anterior midgut positively correlated with midgut content, indicating a role in digestion/satiety signalling. Expression of ghrelin and cholecystokinin 1 levels remained unchanged in the stomach and anterior midgut. Hypothalamic mRNA levels of agouti-related peptide and neuropeptide y a increased 48 h post-feeding, correlating negatively with stomach content and suggesting orexigenic roles, while neuropeptide y b expression decreased post-feeding, indicating anorexigenic function. Despite rapid stomach evacuation (within 24 h), neuropeptide y a and agouti-related peptide expression increased only after 48 h, coinciding with 90 % gastric evacuation. This suggests appetite returns 48 h post-feeding, influenced more by midgut signals, potentially peptide yy paralogs, than by gastric filling. • Gastric evacuation model established for 1 kg halibut. • Weak correlation between gastric emptying and orexigenic gene expression. • Peptide yy mRNA expression correlates with intestinal compartment filling levels. • Orexigenic hypothalamic genes mRNA increased 48 h post-feeding. • Anorexigenic expression response for neuropeptide y b .