Ontogeny of Cholecystokinin-Immunoreactive Cells in the Digestive Tract of Atlantic Halibut, Hippoglossus hippoglossus, Larvae

The appearance and distribution of cholecystokinin (CCK)-producing cells were investigated in the digestive tract of developing larvae of cultured Atlantic halibut, Hippoglossus hippoglossus. The CCK-producing cells were detected immunohistochemically, by use of a primary antiserum against CCK cloned for the Japanese flounder, Paralichthys olivaceus. No CCK-immunoreactive (IR) cells were detected in first-feeding larvae (33 days after hatching, DAH). Forty-five DAH or 12 days after first feeding, there were a few scattered CCK-IR cells in the epithelium of the anterior midgut in about 30% of the examined larvae. All larvae older than 52 DAH had CCK-IR cells in the anterior midgut, particularly frequent in the most anterior region adjacent to the pyloric caeca. No CCK-IR cells were detected in the foregut, the hindgut, or the midgut posterior to the first curvature. The CCK-IR cells spanned the intestinal epithelium from the basal lamina to the lumen and were triangular in shape, with the nucleus in the basal part and a thin apex toward the lumen. The mechanisms controlling release of bile, pancreatic enzymes, and peristalsis during the 12 days between first feeding and the first detection of CCK-IR cells remain to be clarified.