Ontogeny of cholecystokinin-immunoreactive cells in the digestive tract of bluefin tuna, Thunnus thynnus, larvae

The appearance and distribution of cholecystokinin (CCK)-immunoreactive (IR) cells in the digestive tract of cultured developing larvae of bluefin tuna, Thunnus thynnus, were investigated by immunohistochemistry. The CCK-IR cells had an elongated triangular shape and a thin apex pointing towards the lumen of the gut. Very few weakly stained CCK-IR cells were found at hatching (0 days after hatching, DAH) and first feeding (3 DAH), while strongly stained CCK-IR cells were detected in all the larvae examined after 12 DAH. CCK-IR cells were scattered both in the pyloric caeca and the anterior intestine at 12 DAH, while the distribution was restricted to the pyloric caeca at 22 DAH. The relationships between the ontogeny of CCK and pancreatic enzymes are discussed.