Development of the digestive system in dusky kob,Argyrosomus japonicus,larvae

In order to contribute to the development of larval rearing technologies of dusky kob, Argyrosomus japonicus, we studied the morphology and histology of the larval digestive system from hatching to 30 days after hatch. At hatch, the digestive tract appeared as a simple tube. The mouth was closed (endogenous feeding) and it opened by 65 degree days (DD). Supranuclear vacuoles appeared by 88 DD, initiating exogenous feeding. By 145 DD, the oil globule had disappeared. The stomach, intestine, rectum and gastric glands were visible by 224 DD. Number and size of supranuclear vacuoles began to decrease with progressive vacuolisation of the enterocytes and intestinal folds became obvious. The rectum was well differentiated at 338 DD but lacked supranuclear vacuoles in the enterocytes, suggesting limited nutrient absorption. At this stage, lipid absorption shifted to the hindgut, which now contained many lipid vacuoles. Goblet cells were visible in the midgut as gastric glands appeared, and their number increased from 292 DD. At the start of the third developmental phase, the larvae had a fully functional digestive system.