MORPHOGENESIS OF THE DIGESTIVE-SYSTEM AND SWIM BLADDER OF THE TURBOT, SCOPHTHALMUS-MAXIMUS L AQUACULTURE

The study is based on serial sections made on turbots raised at 18 .+-. 0.5.degree. C from day 1 (post-hatching) to day 20. Histological changes of the digestive system and swim bladder were observed on a daily basis. At day 1, specimens (total length, Lt = 3.0-3.1 mm) present a digestive tract undifferentiated along its length and closed anteriorly. They belong to the embryonic period in spite of the presence of associated digestive glands (liver and pancreas). The larval period extends from day 2 to day 14-15 (Lt = 3.5-7.0 mm): the swim bladder differentiates and inflates, then the pneumatic duct binding the swim bladder to the stomach degenerates; regional differences appear along the digestive tract which starts to be functional. From day 15-16 (Lt = 6.9-7.7 mm) the juvenile period begins with the formation of gastric glands and the onset of gastric digestion. Two pyloric caeca are clearly visible and the number of intestinal folds and goblet cells increases progressively.