Histological study of the organogenesis of the digestive system and swim bladder of the Dover sole, Solea solea (Linnaeus 1758)

The search for histological criteria related to starvation of Dover sole larvae necessitated a preliminary description of the digestive tract, its associated glands and the swim bladder morphogenesis from hatching to day 30. After hatching, the digestive tract is a simple undifferentiated tube, closed anteriorly. The larval period begins with the opening of the mouth. The digestive tract then becomes functional with differentiation of the oesophagus (which begins to secrete abundant mucus), the future stomach and the convoluted gut. The liver, gall bladder and pancreas also become apparent at this time. The first signs of intestinal absorption appear quickly after first feeding and can be identified as vacuoles in the midgut and eosinophilic granules in the hindgut. Glycogen is then progressively stored in the liver. This is followed by the formation of muscle layers, tooth development and swim bladder inflation. After metamorphosis, the appearance of the gastric glands indicates a change in digestion and the passage through the juvenile period.