Histological and histochemical development of the digestive system of Solea senegalensis (Kaup, 1858) larvae

Abstract

The digestive system of Solea senegalensis was studied from hatching until 1 month of larval life. Histological and histochemical procedures were used to study the histomorphology, digestive enzymes, lipid, protein and carbohydrate distribution in the digestive larval tract. The major events in digestive system differentiation occurred during the early stages. At first feeding (2DAH—days after hatching) both the mouth and anus had opened and the digestive tract was differentiated in five portions: buccal–pharyngeal cavity, esophagus, incipient stomach, anterior and posterior intestine. The pancreas and liver were also differentiated at this stage. During metamorphosis (12 to 20DAH) an elongation of the digestive tract and increase in the absorption surface were observed. Gastric glands were observed around 27DAH. Alkaline and acid phosphatase, lipase and aminopeptidase activities were observed from the mouth opening onwards and increased with larval development. Proteins exhibited a similar pattern of increase being especially abundant in the intestinal epithelium and exocrine pancreas. Neutral lipids were abundant in the yolk sac (oil globule), intestinal epithelium and liver (hepatocytes). Esophageal mucous cells were rich in sulphated mucosubstances and intestinal mucous cells, intestinal epithelium and liver were rich in neutral mucosubstances. Glycogen deposition was observed after 7DAH in liver and intestinal epithelium. The analysis of data obtained in this study suggests that after 31DAH S. senegalensis larvae are capable of ingesting, digesting and absorbing nutrients, having a morphologically complete digestive tract, equipped with digestive enzymes.