Histological and histochemical study of the digestive system of the Argentine anchovy larvae (Engraulis anchoita) at different developmental stages of their ontogenetic development

Abstract

In this work, histological and histochemical features of the larval digestive system of Argentine anchovy Engraulis anchoita were described. Structural changes during ontogenetic development were also characterized, and comparisons between the beginning and the end of larval development were made. Histological sections of larvae were subjected to histochemical and routine histological techniques to localize and differentiate glycoproteins (GPs). Both at an early and a late larval stage, the oesophageal goblet cells reacted more intensely than those of the rest of the digestive tract, and only the oesophagus exhibited metachromasia with toluidine blue techniques at different pHs, thus revealing diverse GPs at different concentrations. The GPs histochemical composition in the intestine varied with the developmental stage and the intestinal zone. The absence of goblet cells characterized the foregut; however, they started differentiation at an advanced stage in the midgut. These cells could be detected in the hindgut both at the beginning and at the end of development. The attached glands showed a varied glycoprotein composition. The digestive tract of E. anchoita presented a high level of complexity, related to the multiple functions of mucus in the digestive tract, such as lubrication, protection, antimicrobial function and ionic and osmotic regulation.