Ontogenetic development of the digestive tract in Cuban gar (Atractosteus tristoechus) larvae

Abstract

Histological method was used to describe the development of the digestive tract in Atractosteus tristoechus larvae reared under culture conditions. The larvae were kept at 28 ± 1 C in three 15 L circular tanks for 18 days and they were fed with Artemia. According to the structural changes in the digestive system, three significant stages were established: (1) lecithotrophic, (2) lecithoexotrophic and (3) exotroph- ic. The first stage spanned from hatching to 3 days after hatching (DAH), the digestive system started to differentiate and larvae depended entirely on the endogenous nutrition from the yolk sac. During second stage (4-10 DAH), considered critical since it is the transition period to exotrophic feeding, the digestive tract was fully differentiated into buccopharynx, esophagus, non-glandular and glandu- lar stomach, anterior and posterior intestine. First periodic Schiff reagent-positive goblet cells also appeared, interdispersed within the epithelium of the digestive tract, increasing substantially in numbers and distribution as development continued. At this early stage, gastric glands were only observed in the fundic stomach and not in the cardiac and pyloric region. Pyloric caeca, spiral valve and rectum were also clearly distinguishable in the intestine. After the onset of the exogenous feeding (11-18 DAH), the organization and differentiation of the digestive tract did not undergo any noticeable modification, only the increase in size and complexity of the structures, and it attained the four tissue layer arrangement character- istic of adult vertebrates.