Ontogeny of the digestive tract in stinging catfish, Heteropneustes fossilis (Bloch) larvae.

Abstract

Heteropneustes fossilis (Bloch) is an important candidate species for diversification of freshwater aquaculture in India. However, high mortality rate during larval rearing is the most serious bottleneck in commercial production of this species. A proper understanding of the ontogenic development of digestive system provides the basis to understand the nutritional physiology of larvae and develop appropriate feeding strategies. In the present study, the ontogenical development of the digestive tract in H. fossilis larvae was studied from hatching until 30day post-hatching (dph) at 29°C. At hatching (2.8 ± 0.2mm standard length, SL), the digestive tract was undifferentiated and attached dorsally to the yolk sac. At 1dph (2.9 ± 0.2mm SL), the mouth opened and oral valves were visible. At 2dph (3.0 ± 0.3mm SL), goblet cells were observed in the buccoparyngaeal cavity. At this age, exogenous feeding started and the intestine was differentiated into the anterior and posterior regions, and the rudimentary liver and pancreas were also seen. Small supranuclear vacuoles were observed in the enterocytes of the posterior intestine at 2dph. Zymogen granules were observed in acinar cells of pancreas by 3dph, and islets of Langerhans were visible at 4dph (3.5 ± 0.1mm SL). At the same age, most of the yolk sac reserves were consumed, whereas they were completely exhausted by 5dph (3.9 ± 0.5mm SL). Between 4 and 6dph, the liver elongated in size and started to accumulate lipids in the hepatocytes. Gastric glands were detected at 4dph, and the pyloric sphincter was completely differentiated at 9dph (6.1 ± 0.4mm SL) as an epithelial fold that separated stomach from the anterior intestine. By 13dph (8.6 ± 0.2mm SL), profuse gastric glands were visible inside longitudinal mucosal folds of the stomach. The formation of gastric glands and their development were noticed as the last events in the development of the digestive tract in H. fossilis. This indicated the end of the larval period and the commencement of the juvenile stage. Considering these observations, it is suggested that H. fossilis larvae have a morphologically complete digestive tract by 13dph. The findings of the study on the development of the digestive system in H. fossilis may help in synchronising the larval stage of development and feeding strategies and would be helpful in improving larval rearing techniques for catfish species.