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

Abstract

Heteropneustes fossilis (Bloch) is an impor-tant candidate species for diversification of freshwateraquaculture in India. However, high mortality rate dur-ing larval rearing is the most serious bottleneck in com-mercial production of this species. A proper understand-ing of the ontogenic development of digestive systemprovides the basis to understand the nutritional physiol-ogy of larvae and develop appropriate feeding strategies.In the present study, the ontogenical development of thedigestive tract in H. fossilis larvae was studied fromhatching until 30 day post-hatching (dph) at 29 °C. Athatching (2.8± 0.2 mm standard length, SL), the diges-tive tract was undifferentiated and attached dorsally tothe yolk sac. At 1 dph (2.9 ± 0.2 mm SL), the mouthopened and oral valves were visible. At 2 dph (3.0 ±0.3 mm SL), goblet cells were observed in thebuccoparyngaeal cavity. At this age, exogenous feedingstarted and the intestine was differentiated into the an-terior and posterior regions, and the rudimentary liverand pancreas were also seen. Small supranuclear vacu-oles were observed in the enterocytes of the posteriorintestine at 2 dph. Zymogen granules were observed inacinar cells of pancreas by 3 dph, and islets ofLangerhans were visible at 4 dph (3.5 ±0.1 mm SL).At the same age, most of the yolk sac reserves wereconsumed, whereas they were completely exhausted by5 dph (3.9 ± 0.5 mm SL). Between 4 and 6 dph, the liverelongated in size and started to accumulate lipids in thehepatocytes. Gastric glands were detected at 4 dph, andthe pyloric sphincter was completely differentiated at9 dph (6.1 ± 0.4 mm SL) as an epithelial fold thatseparated stomach from the anterior intestine. By13 dph (8.6± 0.2 mm SL), profuse gastric glands werevisible inside longitudinal mucosal folds of the stomach.The formation of gastric glands and their developmentwere noticed as the last events in the development of thedigestive tract in H. fossilis. This indicated the end of thelarval period and the commencement of the juvenilestage. Considering these observations, it is suggestedthat H. fossilis larvae have a morphologically completedigestive tract by 13 dph. The findings of the study onthe development of the digestive system in H. fossilismay help in synchronising the larval stage of develop-ment and feeding strategies and would be helpful inimproving larval rearing techniques for catfish species.