Histomorphological changes in digestive tract of golden mahseer (Tor putitora) during different developmental stages

Histomorphological changes in digestive tract of golden mahseer (Tor putitora) were examined in larvae [starting from hatching to 45 days post-hatching (dph)], fry, fingerling, and adult. Digestive tract appeared during hatching, on the dorsal side of yolk sac, as a straight tube with a narrow lumen. Mouth opening and appearance of liver and pancreas were observed at 2 dph, and subsequently anal opening, appearance of goblet cells in esophagus, and posterior intestine were evident at 3 dph. The remodeling of oral cavity in terms of epithelial stratification, appearance of taste buds, and goblet cells were observed in a window of 4-5 dph. Intestinal folding was found to be initiated at 8 dph. From 12 to 45 dph, thickening of oral and esophageal mucosal/extramucosal layers, increase in intestinal folding, increases in the density of goblet cells in entire gut were observed. Within the same time window, other histological changes such as disappearance of vacuoles in liver, and abundance of zymogen granules in pancreas were also observed. Supranuclear vesicles in mid-to-posterior intestine were found to be prominent from first feeding to 45 dph; however, this phenomenon was no longer evident in fry and fingerling. Overall, the increase in intestinal folding and complexity of extramucosal layer were found to be continuous from the first appearance to adult, and this inferred the fact that the nutritional physiology, in terms of digestion and assimilation, progressively changes throughout the life stages of golden mahseer. Findings of this study will, therefore, help in preparing diets for different life stages of this fish, and in addition, the present information widens the understanding of digestive physiology of golden mahseer.