Changes in the histology and digestive enzyme activity during digestive system development of silver pomfret (Pampus argenteus)

Abstract

Silver pomfret (Pampus argenteus) is an economically important marine fish species in the Indian and Western Pacific oceans, it has great aquaculture potential. Research on the ontogeny of the digestive system is critical in improving the larval rearing protocols and weaning process. In this study, an approach that integrates histology and biochemistry was used to illustrate the digestive system ontogeny of silver pomfret from hatching to 50 days post-hatching (dph). At 1 dph, the digestive system was differentiated into the esophageal sac, esophagus, anterior and posterior intestine, liver, pancreas, and gall bladder, and except for pepsin, digestive enzymes were detected. At 4 dph (4.0 ± 0.2 mm in total length, TL), the mouth opened to allow for exogenous feeding, which coincided with the development of papillae and mucous cells in the esophageal sac, indicating their preliminary function of grinding food. At 7 dph (4.5 ± 0.2 mm, TL), the larvae entered an exclusively exogenous feeding stage and numerous supranuclear vacuoles appeared in the posterior intestine. From 1 to 10 dph, alkaline phosphatase increased sharply, suggesting the rapid development of enterocytes and intestine. At 10 dph (4.8 ± 0.6 mm, TL), gastric glands appeared in the stomach, and from 14 to 20 dph (5.2 ± 0.3 to 6.1 ± 0.4 mm, TL), they multiplied greatly. At this time, the other digestive organs, including the esophageal sac, pyloric caeca, intestine, and accessory glands were well developed and tended to mature in structure. From 15 to 20 dph, the activity of pepsin, trypsin, lipase, and α-amylase rapidly increased, suggesting that the digestive system might have become functionally integrated. After reaching enzyme activity peaks, alkaline phosphatase, lipase, and α-amylase decreased significantly while pepsin and trypsin initially decreased and then increased to a second peak at 50 dph (25.0 ± 4.6 mm, TL). Except for the esophageal sac, the ontogeny of the digestive system in silver pomfret larvae appears to be generally similar to that of other marine fish species; it might be feasible to begin weaning this species from 15 to 20 dph, which would reduce the amount of live food as required by current protocols. This study provides a preliminary insight into the digestive system ontogeny of silver pomfret and establishes an initial step towards the rearing and weaning process optimization of this novel species.