Ontogeny of the digestive enzymes in butter catfish Ompok bimaculatus (Bloch) larvae

Abstract

The digestive physiology of butter catfish was studied by assessing the activity of different pancreatic (trypsin, chymotrypsin, α-amylase and lipase), gastric (pepsin) and intestinal (alkaline phosphatase) enzymes from hatching until the juvenile stage (30 dph). Larvae were reared at 27 °C and fed with Artemia nauplii from 2 days post hatching (dph) until 10 dph, from 7–10 dph with Artemia nauplii and zooplankton (Cyclopoida) and from 10 dph onwards only with zooplankton. The assessment of the activity of digestive enzymes showed that enzymes involved in the digestion of proteins, lipids and carbohydrates were present in butter catfish larvae before mouth opening and increased after the onset of exogenous feeding, coinciding with the histological organization of the exocrine pancreas. The specific activity of most of the pancreatic enzymes increased until 15 dph and decreased thereafter coinciding with the increase of pepsin. A progressive shift in activity from alkaline (trypsin and chymotrypsin) to acid (pepsin) proteases indicated a change in the digestive physiology of the specimen, as alkaline proteases were no longer the main digestive enzymes involved in protein digestion after the onset of acidic digestion between 15 and 21 dph. The maturation of the intestine and the achievement of a juvenile-like mode of digestion were demonstrated by changes in enzyme activities from the exocrine pancreas and stomach that coincided with alterations in enzyme production occurring in the intestine (e.g. alkaline phosphatase). Considering the ontogenetic development of the digestive enzymes from the pancreas, stomach and intestine, butter catfish larvae might be weaned between 15 and 21 dph, as larvae have achieved the complete maturation of their digestive capacities. These results contradict previous recommendations, which were based solely on the histological organization of the gastric gland and histochemical properties of mucous cells from the stomach, to wean butter catfish larvae at earlier ages. These findings on the functional development of the digestive system in butter catfish would be useful to improve the actual larval rearing techniques for this promising catfish species from the Indian sub-continent.