COMPARATIVE STUDY ON ACTIVITIES OF DIGESTIVE ENZYME IN A. SCHRENCKI,A.RUTHENUS, A.BAERI,A. GULDENSTADTI,HYBRID STURGEON AND A. SINENSIS

Adaptabilities of fish to different kinds of food and nutrient composition show that fish digestive system has the ability to adapte to food, and corresponding to these alterations the activities of digestive enzymes of fish would change greatly. Sturgeon culture has been progressing in late decade years. Some researchers have investigated the nutrition requirements and feeding regimes for different sturgeon. But literature on the digestive enzymes in sturgeon is still few The objective of the present study was to determine protease, lipase and amylase activities in six different sturgeon species: A. schrencki, A. ruthenus, A. baeri, A. guldenstadti, Hybrid sturgeon( Huso huso L. ♀× A . ruthenus ♂)and A. Sinensis. Six species of sturgeon were reared with artificial diets special for sturgeon in the Centre of Sturgeon Breeding of Chinese Academy of Fishery Sciences. Fish of similar age were selected. They wave devided in to two size groups: fingerlings(5-15g)and goung (48-250g) except for bester which had lower weight (mean of 46g). After starvation for 24 h, fish were sampled randomly and killed for the enzyme activities assays. The fish were dissected on ice and the alimentary canal and liver cleaned, washed with chilly distilled water. The alimentary canal was cut as stomach and gut portions. The stomach, liver and intestine were then minced and homogenized separately with 20 volumes of cold 0.75% sodium chloride solution to one part by weight of the minced tissue. Each homogenized sample was then centrifuged at 3500r/min for 10 min and the supernatant collected and prepared for enzyme assay at 4℃. The supernatant need be diluted with five folds before determining the protease activities in stomach or intestine. Total proteolytic activity was measured using the casein hydrolysis method. Proteolytic enzyme activity was defined as the amount of enzyme needed to catalyze the formation of μg of tyrosine per 1 min using 1g of fresh tissue at 30℃ and under pH 7.6(pH 2.2 for stomach). Amylase activity was determined by the starch hydrolysis method(BSZU, 1978). Amylase activity was expressed as mg of starch hydrolyzed using 1g of fresh tissue per 30 min at 30℃ and under pH7.6. Lipase activity was estimated in accordance with the method described in BSZU (1978). Its activity was expressed as the amount of enzyme needed to hydrolyze the lipid in 1g of fresh tissue μg of fatty acid per min at 30℃and under pH7.6. All spectrometric analyses were carried out using a Shimadzu UV-visible spectrophotometer(UV-2401 PC). All samples were assayed in triplicate with 2-3 fry fish or 1-2 fingerling fish each. The results were expressed as mean±s.d. The activities of protease, lipase and amylase in digestive organs (stomach, intestine and liver) of six species of juvenile sturgeon were determined at two growth stages. Among the three digestive organs of the six species, protease activity in intestine was the highest, but lowest in liver. Protease activity in intestine was significantly higher than those in the other two tissues ( P P >0.05);Amylase activity in intestine was the highest, and significantly higher than that of stomach or liver( PP >0.05). Except for individual differences, the activities of the three kinds of digestive enzymes were roughly the same among the six species. The results show that the intestine of tested sturgeons is the main digestive spot in digestion of food, the stomach ranks the second.