Effects of water temperature on activities of digestive enzymes of juvenile Acipenser schrenckii

Sturgeon culture has been developed in the last decade.Some researchers have investigated effects of temperature on digestive enzyme activities in different fish.But the effect of water temperature on digestive enzyme activities in juvenile Acipenser schrenckii is still little known.The purpose of this study was to investigate the effects of water temperature on activities of three kinds of digestive enzymes(protease,amylase and lipase) in digestive organs(pyloric caecum,ileum,duodenum,stomach and liver) in juvenile Acipenser schrenckii.Under three different water temperatures(14 ℃,21 ℃,28 ℃) and in culture tanks,juvenile sturgeon[initial body weight:(124.20±15.12)g] were cultured for 10 days respectively.During the experimental period,water temperature,pH,DO and ammonia-N were measured once a day.The major environmental factors were controlled at the same levels in each experimental tank,where DO was beyond(6.0 mg/L) and pH was 7.4±0.4.After starvation for 24 h,fish were sampled randomly and killed for enzyme activity assay.Eighteen fish were sampled in each group.Fish were dissected on ice and the alimentary canal and liver were cleaned,with chilly saline water.The alimentary canal was separated into stomach,pyloric caecum,duodenum and ileum portions and kept in liquid nitrogen.The digestive organs were minced and homogenized separately in 10 volumes of 0.65% cold sodium chloride solution by weight of the minced tissue.Each homogenized sample was then centrifuged at 1 700 g for 20 min and the supernatant was collected and prepared for enzyme assay at 4 ℃.The results showed that:1)the activities of protease in pyloric caecum,ileum and liver were the highest at 21 ℃(P0.05),while those in duodenum and stomach were the highest at 28 ℃(P0.05) and those in all examined digestive organs were the lowest at 14 ℃(P0.05);2)the activities of amylase in all examined digestive organs were the highest at 21 ℃(P0.05),while those in pyloric caecum,ileum and duodenum were the lowest at 28 ℃(P0.05),and those in stomach and liver were the lowest at 14 ℃(P0.05),respectively;3)the activities of lipase in all examed digestive organs were the highest at 14 ℃ and lowest at 28 ℃(P0.05).The activity order of protease and amylase in all examined digestive organs from high to low was pyloric caecum,ileum,duodenum,stomach and liver at 21 ℃.Protease and amylase activities in ileum were higher than that in duodenum at 14 ℃(P0.05),but lower than that in duodenum at 28 ℃(P0.05).Simultaneously,the activity order of lipase in all examined digestive organs from high to low was ileum,duodenum,stomach,liver and pyloric caecum at 14 ℃ and 21 ℃,While,the activity of lipase in ileum was lower than that in duodenum at 28 ℃(P0.05).The results indicated that juvenile amur sturgeon had good digestion on lipid at 14 ℃,on protein at 21 ℃ and 28 ℃.However,juvenile amur sturgeon had poor digestion on carbohydrate at all experimental water temperatures.Accordingly,the lipid level in the diet should be increased at 14 ℃,while the protein level in the diet should be increased at 21 ℃ and 28 ℃ water temperatures.[Journal of Fishery Sciences of China,2007,14(1):126-131]