EFFECTS OF THE SALINITY ON THE GROWTH PERFORMANCE AND DIGESTIVE ENZYME ACTIVITIES OF ANGUILLA MARMORATA ELVER AND A. BICOLOR PACIFICA ELVER

In this study, we investigated the effects of salinity on the growth and the activities of the digestive enzymes of Anguilla marmorata elver body weight (9.76 0.36) g and A. bicolor pacifica elver body weight (11.82 0.04) g. Subjects of the two species were cultured at four salinities (0, 5, 10 and 18) for 30 days. We first weighed all the eels in each tank, and then analyzed three types of digestive enzymes (protease, amylase and lipase) in three digestive organs (liver, stomach and intestine) of both species. The results showed that the survival rates of the two species were both 100% in all four salinities with no death case. In fresh water both species exhibited excellent growth performance, the highest specific growth rates (SGR), and the lowest food conversion ratios (FCR). The effects of salinity on the digestive enzyme activities were different between the two species. In the three digestive organs, the salinity did not significantly affect the activity of protease in A. marmorata elver (P0.05), but the increase in salinity caused reduced activities of amylase and lipase. For A. bicolor pacifica elver, the highest activity of protease in the stomach and the liver appeared at the salinities of 10 and 18 respectively; whereas the salinity did not affect the activities of amylase and lipase in the three digestive organs (P0.05). We deducted that saline water could inhibit the activities of amylase and lipase in the liver, the stomach and the intestine of A. marmorata elver, but might increase the protease activity of A. bicolor pacifica elver. At the same salinity the same digestive enzymes in different digestive organs showed different activities. For both species the activities of amylase and lipase in the intestine were significantly higher than in the liver and the stomach (P0.05); the activity of protease in the stomach was insignificantly higher than in the liver and the intestine (P0.05). Our study suggested that the high activity of lipase enabled A.marmorata elver and A. bicolor pacifica elver to digest fat efficiently. Therefore it may be suitable to increase the portion of the crude fat in the compounding feed, which could boost the digestion and absorption of nutrients and thus improve the quality of aquaculture.