Effects of adding salt to the diet of Asian sea bass Lates calcarifer reared in fresh or salt water recirculating tanks, on growth and brush border enzyme activity

The Asian sea bass is a carnivorous, euryhaline species originating in seawater. It is currently being reared under intensive conditions in fresh and brackish water recirculating ponds. The effects of feeding sea bass a diet containing different levels of salt (NaCl) were evaluated in closed recirculating tanks in either fresh or salt (20%) water rearing conditions. Under freshwater conditions, the addition of salt to the diet resulted in a significant improvement in the feed conversion ratio (FCR), and had no effect on carcass composition of the fish. Under saltwater (20%) rearing conditions, it had no affect on either growth or FCR. The addition of salt enhanced the activity of the brush border enzymes alkaline phosphatase, lactase, and, to some extent, leucine amino peptidase in fish reared in freshwater, with the most pronounced effect exhibited in the pyloric caeca. The overall activity level of the brush border enzymes of fish reared in saltwater was found to be higher than that of the fish reared in freshwater. Fish reared in saltwater exhibited significant higher enzymatic activity of maltase, sucrase, and gamma-glutamyl transpeptidase when fed a diet with added salt compared to the control treatment. The results show that the addition of salt to the diet of Asian sea bass reared in freshwater at a level of up to 4% leads to better feed utilization coupled with a reduction in feed cost. (C) 2005 Elsevier B.V All rights reserved.