Effects of different feeding levels during day and/or night on growth and brush-border enzyme activity in juvenile Lates calcarifer reared in freshwater re-circulating tanks

The Asian sea bass is a carnivorous, euryhaline species originating in seawater. It is currently being reared under intensive conditions in freshwater re-circulating ponds. The effects of feeding juvenile Asian sea bass at different levels during the day and/or night on their growth performance and on the activity of the brush border enzymes were evaluated in closed, freshwater re-circulating tanks. Contrary to previous published data, the results of the present study showed that the feeding time factor had almost no affect on fish growth rate. Asian sea bass appear to consume food whenever it is fed, even during the night. However, the feeding ration significantly affected growth rate. Restricted feeding (2% of body mass per day) significantly reduced growth rate, while feeding in excess (6% of body mass per day) did not improve it compared with a daily ration of 4%. The feeding ration also had an impact on survival, which was significantly lower in the groups which were fed 2% of body mass (during either the day or night) than in the other groups. The coefficient of variance (CV) of weights was influenced by both the feeding level and the time of feeding. It increased as the feeding ration decreased and also when the ration was fed at night. Feeding 4% during both day and night resulted in a similar growth rate to that obtained with either day or night feeding at this level. The brush border enzyme activity was affected by both the feeding time and ration. It was higher in groups fed 2% of body mass and in groups fed during the day. The proteases were affected to a greater extent than the carbohydrases. The high activity of all the tested enzymes in the pyloric caeca points towards their major importance in food digestion and absorption in this species.