EFFECT OF FEEDING LEVEL ON FEED LOSSES AND FEED-UTILIZATION OF SOYA AND FISH-MEAL DIETS IN COLOSSOMA-MACROPOMUM (CUVIER)

Juvenile, l-g Colossoma macropomum (Cuvier) were fed two different die ts: one with fish meal and another with soya meal as the main dietary protein source. Both diets were provided at ad libitum feeding level, and at two restricted feeding levels of approximate to 80% and 60% of the ad libitum level. The experiment was performed in 30 aquaria, each stocked with 12 fish. For each treatment (two diets x three feeding l evels), there were five replicates, Fish were fed three times daily at 0900, 1300 and 1700 h., At sampling days (days 14, 29, 44) in each aq uarium in one of these feedings, chromic-oxide-marked feed was used. S hortly after the last meal, fish were weighed and four fish were taken from each aquarium for determination of the chromic oxide content in their digestive tract. Fish fed the fish meal diet attained a higher w eight but had a lower body protein content. At the ad libitum feeding level, feed intake of the fish meal diet was higher, but feed and prot ein utilization efficiency were lower than with the soya diet. However , statistical analysis of the data of both the ad libitum and the two restricted feeding levels revealed that the reduced voluntary feed int ake of the soya diet was the cause of its better utilization with ad l ibitum feeding. There is no evidence that soya protein is more freely available than fish meal protein, The chromic oxide data showed that 1 5 min after feeding, all of the feed (99.8%) could be traced back in f ish fed the lowest feeding level, while at the ad libitum feeding leve l the recovery was only 72%. These data confirmed the hypothesis that at high feeding levels, considerable amounts of feed remain uneaten. F eed losses were not significantly different between the two diets. The chromic oxide recovery data of the 0900 h and 1300 h feedings showed that the feed passage rate in the digestive tract was similar for the three different feeding levels. Due to the high feed losses at high fe eding levels, the relation between feed ration and feed utilization is determined mainly by the percentage of feed losses at the different f eed rations.