Feeding habits of giant trevally Caranx ignobilis (Carangidae) rearing in floating cage nets

Abstract

Abstract The aim of this research is to determine the amount of trash fish the fish need for growth, and possible saving strategies through reducing the amount of feed until the minimum requirement is reached. Bubara fish C. ignobilis was reared in aquatec floating cages, each cage measuring 3 m × 3 m × 3m. In this study, the fish were reared in four smaller bags, with the size 1.5m × 1.5m × 1.5m placed in one large bag. As many as 75 fish with varying sizes were placed in a small bag, while 20 selected fish were allowed to measure. Fish that are placed in small bags vary in size with a length of 9.56 - 11,125 cm (TL) and a weight of 6.5 - 8.7 g. Each small bag was given different treatments, successively as follows: three day fasting - three day eating (T3), four day fasting - four day eating (T4), and five day fasting - five day eating (T5). Fish are fed 10 -15% of the total biomass, at 8:00 a.m. and 5:00 p.m. daily for 70 consecutive days. Every week, the measurement of waters parameters is carried out to determine the condition of the waters that support aquaculture activities. The results showed that there was weight gainned in the three treatments which were stated based on the absolute growth rate in weight (AGR): 0.65 g.day -1 in T3 treatment; 0.77 g.day -1 in T4 treatment; and 0.80 g.day -1 in T5 treatment. Bubara fish C. ignobilis also had the best survival rates during the rearing period even though they were treated without food with the survival rates of 90 - 95%. The efficiency of feed utilization as stated by the FCR shows that the treatment without food (fasting treatment) can be used as a mode to reduce feed spending. Treatment without food is also able to increase the number of small intestinal villi to expand the absorption surface, so that more feed is used compared to those left to rot at the bottom of the bag.