Abstract

The experiment was conducted for 122 days in central Thailand to test rearing of hybrid catfish in cages in earthen ponds, where tipalia (Oreochromis niloticu.~) was stocked to utilize the waste products derived from intensively rcarcd catfish. Catfish fingerlings (13-17 g size) was stocked in plastic net cages at a density of 275 fish/m3. Six earthen ponds (250 m2-1 10 d each) wcre uscd to suspend the cages in two loading densities as experimental treatments: 880 and 1760 catfishlpond. Each loading density was replicated in 3 ponds. Each pond was stocked with 440 sex-reversed male tilapia of 6-7 g size in open water, giving the catfish and tilapia stocking ratios of 2:l and 4:1, respectively. Catfish was fed twice daily at 3-10 % body weight per day with commercial floating pellets containing 25-30 % crude protein. Water quality was analyzcd bi-weekly for concentration of dissolved oxygen, ammonia and chlorphyll a. Results showed that there was no significant difference (p<0.05) in catfish growth rate and survival between the two loading densities. The mean weight gain of harvested catfish was 259.5 + 34.5 g and 255.2 f 8.4 glfish, giving the total net yield of 218.0 + 26.8 kg and 391.5 f 88.0 kg per pond in low and high loading density, respectively. Tilapia was harvested with mean weight of 172.3 f 37.8 g and 297.5 f 32.0 glfish, and the net yield of 68.1 2 13.6 and 86.0 f 27.2 kglpond for low and high loading catfish density treatment, respectively. Chlorophyll a and total arnmonia concentrations differed greatly between the two treatments. Early morning dissolved oxygen (DO) declined steadily both treatments over the culture period