Two experiments were conducted at CelAgrid, Kandal Province for a period of 80days.
In experiment 1, 12 ponds each with area of 10m2 were used to compare four treatments arranged in a 2 x 2 factorial with a completely randomized design with 3 replicates. The first factor was fertilizer with effluent and no effluent; the second factor was stocking density of 3 or 5 fish per m2. The fish in each pond were provided with feed at 5% of the fish biomass (DM basis). The feed contained 25% of water spinach, 25% of duck weed and 50% of rice bran (DM basis). The effluent from a bio-digester was applied every 7 days, at rates equivalent to 150 kg N/ha.
Survival rate was higher in ponds fertilized with effluent and in ponds with lower fish density. There were no differences for gain in weight and length due to treatment, and no interaction between fertilizer and stocking density. However, these data were derived from random samples of fish taken at 20 day intervals and the results were partially confounded by differences among treatments in survival. Net fish yield was higher for the higher stocking density but there was no effect of fertilization with effluent. Feed conversion (DM offered/net fish yield) did not differ among treatments but this measurement was also confounded by differences in survival as amounts of feed offered were based on initial numbers of fish and the average weight estimated from the sampling at 20 day intervals. Final fish weight and net fish yield were negatively correlated with survival rate.
In experiment 2, 12 plots in a paddy field each with an area of 209m2 were used to compare 4 treatments in a 2 x 2 factorial in a completely randomized design with 3 replicates. The first factor was with or without feed supplement; the second factor was different stocking densities of 3 or 5 fish per m2. In each plot of paddy there was a trench 11m wide x 1m in length x 1m deep along one side of each plot. The feed supplement was the same as in experiment 1. All paddy plots were fertilized with effluent from a bio-digester every 7 days at the rate of 150 kg N per ha.
Survival rate was not affected by supplementation but there was a tendency (P = 0.10) for it to be lower on the higher stocking rate. Both final weight of fish and the net fish yield were increased by supplementation and by stocking rate with no interaction between the treatments. The FCR (for those paddies that received feed supplementation) was not affected by stocking rate.