Effect of stocking densities and feed supplements on the growth performance of tilapia (Oreochromis spp.) raised in ponds and in the paddy field 

Sen Sorphea, Torbjorn Lundh*, T R Preston** and Khieu Borin

CelAgrid (Center for Livestock and Agriculture Development)
sorphea_sen@yahoo.com
*Department of Animal Nutrition and Management, Swedish University of Agricultural Science,
Uppsala, Sweeden
** UTA - TOSOLY  Finca Ecológica,    
AA # 48, Socorro, Santander, Santander del Sur, Colombia

 

Abstract 

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.

In conclusion it would seem that in rice-fish systems, supplementation is not an appropriate intervention, in view of the lower efficiency of use of the supplement. Thus, for the additional 43 kg of net fish yield (123-80) in experiment 2,  the amount of feed provided was on average  358 kg (7.5/209*10000), that is about 7.5 kg feed per 1 kg of net fish yield.   Measures that lead to enhancement of the natural feed supply (e g: fertilization with bio-digester effluent) would seem to be more appropriate technology.

Key words: Effluent, feed conversion, rice-fish culture, supplementation,