A greenhouse experiment on growth and yield effects in integrated rice-fish culture

To study the interaction between rice and fish growth in integrated culture we performed a greenhouse experiment with three treatments: (1) rice combined with a single culture of common carp, Cyprinus carpio, L., (2) rice combined with a mixture of common carp and Nile tilapia, Oreochromis niloticus (L.) and (3) rice only. The rice fish treatments were supplied with a supplementary feed, whereas the rice only was supplied with mineral fertilizer. Monitoring of growth and yield variables was accompanied by continuous determination of water characteristics. Integration of fish resulted in a significant decrease of the afternoon floodwater pH and dissolved oxygen levels, especially in the carp/tilapia treatment (p<0.05). Likewise that treatment had a lower chlorophyll-a level than the carp culture. Rice growth and yield exhibited controversial effects between the rice-fish treatments. While the carp culture had a rice yield-promoting tendency, the carp/tilapia culture rather affected rice yields negatively as compared to rice only. Differences between the rice-fish treatments were statistically significant (p<0.05) for the rice stem yield, rice straw yield, and total rice aboveground biomass yield. In contrast to the rice yields, the total fish yield was significantly higher in the carp/tilapia group compared to the carp culture. Within the carp/tilapia treatment, tilapia proved to be highly superior in the interspecific competition for feed with carp, as reflected in a significantly higher metabolic growth rate (10.8 g kg(-0.8) day(-1) vs. 4.4 g kg(-0.8) day(-1)) and body lipid content (14.7% vs. 4.4%). Analysis of nitrogen and phosphorus of the harvest fractions revealed a different N and P budget of the rice-fish treatments: while the carp treatment bad a higher absolute amount of N and P in the rice biomass, the carp/tilapia group had more N and P in the fish body mass. We conclude that there is a trade-off between rice and fish yield in integrated culture with high fish stocking density and input of supplementary feed. The fish species composition stocked seems to be crucial for the productivity of the rice-fish system. (C) 2004 Elsevier B.V. All rights reserved.