Effects of white shrimp, Litopenaeus vannamei (Boone), and Nile tilapia, Oreochromis niloticus L., stocking density on growth, nutrient conversion rate and economic return in integrated closed recirculation system

Integrated closed recirculation systems in intensive shrimp culture is one strategy that minimizes waste from culture systems and the risk of disease and provides an additional income source as well. This study investigated the effect of tilapia-shrimp stocking density ratio on the growth, nutrient conversion rate and economic return in the integrated closed recirculation culture system of white shrimp (Litopenaeus vannamei) and Nile tilapia (Oreochromis niloticus). The experiment was conducted using outdoor tank system with 6 treatment conditions: T1, single shrimp tank system; T2, closed recirculation system without tilapia; T3 to T6, integrated closed recirculation system with the tilapia-shrimp stocking density ratio of 0.01, 0.025, 0.05 and 0.075, respectively. The shrimp were stocked at a density of 40 individual m(-2) for all treatments. Shrimp were fed with commercial pellets, while tilapia was not fed with the feed pellet. The culture period was 8 weeks for shrimp and 7 weeks for tilapia. The shrimp growth rate and net income of the system of T2 was significantly higher than T5 and T6 (P<0.05) but was no different from T1, T3 and T4. The tilapia growth rate in T3 was significantly higher than the others (P<0.05). The nitrogen conversion rate into total (shrimp + tilapia) biomass of T2 to T5 was significantly higher than T1 (P<0.05). T6 showed a lower N conversion rate than the lower tilapia-shrimp ratio. The phosphorus conversion rate into total biomass was significantly higher in T3 to T6 than T1 and T2 (P<0.05). These results indicate that tilapia stocking significantly improved P conversion rate but the N conversion and shrimp growth rates decreased with high tilapia stocking. Considering all parameters, the integrated system with a low tilapia-shrimp ratio (the ratio of 0.01 and 0.025) were effective to improve the nutrient conversion rate to culture animals without lowering shrimp growth. (C) 2007 Elsevier B.V. All rights reserved.