An experimental study on closed-polyculture of penaeid shrimp with tilapia and constricted tagelus

摘要

The study was conducted in 1997 to optimize the structure of the tri-species polyculture of Chinese penaeid shrimp (Penaeus chinensis), Taiwan red tilapia (Oreochromis mossabicus X O. niloticus) and constricted tagelus (Sinonovacula constricta), and to measure its efficiency. The experiment was conducted with land-based experimental enclosures set in one pond. Shrimps in all the enclosures were stocked at a density of 7.2 individual/m(2), While fish and tagelus were stocked at five different combinations, 0 tilapia: 20 tagelus/m(2), 0.08 tilapia: 14 tagelus/m(2), 0.12 tilapia: 10 tagelus/m(2), 0.16 tilapia: 7 tilapia/m(2), 0.24 tilapia: 0 tagelus/m(2). The enclosures for the shrimp monoculture were used as controls. There were no significant differences in pH, dissolved oxygen and nutrient concentrations among the treatments and control throughout the experiment, while COD in the control was significantly higher than in the polyculture treatments, Chl. a in the control was significantly higher than in the tri-species polyculture treatments, and the transparency in the control was significantly lower than in the polyculture treatments (P < 0.05). For the sizes tested (2-cm shrimp, 150-g tilapia, 3-cm tagelus), the best stocking rate was 7.2 shrimp/m(2), 0.08 tilapia/m(2) and 14 tagelus/m(2). This system can significantly raise both the culture profit and ecological efficiency. The total conversion efficiency of input nitrogen and phosphorus in the system was 23.4% and 14.7%, respectively.