Abstract
The experiments were conducted in order to evaluate the effectiveness of polyculture for reducing the excess organic load in prawn culture system. We determined the nitrogen budget on prawn monoculture and polyculture combining giant tiger prawn and green mussel in concrete tanks and earthen ponds in Thailand. In the concrete tanks, with an area of 17-23m2, conversion ratios of feed's nitrogen to prawn in a stocking density of 20 ind/m2 were 21% in polyculture and 16% in monoculture. Ratios of the discharge were 52 and 66%, respectively. Assimilation by green mussel was estimated at 0.2% of total fed nitrogen. In earthen ponds, 6, 700m2 for polyculture and 8, 200m2 for monoculture in 20 ind/m2, prawn outputs were 20.9 and 22.0% of feed's nitrogen. Sediment outputs were 41.3 and 49.0% and effluents were 21.0 and 14.8%, respectively. Green mussel assimilated 2.1% of feed's nitrogen. Polyculture of giant tiger prawn and green mussel let reduce the amount of organic nitrogen in bottom sediment compared with prawn monoculture, whereas the effluent's nitrogen showed reverse result. Green mussel would act as a accelerator of nutrient cycling rather than retention of nutrient in its body.
