Evaluation of shrimp polyculture system in Thailand based on stable carbon and nitrogen isotope ratios

Abstract

To quantify the contribution by cocultured animals to waste assimilation in an inten- sive shrimp farm in Thailand, the food web structures of the macrobenthos in a reservoir pond, a shrimp culture pond and water treatment ponds were examined using the stable C and N isotope ratio technique. Seawater for aquaculture was drawn from a creek, and stored in a reservoir pond, used for farming the banana prawn Fenneropenaeus merguiensis in culture ponds, and then recy- cled through treatment ponds where the green mussel Perna viridis was cultured to remove organic wastes discharged from the farming. The clam worm Nereididae sp. and the mud creeper Cerithideopsilla cingulata in the culture pond had d 13 C values of -21.0‰ and -18.4‰, respectively, suggesting that shrimp feed (mean d 13 C =- 20.7‰) was the main food source for these species. The d 13 C analysis also suggested that sediments (-23.7‰) in the reservoir pond and particulate organic matter (POM) (-24.0‰) and/or sediments (-25.0‰) in the treatment pond supplied carbon for most macrobenthic animals. However, green mussels in the treatment pond had a mean d 13 C value of -20.5‰, suggesting that shrimp feed was the main food source for this species.