Survival, growth, food availability and assimilation efficiency of the sea cucumber Apostichopus japonicus bottom-cultured under a fish farm in southern China

The survival, growth, food availability and assimilation efficiency of the bottom-cultured sea cucumber Apostichopus japonicus were investigated at a subtropical fish farm in Dapeng Cove, Daya Bay, during an 8-month field study. Our aim was to assess the possibility of producing commercial-sized A. japonicus under fish farms and developing an integrated multi-trophic aquaculture (IMTA) system on the southern China coast. Survival of A. japonicus cultured at the fish farm and reference site (1 km away from the fish farm) was 100% from December 9, 2011 through June 29, 2012, though all animals at both sites died at the July sampling because of anoxia caused by water stratification. Factors including time, culture site and stocking density had significant effects on the growth of A. japonicas. Growth during winter and early spring varied significantly with density and site; however, growth over the whole study period was significantly affected by time, site and the interactions between time/site and time/density. Specific growth rates of A. japonicus at the fish farm (0.40-0.71%) and reference site (0.15-0.54%) were always positive from winter through early spring (December to April). The faster growth recorded at the fish farm site during this period was mainly due to accessing more food of better quality from the surrounding environment. A. japonicus underwent aestivation and suffered weight loss with the increase of water temperature after the April sampling. Only A. japonicus cultured at low density (10 ind m− 2) at the fish farm site reached a commercial size (> 100 g wet weight) during the entire study period. Organic matter contents of the foregut material were higher than the surrounding sediments, indicating that A. japonicus had a high food selection capability. The assimilation efficiency of A. japonicus in the experimental areas was relatively high, with average values of 13.78 ± 5.83% at the fish farm and 15.13 ± 7.75% at the reference site. This study demonstrated that fish farm debris can be efficiently used by A. japonicus, and bottom culture is an economical and environmentally friendly system of producing commercial-sized A. japonicus in subtropical fish farms in southern China. We recommend harvesting bottom-cultured A. japonicus specimens before May, thereby avoiding weight loss during aestivation. We also suggest improving product size through enhanced seed size and/or reducing stocking density.