An 84 d experiment was carried out to investigate the impact of sea cucumber Apostichopus japonicus (Selenka) bioturbation on different phosphorus forms and phosphorus sorption characteristics in the sediment. Sea cucumbers were cultured in fiberglass tanks (30 × 40 × 50 cm) with 5 cm thick sediment, and were divided into 4 groups according to culture densities, i.e. 0, 4, 6, and 8 ind. tank −1. For each of these 4 densities, 4 replicates of sea cucumbers were cultured. Results showed that the increasing culture density significantly increased the content of NaOHextractable P (NaOH-P) and decreased the content of organic phosphorus (OP) in sediment. Phosphorus maximum buffer capacity (MBC) and energy adsorption (K f) values of sediment in the lower density groups (0 and 4 ind. tank −1) decreased significantly with time, while no temporal changes were observed in MBC and K f values of sediment in the higher density groups (6 and 8 ind. tank −1). Sea cucumbers facilitated the decomposition of OP and the formation of NaOH-P in sediment, and improved the ability and capacity of phosphorus sorption of the sediment with increasing culture density. Our results suggest that the use of sea cucumbers may help to prevent eutrophication in integrated multitrophic aquaculture systems.

A 70-day experiment was conducted to examine the effects of different macroalgal meals and lipid sources on growth, body wall composition and fatty acid (FA) profile of sea cucumber Apostichopus japonicus. Two macroalgal meals including Sargassum muticum (SM) and Gracilaria lemaneiformis (GL) and two lipid sources including fish oil (FO) and vegetable oil (VO) were formulated into four diets, i.e., S. muticum and fish oil (SF), S. muticum and vegetable oil (SV), G. lemaneiformis and fish oil (GF) and G. lemaneiformis and vegetable oil (GV). The results showed that the specific growth rates (SGR) of A. japonicus fed diets containing SM were significantly higher than those fed diets containing GL. No significant differences in SGR between the FObased and VO-based groups were observed. Similar results were observed in the body wall lipid content. Most body wall FAs changed to resemble the dietary FA proportions because of the dietary effect. Concentrations of 20:4n-6 of the SF and GF groups were significantly lower than the SV and GV groups, while levels of 20:5n-3 and 22:6n-3 were significantly higher than the SV and GV groups. The n-3/ n-6 polyunsaturated fatty acids (PUFA) ratios of the SF and GF groups were significantly higher than the SV and GV groups. Moreover, the SF group had significantly higher 20:5n-3 and 22:6n-3 contents and n-3/n-6 PUFAs ratio than the GF group.These findings reveal that the SF diet can show beneficial effects on both growth performance and body wall n-3 PUFAs content of A. japonicus.

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