Optimal mud to sand ratios in sediment for sea cucumber aquaculture as revealed by carbon stable isotopes

Sediment, which is central as a sink for organic material and nutrient cycling, provides habitat for feeding, resting, and nesting of sea cucumbers in aquaculture systems. We conducted a 2 mo experiment to investigate the optimal sea mud to sand ratios in sediment for sea cucumber Apostichopus japonicus (Selenka, 1867) aquaculture. Sea mud (<0.08 mm) and sand (0.08−0.5 mm) were used to prepare 5 different sediment formulations with different sea mud:sand ratios: 3:1, 1:1, 1:3, 1:0, and 0:1. Sea cucumbers were cultured in 20 fiberglass tanks (50 l) with 5 cm thick sediment spread on the bottom. Results showed that the specific growth rate of sea cucumbers and the contribution of the seaweed Sargassum muticum to food uptake by sea cucumber in the 3:1 ratio group were significantly higher than in the 1:0, 0:1, and 1:3 ratio groups, while no significant differences were observed between the 3:1 and 1:1 ratio groups. Furthermore, the total nitrogen, total organic carbon, and ammonium contents of the 1:1 and 3:1 ratio groups significantly decreased with time. These findings suggest that sea mud:sand ratios of 1:1 and 3:1 are optimal in sediment for A. japonicus aquaculture and effectively promote growth and bio remediation.