Effects of the diatom Cylindrotheca fusiformis on the growth of the sea cucumber Apostichopus japonicus and water quality in ponds

The effects of supplementation with the benthic diatom Cylindrotheca fusiformis on the growth of the sea cucumber Apostichopus japonicus and water quality was studied in six sea cucumber culturing ponds (600 m(2) each) from November 2011 to November 2012. The nutrients for sea cucumbers in the control group were supplied solely by the spring tide inflow; whereas, in the experimental group, C. fusiformis diatoms were also added as feed. Total nitrogen and total phosphorus in the water in the diatom-supplemented group were not significantly different from the control group (P > 0.05). At one time point (October), the NH4-N in the diatom-supplemented group was lower than that in the control group (P < 0.05). The specific growth rate and biomass per unit area of sea cucumbers in the diatom-supplemented group were significantly higher than that in the control group in June (P < 0.05), and the biomass per unit area of sea cucumbers followed a similar trend in November (P < 0.05). Nevertheless, the advantages accumulated at the early stage were non-significant by the end of the experiment (P > 0.05). The economic benefits in the diatom-supplemented group were 10.9 % higher than that in the control group. The results suggest that fresh C. fusiformis can serve as an important food resource for sea cucumbers during the early growth stages. Therefore, supplementation with fresh C. fusiformis may be effective for increasing water quality and sea cucumber production, as C. fusiformis can provide food for aquaculture animals and utilize nitrogen and phosphorus in the water.