The effect of salinity on the growth, energy budget and physiological performance of green, white and purple color morphs of sea cucumber, Apostichopus japonicus

The sea cucumber Apostichopus japonicus (Selenka) tolerates salinity fluctuations when inhabiting the intertidal zone and culture ponds. In this study, green, white and purple morphs of juvenile A. japonicus (1.0 ± 0.1 g) were cultured at salinities of 22, 26, 30, 34 and 38 for 60 days. The influence of salinity on the growth, energy allocation and physiological performance of A. japonicus was determined. The results indicated that the three color morphs tested could survive within the salinity range of 22-38. Salinity had a significant effect on the growth, energy allocation and physiological performance of sea cucumbers (P < 0.05). Specific growth rates, ingestion rates and feed conversion efficiencies of A. japonicus were generally optimal at a salinity of 30. Similar results were obtained for energy ingested, and the proportion of energy allocated to growth. Significant changes in enzyme activities of sea cucumbers mainly occurred at salinities of 22 and 38, indicating that metabolism was affected by low and high salinities. Green A. japonicus grew faster than the white and purple color morphs at a salinity of 22. Growth rates were the highest in purple, then green and the lowest in white color morphs at salinities of 30, 34 and 38. At a salinity of 22, the green allocated more energy to growth and respiration. The purple morph allocated more energy to growth and respiration when water salinity reached 34 and 38. At salinities of 30, 34 and 38, the purple morph had higher trypsin and superoxide dismutase activities, which supported the higher specific growth rate and food conversion rates compared with the green and white color morphs. The results clearly showed that the green color morph performed better at low salinities, while the purple was better adapted to high salinities within the tolerance range.