Search

Reproductive success is unpredictable for many cultured echinoderms. And cost of reproduction plays an important role in animal life-history. Therefore, understanding cost of reproduction contributes to improving breeding techniques during broodstock rearing in aquaculture. In this study, energetic costs during breeding were explored in the sea cucumber, Apostichopus japonicus, an important aquaculture species in China, Japan and South Korea. The food intake, digestive functions and energy budget patterns were estimated at different breeding stages. Unexpectedly, in the growing gonad phase of the sea cucumber lifecycle, animals showed a decline in feed consumption (from 4.49 to 2.6 g ind-1 day-1), ingestion rate (from 0.4 to 0.13 g g-1 day-1) and apparent digestive rate (from 14.73% to 10.92%), resulting in a reduced energy input. In addition, the increased energy investment in reproduction (from 1.76% to 15.61%) resulted in a decrease in energy allocated to soma growth (from 17.1% to 5.64%) and self-maintenance (from 47.82% to 34.67%). These results suggest that reproduction impairs energy acquisition ability in breeding A. japonicus. And broodstock can adapt energy shortage by internal adjustment of energy allocation strategy. [ABSTRACT FROM AUTHOR]

Ascorbic acid plays an important role in the growth and immunity of the sea cucumber, Apostichopus japonicus , a valuable commercial species in China, South Korea, and Japan. In this study, we investigated the dietary ascorbic acid requirements of two newly discovered color morphs of A. japonicus , white and purple, and compared them with that of the common green morph. Six test diets were formulated containing 0, 50, 100, 200, 400, and 800 mg ascorbic acid equivalent per kg, as l-ascorbyl-2-polyphosphate. The color morphs were fed the test diets for 60 days, and their growth, energy budget, and immunological performance recorded. Dietary ascorbic acid levels had a significant effect on the growth of A. japonicus ( P < 0.001). The green and purple morphs showed the greatest specific growth rate (SGR), ingestion rate (IR), and food conversion efficiency (FCE) at a dietary ascorbic acid level of 200 mg/kg, while maximum values for the white morph were recorded at 100 mg/kg, indicating a lower ascorbic acid requirement in the white morph than the green and purple morphs. This could be due to the lower growth and metabolic rates recorded in the white morph, whose SGR, IR, and FCE values and immune indicators were lower than the green and the purple morphs. Malonaldehyde (MDA) content of the coelomic fluid was significantly lower when dietary ascorbic acid was ≥200 mg/kg ( P < 0.05). Superoxide dismutase (SOD) and catalase (CAT) activities, and total anti-oxidative capacity (T-AOC) were generally higher at dietary ascorbic acid levels of 100, 200, and 400 mg/kg compared with the other treatments. SOD and CAT activities and T-AOC were significantly and positively correlated with SGR, indicating that supplementary dietary ascorbic acid had a beneficial effect on growth and immunity. SGR, energy intake, and the proportion of energy allocated to growth decreased significantly in the white and purple morphs when ascorbic acid levels reached 800 mg/kg ( P < 0.05); as did those of the green morph, but not to a significant level. Immune indicators decreased and MDA content increased slightly at 800 mg/kg, indicating that high levels of dietary ascorbic acid do not benefit growth or immunity. The SOD and CAT activities were higher in the purple morph than the green and white morphs, indicating its superior immune system capacity. Optimum growth and immunity of A. japonicus were achieved at ∼100 mg/kg of ascorbic acid in the white morph and 200 mg/kg in the green and purple morphs. [ABSTRACT FROM AUTHOR]

Protein is a necessary nutrient for the sea cucumber, Apostichopus japonicus , an important commercial species in China, South Korea and Japan. In this study, the dietary protein requirements of two newly discovered color morphs—white and purple was investigated and compared with the common, green morph. The green, white and purple morphs were fed a diet with five different protein levels (1, 6, 11, 16 and 21%) for 60 days with a mixture of soybean meal and fish meal (1:1) as the protein source, and their growth, energy budget, physiological and immunological performance were measured. Results showed that dietary protein levels had a significant effect on the growth performance of A. japonicus (P < 0.05). The maximum specific growth rate (SGR) and proportion of energy allocated for growth occurred at dietary protein levels of 6 and 11%, and the food conversion efficiency (FCE) was highest at the 11% protein level, indicating that the optimum dietary protein level for these color morphs is at ~ 11%. Apparent digestibility coefficients for dry matter (ADMD) and crude protein (ACPD) increased, but the ingestion rate decreased with increasing dietary protein levels, due perhaps to the decreased sea-mud content of the diets. The energy allocated to excretion, and the free ammonia and malonaldehyde content in coelomic fluid increased with increasing dietary protein levels, which can be explained by enhanced protein metabolism. Trypsin activity decreased significantly when dietary protein was > 16%, indicating that the protein content was beyond the digestive ability of sea cucumber, and that excess protein in the diet inhibits protein digestion. Catalase (CAT) and glutamic–oxaloacetic transaminase activity was positively and significantly correlated with SGR, indicating that rapid growth was supported by a robust immune system and effective protein metabolism. At a 1% dietary protein level, the purple color morph had significantly higher SGR, FCE, ACPD and CAT activity, and allocated more energy for growth than the green morph, indicating that the purple morph may be better adapted to a low protein diet than the green morph. The white morph had lower SGR, FCE, superoxide dismutase (SOD) and CAT activity, and allocated less energy to growth, but had a higher excretion energy and higher free ammonia content in coelomic fluid than the green or purple morphs, indicating a difference or physiological defect in protein metabolism in the white morph. Statement of relevance The results of this study would be invaluable in improving aquaculture technology and management strategies for green, white, and purple color morphs of Apostichopus japonicus . [ABSTRACT FROM AUTHOR]