Research Of Differences In Environmental Adaptability, And Nutritional Requirements Of Three Color Morphs Of Sea Cucumber, Apostichopus Japonicus(selenka)

The sea cucumber Apostichopus japonicus(Selenka) is a sediment feeder, inhabiting in Asian temperate coasts from a latitude of 35 ?N to at least 44 ?N. This species has been exploited as an important fishery resource in Russia, China, Japan and Korea, due to its aphrodisiac and anticancer properties. In recent years, sea cucumber farming has grown rapidly at many places in China, such as Dalian, Weihai, Yantai and Qingdao, to meet the increasing demand for dried holothurian products in the market. Undoubtedly, this farming practice effectively protects the natural sea cucumber resource from overfishing. However, with the rapid development of sea cucumber aquaculture, serious problems with disease and breed deterioration have emerged, due to inappropriate brood stock management and inbreeding. Selecting good breeding lines is a major issue for sea cucumber aquaculture, and body color selection is particularly important, along with growth and disease resistance. Color variation is a distinct characteristic of A. japonicus and body color can affect the taste and market price of holothurian products. Apostichopus japonicus can generally be divided into three color morphs: black, red and green. Two new color morphs, white and purple A. japonicus were recently found on the coast of the Rushan, Weihai area, and their progeny were successfully cultivated in the cooperative aquaculture base at Weihai City, China. A detailed literature review of physiological and ecological adaptability, and nutritional requirements of sea cucumber, Apostichopus japonicus was undertaken. It was found that the previous results are quite different because of the different experimental conditions, and although the marketing potential of white and purple morphs is enormous, no information is available on the environmental adaptability and nutritional requirements of these two new color morphs. In this research, a series of experiments were conducted to study the differences in physiological and ecological adaptability, and nutritional requirements ofthree color morphs of sea cucumber, Apostichopus japonicus--- green, white, and purple color morphs. Such information could be helpful in improving aquaculture technology and management for these three morphs of A. japonicus. The main results are as follows:1. Effect of temperature on growth, energy budget and physiological performance of different color morphs of sea cucumber, Apostichopus japonicusAs an intertidal species, the sea cucumber Apostichopus japonicus(Selenka), tolerates diel and seasonal temperature fluctuations. This study was conducted to compare the performance of green, white, and purple color morphs of A. japonicus at different water temperatures to help improving aquaculture technology and management. In this study, three color morphs of juvenile A. japonicus(1.5 ? 0.1 g) were cultured at 10 ?C, 14 ?C, 18 ?C, 22 ?C and 26 ?C for 60 days. The influence of temperature on the growth, energy allocation and physiological performance of A. japonicus was determined. The results indicated that temperature had a significant effect on growth, energy allocation and the physiology of sea cucumbers(P <0.05). Specific growth rates, feed conversion efficiencies and the proportion of energy allocated to growth of all three color morphs of A. japonicus were optimal at 18 ?C, while ingestion rates and energy intake reached a maximum at 22 ?C. Oxygen consumption rate and lysozyme activity increased in sea cucumbers as temperature increased. Activities of the enzymes superoxide dismutase, hexokinase and trypsin generally reached a maximum in all three color morphs of A. japonicus at 18 ?C. The purple morph of A. japonicus had a higher growth rate, food conversion efficiency, and proportion of energy allocated to growth than green and white morphs at 18 ?C and 22 ?C. This can be explained by the much higher trypsin activity in the intestine of purple morph, which may also be the main reason for the high superoxide dismutase activity in the purple. At temperatures of 18 ?C, 22 ?C and 26 ?C, the green morph had the highest level of lysozyme activity and purple morph had the lowest. These results indicated that the green and white color morphs may be more susceptible to thermal stress than the purple. Ingestion rates and energy intake of white morph were low compared with the green and purple at 10 °C, 14 °C, 18 °C and 22 ?C, suggesting that white A. japonicus feed less actively. In conclusion, the optimum temperature for culture of the three color morphs was around 18 °C, and the purple had a better tolerance of thermal stress, which deserves further study and application.2. The effect of salinity on the growth, energy budget and physiologicalperformance of different color morphs of sea cucumber, Apostichopus japonicus The sea cucumber Apostichopus japonicus(Selenka) tolerates salinity fluctuations when inhabiting the intertidal zone and culture ponds. Color variation is a distinct characteristic of A. japonicus, and a new color morph, purple A. japonicus was recently found on the coast of Rushan, Weihai City. 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 growth, energy allocation and the 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 highest in purple, then green and 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 the 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.3. Effects of dietary protein levels on the growth, energy budget, and physiological and immunological performance of different color morphs of sea cucumber, Apostichopus japonicusProtein 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.4. Effects of dietary ascorbic acid levels on the growth, energy budget, and immunological performance of different color morphs of the sea cucumber, Apostichopus japonicusAscorbic 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, the dietary ascorbic acid requirements of two newly discovered color morphs of A. japonicus, white and purple, were investigated, and compared with that of the common green morph. Six diets were formulated containing 0, 50, 100, 200, 400, and 800 mg ascorbic acid equivalent kg-1 diet, as L-ascorbyl-2-polyphosphate. The color morphs were fed the diets for 60 days, and their growth, energy budget, and immunological performance recorded. Results showed that dietary ascorbic acid levels had a significant effect on the growth performance of A. japonicus(P <0.05). The green and purple morphs had the maximum specific growth rate(SGR), ingestion rate(IR), and feed conversion efficiency(FCE) at a dietary ascorbic acid level of 200 mg kg-1, while maximum values for the white morph were recorded at 100 mg kg-1, indicating that the white morph had a lower ascorbic acid requirement than the green and purple morphs. This could be explained by the lower growth and metabolic rates of the white morph, with lower SGR, IR, and FCE values plus immune indicators than the green and the purple morphs. Malonaldehyde(MDA) content in coelomic fluid decreased significantly when dietary ascorbic acid was ≥200 mg kg-1(P <0.05). Superoxide dismutase(SOD), catalase(CAT), and lysozyme activities, plus total antioxidative capacity(T-AOC) leveled out at 100–400 mg kg-1. SOD and CAT activities plus T-AOC were significantly and positively correlated with SGR(P <0.05), indicating that supplemental 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-1(P <0.05); as did those of the green morph, but not significantly so. Immune indicators decreased and MDA content increased slightly at the 800 mg kg-1 level, indicating that high dietary ascorbic acid does not benefit growth or immunity. SOD and CAT activities were higher in the purple morph than the green and white morphs, indicating its superior immune system condition. Considering optimum growth and immunity, the ascorbic acid requirement of A. japonicus was ~100 mg kg-1 for the white morph and 200 mg kg-1 for the green and purple morphs.