Effects Of Different Diets On The Feeding And Growth Of Sea Cucumber, Apsticfhpus Japonicus Selenka: Evidence From Stable Isotopes

Effect of different diets on the feeding and growth of sea cucumber, Apostichopus japonicus Selenka was studied by analysis of stable isotope model. The main results are detailed as followed:1. Selective absorption of various food sources by sea cucumber Apostichopus japonicus (Selenka) under different ration levelsAbsorption of three food sources by sea cucumber Apostichopus japonicus (Selenka) was studied under different ration levels with evidence of carbon and nitrogen stable isotopes. During three- month cultivation, the mixture of red algae Gracilaria lemaneiformis, brown algae Sargassum thunbergii and benthic matter (with dominant component of diatom) was fed to sea cucumbers. With 3 different ration levels, i.e., 1% (Diet A), 5% (Diet B) and 10% (Diet C) of the weight of experimental sea cucumber (9.56±0.03g). Results showed that sea cucumbers fed on diet A (0.25±0.08) showed the significantly lowest special growth rate (SGR) among the 3 diet groups (p<0.05) while SGRs of sea cucumbers fed on diet B or C did not show significant difference (0.69±0.04 vs 0.79±0.05, p>0.05). Calculation with carbon and nitrogen table isotope mixing model revealed that sea cucumbers fed on Diet A did not show selectivity among three sources, contribution of Gracilaria lemaneiformis, Sargassum thunbergii and benthic matter to the sea cucumber dietary consumption was 31%,35% and 34%, respectively. However, for Diet B and C, sea cucumbers showed absorption preference to benthic matter contribute (46%~70%). On the other hand, sea cucumbers also absorbed more Gracilaria lemaneiformis than Sargassum thunbergii, suggesting that Gracilaria lemaneiformis might be more preferable to the nutritional requirements of sea cucumber relative to the traditional feed Sargassum thunbergii and G. lemaneiformis might be alternative ingredient of sea cucumber feed in place of S. thunbergii. 2. Absorption of different food sources by sea cucumber Apostichopus japonicus (Selenka) (Echinodermata: Holothuroidea): evidence from carbon stable isotopeA study was conducted using diets containing 80 % different seaweeds (Sargassum thunbergii, Sargassum polycystum, Laminaria japonica leaf or thallus and Laminaria japonica root ) and 20 % yellow soil or sea mud to generate information on growth and energy budget of sea cucumber (Apostichopus japonicus). The results showed that there's no difference between diets containing the same proportion of sea mud and yellow soil. Sea cucumbers fed with diet containing the Laminaria japonica leaf or thallus had a significant lowest specific growth rate (SGR) in different four diets (p < 0.05), and there was no different in three other diets. There was a highest level on ingestion rate of sea cucumbers fed with Laminaria japonica root diet. Sea cucumbers fed diets containing Sargassum thunbergii and Sargassum polycystum showed a highest energy deposited for growth, and had significant difference from animals fed Laminaria japonica leaf or thallus and Laminaria japonica root. The energy lost in feces accounted for the majority of the energy intake, and showed a highest percent in Laminaria japonica root treatment (64.29 ~ 65.27 %).3. Effects of different protein sources on the growth and activities of digestive enzymes of sea cucumbers Apostichopus japanicusThe present experiment compared the effects of different proportions of fish meal and scallop tissue meal in the artificial diet on the digestive enzymes of sea cucumbers and analyzed the absorption efficiencies of different diet ingredients by sea cucumbers using stable isotopes as biological tracers so as to study the absorption of protein sources by sea cucumbers and evaluate the optimal proportion of animal protein in the artificial diet of sea cucumbers. Results showed the significant effects of different diets on the growth and stable isotope ratios of sea cucumbers. The highest growth rate appeared in the sea cucumbers fed the artificial diet containing 10% fish meal and did not differ from those fed the artificial diet containing 10% scallop tissue meal or 20% fish meal (p>0.05). The contributions of different food ingredients calculated with stable isotopes indicated that the contributions of fish meal and scallop tissue meal to the food absorption of sea cucumbers did not show significant difference. Moreover, the contribution of animal protein to the food of sea cucumber did not showed significant increase and the contribution of the sea weed Sargassum thunbergii was elevated with the increasing proportion of animal protein in the diet, suggesting that excessive animal protein inhibited the digestive activities of sea cucumber. The digestive data were consistent with the food contributions revealed by stable isotope. The sea cucumbers fed the diets containing 10% fish meal or scallop tissue meal showed highest proteinase activity and its avtivity decreased with the increasing proportion of animal protein in the diet while the changes in the activities of lipase and amylase did not show significant difference between the different diet groups. The results of the present study suggested that addition of animal protein with the proportion of 10% in the artificial diet of sea cucumber might enhance the growth of sea cucumbers and the scallop tissue meal might be used as substitute ingredient for the artificial diet of sea cucumber.