Colonization and Probiotic Effect of Metschnikowia sp. C14 in the Intestine of Juvenile Sea Cucumber, Apostichopus japonicus

Viable cell count was used to determine whether Metschnikowia sp.C14 can colonize the intestine of juvenile sea cucumber Apostichopus japonicus.Sea cucumber individuals were divided into two groups,which were fed the control diet for 38 days or the C14-supplemented diet at 105 cells g−1 diet for 28 days,then the control diet from day 29 to day 38.The number of C14 cells in the intestine of sea cucumber fed the C14-supplemented diet significantly increased from day 7 to day 28,and decreased from day 29 to day 38.Sea cucumber fed with the diet containing C14 showed a significant increase in trypsin activity and lipase activity from day 21 to day 33 compared with the control.Feeding C14 significantly improved the phagocytic activity and respiratory burst in coelomocytes from day 21 to day 35 and from day 14 to day 38,respectively.In addition,there was an obvious enhancement in lysozyme activity(from day 21 to day 38 or day 33),phenoloxidase activity(from day 21 to day 28)and total nitric oxide synthase activity(from day 14 to day 38)in coelomic fluid supernatant and/or coelomocyte cell lysate supernatant compared with the control.There were significant positive correlations between the number of C14 cells colonizing the intestine and trypsin activity of the intestine,lysozyme activity of the coelomic fluid supernatant and coelomocyte lysate supernatant from sea cucumber.These data suggested that the number of C14 cells should be maintained at 105 cfu(colony-forming units)g−1 intestine material for the maximum benefit.

Comparison of pigment composition and melanin content among white,light-green,dark-green,and purple morphs of sea cucumber,Apostichopus japonicus

Sea cucumber, Apostichopus japonicus（Selenka）, is a commercially important marine species in China. Among the differently colored varieties sold in China, white and purple sea cucumbers have the greatest appeal to consumers. Identification of the pigments that may contribute to the formation of different color morphs of sea cucumbers will provide a scientific basis for improving the cultivability of desirable color morphs. In this study,sea cucumbers were divided into four categories according to their body color： white, light green, dark green, and purple. The pigment composition and contents in the four groups were analyzed by high performance liquid chromatography（HPLC）. The results show that the pigment contents differed significantly among the white, lightgreen, dark-green, and purple sea cucumbers, and there were fewer types of pigments in white sea cucumber than in the other color morphs. The only pigments detected in white sea cucumbers were guanine and pteroic acid.Guanine and pteroic acid are structural colors, and they were also detected in light-green, dark-green, and purple sea cucumbers. Every pigment detected, except for pteroic acid, was present at a higher concentration in purple morphs than in the other color morphs. The biological color pigments melanin, astaxanthin, β-carotene, and lutein were detected in light-green, dark-green, and purple sea cucumbers. While progesterone and lycopene,which are also biological color pigments, were not detected in any of the color morphs. Melanin was the major pigment contributing to body color, and its concentration increased with deepening color of the sea cucumber body. Transmission electron microscopy analyses revealed that white sea cucumbers had the fewest epidermal melanocytes in the body wall, and their melanocytes contained fewer melanosomes as well as non-pigmented pre-melanosomes. Sea cucumbers with deeper body colors contained more melanin granules. In the body wall of dark-green and purple sea cucumbers, melanin granules were secreted out of the cell. The results of this study provide evidence for the main factors responsible for differences in coloration among white, light-green, darkgreen, and purple sea cucumbers, and also provide the foundation for further research on the formation of body color in sea cucumber, A. japonicus.

Effects of different levels of sweet potato in feeds on body composition and digestive enzymes activities of A postichopus japonicas Selenka

The aim of this study was to test the ef fects of including sweet potato tuber and stem powder in feed on the body composition and digestive enzyme activities of the sea cucumber A postichopus japonicas Selenka. Dif ferent proportions of sweet potato tuber and stem powders(from 10% to 50%) were added into compound feeds, which were supplied to A. japonicas during a 60-day experiment. The results showed that the two sweet potato ingredients had different eff ects on the nutrient contents of the sea cucumber body wall. The group supplied with feed containing 20% sweet potato tuber powder(T2) had the highest level of crude protein in body walls(P <0.05), while there were no significant dif ferences in the moisture and ash contents of body walls among the groups(P >0.05). In all the groups fed with powdered sweet potato tubers(T groups), the proportions of glutamic acid and lysine in body walls were higher than those in the control, whereas the proportion of methionine decreased slightly. Diff erent proportions of sweet potato ingredients in compound feeds also af fected digestive enzyme activities in the sea cucumbers. The activities of protease and lipase first increased and then gradually decreased with increasing proportions of sweet potato materials in the feed. The highest protease activity was in the T2 and the group and the highest lipase activity was in the 10% sweet potato stem(S1) group. These results show that feed components can stimulate digestive enzyme activities in sea cucumber, and that the proportions of tubers and stems of sweet potato in feed can be adjusted to improve the digestion and growth of A. japonicas in marine farms.