| 1. How to eliminate negative effects of sea mud in feed for juvenile sea cucumber (Apostichopus japonicus) is an unsolved problem. Here we propose a method that using stable carbon isotope ratio to prove possibilities of replacement for sea mud with yellow soil. The results showed that feeding juveniles with algae contained 20% yellow soil and sea mud at 7.5% their body weights and for 60 days, the SGR of A. japonicus were (1.95±0.13)%, (1.72±0.17)%, contributions of yellow soil and sea mud to food sources of juveniles were (9.78±1.37)% and (9.89±1.47)%, contributions of green algae to food sources of juveniles were(90.22±1.37)% and (90.11±1.47)%, there was no significant difference for the same index between treatments of sea mud with yellow soil(P>0.05). These results support replacing sea mud with yellow soil is of great feasibility and can save costs and minimize the disturbance of Shallow sea beds.2. By analysing stable carbon isotopic values (δ13C values) of the organisms collected in a sea cucumber farming pond, it is found that the 813C values of one animal has a close relation with that of the digested food and may be useful in elucidating their food sources. Using the stable carbon isotopic tracers may help confirm the importances and compositions of food source for filter feeders and predators. The investigations show that the main food sources of the Apostichopus japonicus can be divided into three groups in terms of stable carbon isotopic composition:benthic diatoms, meiofauna and organic matter in sediments (POM and SOM).The results lead to a conclusion that theδ13C value is useful tracer to investigate the food web structure of coastal ponds.3. Stable carbon isotope ratios (δ13C) were used to estimate the contribution of supplemental feed to growth of juvenile sea cucumber cultured in pond enclosures. Five different culture densities (5,10,15,25 and 35 individuals /m2) of sea cucumbers were cultured in pond enclosures for 60 days, keeping constant feeding ration of 5% initial weight. The results were as followed:1) supplemental feed had significant effects on final weights of sea cucumbers both in aquarium and enclosure study(F=148.541, P=0.003; F=6.301, P=0.018, final weights sea cucumbers fed on supplemental feed were higher than that in unfed enclosures, significant differences were observed among different densities (F=13.009, P<0.01), a decrease in final weight with increasing stocking density was described.2) Supplemental feed had significant effects onδ13C values of sea cucumbers in aquariums, Supplemental feed, density had significant effects onδ13C values of sea cucumbers in aquariums, Supplemental feed, and density had significant interaction onδ13C values of sea cucumbers in aquariums. Theδ13C values of sea cucumbers fed on supplemental feed showed a descending trend, ranged from (-13.262±0.183)‰to (-15.102±0.189)‰, as the density increased from 5 to 35 inds./m2. It was calculated that a higher contribution of supplemental feed to sea cucumber growth was favored when density was increased, reaching a minimum (3.78±2.98)% at 5 inds./m2 and a maximum (29.48±3.31)% under the highest stocking condition.The contributions of supplemental feed showed significant differences among different densities (F=24.439, P<0.01). Food limitation may account for a fact of lower final weights while higher feed contributions were obtained under high density conditions.Results from this work should be an aid to developing intensive culture and optimum feed for holothurians.4. Food sources of sea cucumber cultured in a bottom-renovated pond were determined using stable carbon and nitrogen isotope biomarkers. Based on computing result of the IsoSource software, Apostichopus japonicus's diet consisted of bacteria(13%～34%), sediments(4%～40%), diatoms(0～41%), macroalgae(0～52%), and meiofauna(0%～49%). Playing a primary role in the feeding of sea cucumber, bacteria contributed average 26.6% possible food sources, sort by size, contributions of sediments, macroalgae, meiofauna and diatom were 21.5%,19.1%,18%,14.8%, respectively.5. Food contribution of stones, tiles, plasic pipes, hollow bricks and cement pipes to cultured sea cucumber (Apostichopus japonicus a) in enclosures were determined using stable carbon isotope biomarker.The surface organic matter of five settlement substrata consisted of diatoms, sediments, bacteria and bacteria. Playing a primary role in the surface organic matter, diatom contributed verage 39.9%～73% possible food sources, sort by size, contribution of sediments and bacteria were 17.3%～34.5% and 9.7%～29.6%, respectively. Contributions of the surface organic matter of five settlement substrata ranged from none to 5%, average 14.5%～32.6%. Contribution ranked highest to lowest is plasic pipes, hollow bricks, cement pipes, tiles and stones. Our results would be helpful in the choosing of more appropriate settlement substrata for cultured holothurians.6. Growth, survival and food sources of sea cucumber(Apostichopus japonicus) co-cultured with scallop(Chlamys Farreri) in Ponds were determined using stable carbon isotope biomarker. The results showed the specific growth rate (SGRw) and survival rate(SR)of A japonicus were (1.43±0.72)% and (96.67±5.77)% that both were higher than monoculture holothurians, (1.29±0.62)%d-1 and (93.3±5.77)%, respectively. Contribution of food sources of monoculture sea cucumber ranked highest to lowest was microalgae, bacteria and sediment and their contributon was 62%,20.6% and 17.4%, while co-cultured ones were microalgae, bacteria, sediment, scallop biodeposits and their contributon was 51.9%,22%,15.8% and 10.3%. Results here would be of some help in the choosing of appropriate cocultued aquatic aquatic organism for holothurians.
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