| Sea cucumber aquaculture has become the specific mariculture industry of China, while it has been facing huge challenge, for example, antibiotic issue and disorderly uses, with its quick development. These problems has potential threat on the environment and food safety. Therefore, how to realize containable development of aquaculture modes is a critical way for sea cucumber aquaculture industry, which also need high output and quality of seedling. During the larval rearing the diet is crucial, for larval survival and memorphosis rates are low. Also, the period for juvenile culture is very long and how to realize effective and clean aquaculture is the bottleneck of breeding hatcheries. This research was aimed to demonstrate the effects of vegetable diet and animal diet on the larval growth, physiology and water quality, and the utilization effects of biofloc technique on juvenile cultivation. Moreover, we aimed to supply theoretical basis for environmentally friendly breeding and cultivation, and development relevant aquaculture techniques. The main results were as follows:1. the effects of different diets on larval growth physiology, metamorphosis,, survival and water quality factorsVegetable diet (seagrass mashed solution) and animal diet (mainly marine red yeast) were used for the tests. Three groups were set, i.e., I was seagrass mashed solution, II mainly marine red yeast and III half of seagrass solution and half of red yeast, individually. The larval growth physiology, metamorphosis, survival and water quality factors were determined. Results showed that 1) larval growth was fast in mixed diet group compared to the other two and finished metamorphosis 24 h earlier.2) the activities of proteinase, amylase, SOD increased with the larval growth stages in these three groups, of which activities of SOD in II and III groups were significantly higher than those of I group. The activities of CAT in I and II group also had increasing trend, whereas those of III did not change obviously. The activities of AKP were higher during the late larval stage in all the three groups, whereas ACP had no obvious change.3) larval metamorphosis rates of I group after 48 h,72 h and 15 d were significantly lower than the other two.4) The ammonia and nitrite concentrations increased during the culture period, while ammonia concentrations in I group were the highest and nitrite concentrations in III group were the highest. From the above results, the digestive enzyme activities showed that mixed diet was beneficial to larval digest and immuno-enzyme activities showed that vegetable diet was beneficial to larval immune system. Larval metamorphosis rates and juvenile survival rates showed that mixed diet was better than vegetable and animal diets. Conclusively, mixed diet was better than vegetable diet and animal diet was the worst based on all the factors.2. The isolation and identification of effective microorganisms for ammonia and nitrite degradationIsolation and identification the bacteria in sediment environment of sea cucumber cofferdam aquaculture sea. Screened three strains degradating ammonia and nitrite (NO. S721? S722?S729), through 30? shaking culture 7 d, added 5%(NH4) 2SO4 solution 1 mL every day; By accessing 5 percent three bacterial suspension in 300 mL sea cucumber seedling breeding late, through 30?,160 r/min shaking culture 7 d, determined ammonia, and nitrite levels every 2 days, screened high degradation efficiency of ammonia and nitrite strain strains S729. After 16S rRNA sequencing, matching degree is 100% with Bacillus subtilis. S729 can be degradate the ammonia from initial concentration of 2.20 mg/L to the concentration 1.08 mg/L degradate the nitrite from initial concentration of 0.88 mg/L to the concentration 0.61 mg/L within 10 days. the sixth day have been as low as 0.51 mg/L, by detecting the degradation of ammonia and nitrite of the strain. The results show that the strain has efficient degradation of ammonia and nitrite effects to the aquaculture waters.3. Biofloc formation by adding S729 and appropriate carbon and its effect on juvenile growth physiology, survival rate and water qualityThe molasses were used as carbon source. Three groups were set, i.e., A group, the blank control, B group,5% of diet quantity for molasses addition and 104 CFU/mL S729, C group, 10% of diet quantity for molasses addition and 104 CFU/mL S729. For blank control, the cultivation seawater was changed once per 10 days, and that in the experimental groups was changed once per 20 days. After 60 days cultivation, results showed that 1) juvenile weight of blank control was higher, better than that of C group and that of B group was the lowest, whereas SGR and FCR in A and C were no different and those of B was the lowest. The survival rates in the three groups had no different.2) the digestive enzyme activities showed that proteinase and lipase decreased first and then increased, while amylase increased during the period. The digestive enzyme activities in the experimental groups were significantly higher than those of the blank control.3) the immumo-enzyme activities showed that SOD. lysozyme. PO activities increased gradually and SOD activities decreased first and then increased. On the whole, the immumo-enzyme activities of C group were higher.4) the total cultural bacterial number was significantly higher in experimental groups than that of blank control with the addition of S729 and carbon source. The vibrio number in the three groups was on the level of 104 CFU/mL, while that in experimental groups was lower than that in blank control. The bacillus densities in the experimental groups increased with the period and were one order of magnitude higher than those in blank control.5) The ammonia and nitrite concentrations in B and C groups were lower than those in A during the whole period, while COD in those higher than A group. The above results showed that using biofloc technique could delay the water change by one round and had no adverse effect on juvenile growth. The digestive enzyme and immuno-enzyme activities were higher than those in blank control on the whole. Also, the biofloc technique could regulate the ammonia and nitrite concentrations of the cultivation seawater and inhibit the vibrio growth to a certain content. Conclusively, biofloc technique can realize the highly effective and clean aquaculture of sea cucumber, and decrease the effluent contamination. Moreover, biofloc technique can avoid chemical and antibiotic usage to realize the green, healthy and containable aquaculture. |
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