Integrated Multi-trophic Aquaculture(IMTA)system And Mutually Beneficial Effects Of Apostichopus Japonicus And Styela Clava

Pond farming is the main production mode of Apostichopus japonicus in north China,the long-term high-density culture has impacted the quality of aquatic environment and decreased yield of A.japonicus.How to carry out ecological aquaculture,making full use of nutrient elements in ponds and improving the utilization rate of nutrient elements,is an urgent problem to be solved.In this study,an integrated multi-trophic aquaculture(IMTA)system utilizing A.japonicus and Styela clava was constructed to verify the feasibility of the integrated culture of A.japonicu.s and S.clava.The mutually beneficial effects between organism and environment of the integrated culture system was expounded from two aspects of environment factors and animal physiology.The main results are as follows:1.Construction of the integrated system of A.japonicus-S.clavaS.clava can filter the microalgae and organic matter in the water and converts them into baits of A.japonicus by excretion,which can effectively improve the utilization rate of nutrient elements.In the indoor simulated breeding experiments,S.clava was suspended from the nylon rope in the water tanks,A.japonicus was placed at the bottom,maintaining a certain density of microalgae.We established different specifications of animal and microalgae co-culture groups and A.japonicus and S.clava integrated groups.Results showed that there was no significant difference between different specifications of animal groups under the same culture mode.The concentrations of nutrients in water and sediments of the integrated groups were remarkably lower than those of the A.japonicus monoculture groups,close to those of the animal and microalgae co-culture groups.So was the number of bacteria on the attachment.A.japonicas grew best in the integrated groups.The test of optimization showed that no significant difference was detected between groups cultured with different microalgae densities.Higher levels of ascidian biomass(800 g wet weight/m3)increased specific growth rate(SGR)of A.japonicus while reducing the coefficient of variation(CV)of large(L)A.japonicus and increasing that of small(S)A.japonicus.An increasing number of L A.japonicus in groups led to decline of SGRs and increase of CVs for all size A.japonicas.Thus,the optimal condition for IMTA system was determined as microalga density of 5×102 cell/mL,ascidian biomass of 800 g wet weight/m3,with L A.japonicus 5-6 ind/m2 and S A.japonicus 12-1 5 ind/m2.2.Studies on mutually beneficial mechanism of the integrated systemAccording to the optimized parameters,4 test groups were set up:mixculture groups(feeding/non-feeding)and integrated groups(feeding/non-feeding).Tank cultivation trials in laboratory showed that the water quality of the integrated groups maintained at the first/second class of the Chinese national standard and the concentrations of various forms of nitrogen and phosphorus in water and sediments were significantly higher than those of mixculture groups.The composite indices of environment,nutrient and living for A.japonicus in the integrated culture system were all higher than those in the mixculture system under the same feeding mode.Results showed no correlation between the environment composite indices and SGR of L,Sb,Ss A.japonicas and highly positive correlation between the nutrient and living composite indices and SGR of L,Sb,Ss A.japonicas.The mutually beneficial mechanism of the IMTA system of A.japonicus-S.clava was realized mainly through the means of nutrition mutual benefit.The physiological of L and Sb A.japonicus little changed.Activities of hexokinase,pyruvate kinase,lactic dehydrogenase,adenosine triphosphatase of Ss A.japonicus in the IMTA system rised 8.8%,10.5%,5.2%,18.7%respectively than those in the mixculture system;additionally,their digestive enzymes rised 6%-10%.In general,the integrated system has a positive effect on physiological metabolism of A.japonicus.3.The practice of integrated system in a pondThe 4 groups above-mentioned were tested in a pond for 1 year.The contents of different forms of N and P in water and sediments remained at low levels and varied closely related to seasons.The concentrations of ammonia nitrogen(NH4+-N),nitrite nitrogen(NO2--N),nitrate nitrogen(NO3--N)and total nitrogen(TN)in the integrated groups were 16.2%,1.2%,5.5%,6.8%respectively higher than those in the mixculture groups under the same feeding mode.A.japonicus in the IMTA system grew better than the corresponding ones in the A.japonicus mixculture system,showing no significant difference on survival rates and biochemical composition.In conclusion,the integrated culture system can improve the environmental factors,nutritional factors and living factors and enhance the physiological metabolism of A.japonicus to promote the growth and aquaculture effect of A.japonicus,increasing economic benefits and ecological effects.