Study On The Poly-culture Technique Of The Crab Portunus Trituberculatus

In the thesis, the poly-culture of the crab Portunus trituberculatus with the shrimps Fenneropenaeus chinensis and Litopenaeus vannamei was conducted using land-based enclosures, respectively. The growth of the crab and the shrimps, changes of physiochemical parameters of seawater and sediments in the enclosures were determined. The optimal culture ratio of P. trituberculatus to F. chinensis or L. vannamei was further discussed according to the poly-culture efficiency. Details on three main studies of the thesis were as follows:1. Study on the poly-culture for the crab Portunus trituberculatus and the shrimp Fenneropenaeus chinensisIn the study, the poly-culture was conducted in the land-based enclosure (5×5 m), in which 9 ind·m^-2 of F. chinensis and each of four different densities of P. trituberculatus, i.e., 0, 3, 6, 9 ind·m^-2 were cultured. In the late culture period, the salinity and temperature decreased drastically, whereas the concentration of TAN, NO2-N and NO3-N increased sharply because of the effect of Typhoon"Wei pa". These changes of culture seawater parameters in turn led to the death of a large number of the crabs and shrimps. No significant difference was detected in the final size, survival rate and net production of the shrimp in all the treatments. In contrast, positive relationship was found between the net production of the crab and its culture density. This study indicated that the poly-culture of 9 ind·m^-2 each of P. trituberculatus and F. chinensis did not reach the maximum carrying capacity under this culture environment.2. Study on the poly-culture for the crab Portunus trituberculatus and the shrimp Litopenaeus vannamei2.1 Study on the effects of poly-culture for crab with different density of shrimp There were eighteen enclosure(5×5 m) where P. trituberculatus was cultured at a density of 6 ind·m^-2 and L. vannamei was cultured in six different densities were 0, 15, 45, 75, 105, 135 ind·m^-2 respectively. The results showed that all the poly-culture treatments were superior to the crab mono-culture treatment in survival rate, final size and net production. The highest survival rate, final size and net production of shrimp were 45.71%, 43.22g·ind-1 and 1191kg·hm^-2 for the treatment of 45ind·m^-2, which followed by 44.58%, 39.13g·ind-1, 1050 kg·hm^-2 for the treatment of 75ind·m^-2, and the lowest was 35.13%, 32.87 g·ind-1, 693 kg·hm^-2 occurred in crab mono-culture treatment during the experimental duration of 60 d. The final size and survival rate have negative correlation to their stocking density. The concentration of TAN, NO2-N, NO3-N and TN in poly-culture was higher than those in crab mono-culture significantly, and the concentration of those was increased with the shrimp stock density significantly at the end of culture period. The concentration of TAN in all poly-culture treatment was above 500 ug·L-1 after 50 d. Therefore, the optimal density for this poly-culture was 6 ind·m^-2 crab (crab biomass 0.144 g/m²) and 45～75 ind·m^-2 shrimp (shrimp biomass 0.536～0.893 g/m²), respectively.2.2 Study on the effects of poly-culture for shrimp with different density of crabThere were fifteen enclosure (5×5 m) where L. vanname was cultured at a density of 45 ind·m^-2 and P. trituberculatus was cultured in six different densities were 0, 3, 6, 9, 12 ind·m^-2 respectively. The results showed that the poly-culture treatments of 3 ind·m^-2 and 6 ind·m^-2 were superior to crab mono-culture treatment in survival rate, final size and net production. The poly-culture treatments of 9 ind·m^-2 and 12 ind·m^-2 were inferior to crab mono-culture treatment in survival rate, final size and net production. The final size and survival rate have negative correlation to their stocking density. The concentration of TAN, NO2-N, NO3-N and TN in poly-culture was higher than those in shrimp mono-culture significantly, and the concentration of those was increased with the crab stock density significantly at the end of culture period. The concentration of TAN in all treatment was above 500 ug·L^-1after 50 d. The treatment given the best culturing benefit was considered as shrimp 45 ind·m^-2(shrimp biomass 0.536 g·m^-2) and crab 36 ind·m^-2(crab biomass 0.072～0.144 g·m^-2).2.3 Study on the effects of poly-culture for Portunus trituberculatus with Litopenaeus vanname on sediment quality TOC, TC, TN and TP in the enclosure sediments were investigated during the poly-culture period. No sharp changes were detected in TOC and slow accumulation in TP. Significant decrease was found in TC and obviously rapid accumulation in TN, indicating the obvious decrease of the ratio TC to TN. Results also showed that the values of TP, TN and comprehensive contamination index were higher in the treatments containing 105 and 135 ind·m^-2 shrimp than those in the other treatments. Similarly, values of the above parameters were also higher in the treatments containing 9 and 12 ind·m^-2 crab than those in the other treatments. Therefore, the optimal poly-culture density of P. trituberculatus and L. vanname was 6 ind·m^-2 and 0～75 ind·m^-2 in the study 2.1. Regarding the study 2.2, the optimal poly-culture density of L. vanname and P. trituberculatus was 45 ind·m^-2 and 0～6 ind·m^-2, respectively.3. Study on different feeding technique of poly-culture for Portunus trituberculatus with Litopenaeus vannameIn this study, the poly-culture densities of P. trituberculatus and L. vanname were conducted as 0.5 ind·m^-2 and 36 ind·m^-2, respectively. The controls only fed shrimp diet was set as SF100%, and those only fed crab diet CF100%. The treatments were fed 50% shrimp diet and 50% crab diet (SF50%CF50%). After 50 d, the highest survival rate, final size and net production of shrimp were determined in SF100%, followed by SF50%CF50%. Whereas, the lowest values of these parameters were found in CF100%. On the other hand, the order of survival rate, final size and net production of crab in the controls and treatments was CF100%>SF50%CF50%> SF100%, which showed a positive correlation with the feeding ration. The study demonstrated that the mixing feeding in the poly-culture of crab and shrimp could raise their growth and survival rate. However, study on the optimal proportion of the mixing feeding need be further done.