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In this paper,in comparison with their WSSV-resistant characteristics,35 selective breeding families of the 4th generation and no-selected shrimp of Litopenaeus vannamei were divided into three groups:relatively high resistant families,mid resistant families and susceptible families,with the average survival rates of 24.45%±6.56%,10.70%±1.41% and 2.72%±2.76%,respectively after 103 copies WSSV/g(body weight)infection,which were significantly different among the three groups(P0.01).Injected WSSV of 102,103,104 and 105 copies WSSV/g,the survival rate of the relative high resistant family 12 was 100%,23.3%±3.5%,7.8%±1.9% and 0 %,respectively;and the survival rate of the mid resistant family 7 was 87.7%±3.8%,12.2%±1.9%,0% and 0%,respectively;and the survival rate of the susceptible family 4 was 54.4%±3.8%,2.2%±1.9%,0% and 0%,respectively;and the survival rate of non-selected was 51.1%±5.1%,0%,0% and 0%,respectively.In comparison with mid-resistant family 7,susceptible family 3 and non-selected shrimp,the THC in relatively high resistant family 12 increased by 20.7%(P0.05),36.7%(P0.05)and 34.4%(P0.05)compared with that of the above-mentioned shrimps,respectively after 103 copies WSSV/g(body weight)infection;the PO activities increased by 40.0%(P0.05),76.3%(P0.05)and 63.4%(P0.05)compared with that of the above-mentioned shrimps,respectively;the SOD activities compared with 31.1%(P0.05),58.8%(P0.05)and 32.0%(P0.05)increased by that of the above-mentioned shrimps,respectively;the POD activities compared with 29.64%(P0.05),44.9%(P0.05)and 43.3%(P0.05)increased by that of the above-mentioned shrimp s,respectively;the content of plasma protein compared with 31.2%(P0.05),38.7%(P0.05)and 39.3%(P0.05)increased by that of the above-mentioned shrimps,respectively.However,there were no significant differences of the THC,PO,SOD,POD and content of hemolymph protein among mid-resistant family,susceptible family and non-selected shrimp.After 4 generations of selection,the immune capability of the shrimp from relatively high resistant family was much higher than that of the other groups and non-selected shrimp,with apparent powerful capability of WSSV resistance.These findings would help to direct the future selective breeding of shrimp for WSSV resistance.

After comprehensively studying OSTU method with maximum variance between two classes and the genetic algorithm (GA) principle, an OSTU method based on the self adaptive genetic algorithm (SAGA) is proposed for image segmentation. In this paper, the OSTU method is optimized in the GA based on the encoding, selection, crossover and mutation operations. The experimental results show that by using SAGA method, the efficiency of getting the optimal solutions can be improved, the premature problem can be avoided to a great extent and finally the satisfying solution can be achieved. The image segmentation results show that the OSTU method based on the SAGA is not only quicker in computing speed, but also higher quality in image segmentation. On the basis of the better image segmentation result, the target position in the CCD image can be extracted more accurately in the centroid method.