| Shrimp culture suffered great damage from diseases. Environmentalpollution is one of the main reasons resulted in diseases outbreak.Ammonia nitrogen and nitrite nitrogen are the main pollutions in theculture system. Effeccts of Ammonia nitrogen and nitrite nitrogen on theimmune response of Litopenaeus vannamei and its susceptibility to Vibrioparahemolyticus was systematical studied by means of the accumulativemortality, several enzymes related with immunity. The results show asfollow:The disease known as Acute Hepatopancreatic Necrosis Syndrome(AHPNS) or Early Mortality Syndrome (EMS), which was officiallyreported in China in2009, had over caused large-scale die-offs ofcultivated shrimp in several countries in Asia. A team of researchers at theUniversity of Arizona had identified the causative agent was Vibrioparahaemolyticus, which was a strain of a bacterium commonly found inbrackish coastal waters around the globe. As for V. parahaemolyticus was conditioned pathogen, it is very important to study the toxicity of ammonianitrogen and V. parahaemolyticus on Litopenaeus vannamei. In order toevaluate the effects of total ammonia nitrogen during the outbreak of AcuteHepatopancreas Necrosis Syndrome in Litopenaeus vannamei, thesusceptibility of the shrimp to Vibrio parahaemolyticus, non-specificimmunity and the expression of LvLT mRNA in the hepatopancreas wereexamined. The2.5mg·L-1,5.0mg·L-1,7.5mg·L-1，10.0mg·L-1and thecontrol ammonia nitrogen concentration gradients were designed asammonia stress experiment groups for20days, and then shrimp of the testgroups and the control group was challenged by V. parahaemolyticus. Theresults showed that, the death rate of shrimp after challenge by Vibrioparahaemolyticus showed peak change in6-24h. The accumulativemortality rate of the treatment groups was0,8,12,20and36%respectively in120h. The activities of phenoloxidase (PO) touched bottomin12h in the control,2.5and5.0mg·L-1group, while that in the7.5and10.0mg·L-1group was in24h. The activities of superoxide dismutase (SOD)increased at first and then gradually declined. So was the activity oflysozyme (LSZ) as well. The expression level of LvLT mRNA in thehepatopancreas of all groups increased in6h and it was high significantlyin the control,2.5,5.0and7.5mg·L-1group than that in the10.0mg·L-1group. It reached its climax at12h, and then it declined gradually in24h. The results indicated that high ammonia nitrogen could cause the inhibitionof immunity of Litopenaeus vannamei, and enhanced the susceptibility of V.parahaemolyticu, and made the mortality increase. Thus, it is so importantto regulate the concentration of total ammonia nitrogen in aquaticenvironment as to prevent the break out of Acute Hepatopancreas NecrosisSyndrome.As for V. parahaemolyticus was conditioned pathogen, it is veryimportant to study the toxicity of nitrite nitrogen and V. parahaemolyticuson Litopenaeus vannamei. The experiment, including the susceptible test ofLitopenaeus vannamei exposed to Vibrio parahaemolyticus and the test oneffect of immune-related enzymes (glutamic-pyruvic transaminase, ALT;glutamic oxalacetic transaminase, AST; alkaline phosphates, ALP;lysozyme, LSZ) to shrimp under different nitrite nitrogen, was carried outto reveal the relationship between nitrite and its stress effect on thesusceptible to shrimp and the immunity to shrimp exposed to Vibrioparahaemolyticus. The2.0,4.0,6.0,10.0mg·L-1were designed as nitritestress experiment groups. Stress experiments last20days, and then shrimpof the test groups and the control group was challenged by V.parahaemolyticus. The results showed that, the dying shrimp was anorecticand the hepatopancreas of deceased shrimp was pale to white and atrophy.The accumulative mortality grew to the peak in48h, and they were0,4%, 8%,16%and24%respectively. The activities of ALT in the control,2.0,4.0mg·L-1groups increased, and then decreased, while that in the6.0and10.0mg·L-1groups kept rising. The activity of AST in the control and2.0mg·L-1groups increased, and then decreased while that in the4.0,6.0and10.0mg·L-1groups kept rising. In the control,2.0and4.0mg·L-1groups,the activity of ALP increased, and then recovered to normal level white thatin6.0and10.0mg·L-1groups continued to slowdown. The activity of LSZin the control group at different point of time had significantly higher thanthat of6.0and10.0mg·L-1group. The results indicated that high nitritenitrogen could cause the inhibition of immunity of Litopenaeus vannamei,and then enhanced the susceptibility of V. parahaemolyticus, and makemortality increase. Thus, it is so important to regulate the concentration ofnitrite nitrogen in aquatic environment as to prevent the break out of AcuteHepatopancreatic Necrosis Syndrome.To investigate the effectiveness of bio-floc technology to degradeammonia nitrogen and nitrite nitrogen and growth performance of shrimpin different stocking density, the fermentation solution of Wheat bran, canesugar and Bacillus substilis was added to the water of indoor industrialculturing of Penaeus vannamei. Results showed that: The levels of pHvalue, ammonia and nitrite were lower and stable in the ponds of the trialgroup than that of the control. In the last period, the number of species of protozoa and rotifers were the majority in the ponds of the trial group. Theammonia excretion rates of the three treatments were increased respectivelyby25.8%,9.7%and19.3%than that of the control group. The averageyield of shrimp of the trial group was respectively (2.05±0.13) kg·m-2,(2.07±0.27) kg·m-2and (1.98±0.32) kg·m-2while that of the control groupwas (1.49±0.09) kg·m-2. The results indicated that bacillus substilis couldimprove the water quality, the anti-disease ability and yield of Penaeusvannmei. |
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