Characteristics Of Cyanobacterial Community And The Effect Of Microcystins On Activity Of Immune-related Enzymes In The White Shrimp Litopenaeus Vannamei

During the middle and later periods of farming in low salinity shrimp pond, with imput of a mass of feed, organic pollution and eutrofication may gradually appear and lead to cyanobacterial bloom, which can produce microcystins to influence the growth of shrimp. The relationship among cyanobacteria quantity, water quality factors and cyanobacterial toxins, and the effect of microcystins(WC-LR) on activity and gene expression of immune-related antioxidant enzymes in the white shrimp Litopenaeus Vannamei was investigated by field survey and toxicity experiments. The main results are as follows:By sampling continuously from shrimp ponds, we found that the main cyanobacteria in the shrimp pond were Spirulina subsalsa, Anabaena circinalis, Oscillatoria chlorine, Microcystis aeruginosa and so on, and the dominance of Spirulina subsalsa was 0.53~0.73. Cyanobacteria became dominant species in the water body, accounted 88%~99% of microalgae quantity. Cyanobacteria quantity ranged from 1.03xl09-4.76xl09 ind/L, biomass from 0.99×109~5.89×l09 cell/L, Shannon-Wiener index of microalgae ranged from 1.16 ~ 2.49, the state of shrimp pond was moderate pollution. The concentration of DIN, PO4--P and COD were 0.13~2.30mg/L, 0.25~2.39mg/L and 1.94~13.79mg/L, respectively. The concentration of microcystins was 0.18μg/L ~0.79μg/L. According to the results of multiple regression analysis, cyanobacteria quantities was positively correlated with COD.The results indicated that low-salinity eutrophicatived water body is beneficial for the growth of cyanobacteria,which made it become the dominant species in microalgae community.Different concentrations of nitrogen, phosphorus and ratio of N/P were seted to determine the effects of on the growth and microcystin production of Oscillatoria sp. We found that different concentrations of nitrogen, phosphorus experiment, the quanlities of algae cells, the intake ratio of nitrogen dissolved in the water, chla content, phycobiliproteins content and microcystin production were increased when the concentration of nitrogen ≥ 15.0mg/L. In Different concentrations of phosphorus experiment, the quanlities of algae cells, the intake ratio of nitrogen dissolved in the water, chla content and phycobiliproteins content were increased when the concentration of phosphorus ≥15.0mg/L while microcystin production was decreased. In different ratio of N/P experiment, the quanlities of algae cells, the intake ratio of nitrogen dissolved in the water, chla content, phycobiliproteins content and microcystin production were increased when the ratio of N/P ≥15:1. The results indicated that variation of nutritive salt and ratio of N/P have significant effects on the growth and microcystin production of Oscillatoria sp.In the acute toxicity experiment, by injecting MC-LR into the body, the activities of superoxide dismutase, glutathione peroxidase, peroxidase,acid phosphatase,alkaline phosphatase and lysozyme in the hepatopancreas of Litopenaeus Vannamei were significantly affected by MC-LR with the increasing of time(P <0.05). Activities of these emzymes increased in the early period of the experiment and decreased in the later period. The activities of superoxide dismutase,glutathione peroxidase and peroxidase increased 15.62%, 18.76% and 32.86% at 4h compared with the control group, reapectively. The peak values were 123.08U/mg, 59.62U/mg and 29.95U/mg, reapectively. The activities of acid phosphatase and alkaline phosphatase increased 25.02% and 37.99% at 2h compared with the control group,reapectively. The peak values were 181.76U/mg and 157.90U/mg, reapectively. The activity of lysozyme increased 33.57% at 8h compared with the control group. The peak values was 28.80U/mg. The results indicated that high dose MC-LR can significantly suppress the activities of immune-related enzymes in Litopenaeus Vannamei.In the sub-chronic toxicity experiment, by releasing different concentrations of MC-LR into water, the activities of superoxide dismutase, glutathione peroxidase, peroxidase,acid phosphatase,alkaline phosphatase and lysozyme in the hepatopancreas of Litopenaeus Vannamei were significantly affected by MC-LR after 30 days(P <0.05). With the increasing concentration of WC-LR, the activities of superoxide dismutase, glutathione peroxidase and peroxidase reach their peak values at concentration of 3.0μg/L, 250.40U/mg、 125.11U/mg and 7.42U/mg, reapectively. Activities of acid phosphatase and alkaline phosphatase inereased under the concentration of 0.72μg/L and decreased after that. The peak values were 76.97 U/mg and 91.56 U/mg. The activities of lysozyme reach their minimum value at concentration of 1.47μg/L with the increasing concentration of WC-LR, The peak values was 9.69U/mg. With the increasing concentration of WC-LR, the gene expression level of superoxide dismutase and glutathione peroxidase up-regulated while the gene expression level of lysozyme down-regulated significantly, which was consistant with the variation of activities of their enzymes. The results indicated that low concentration MC-LR dissolved in the water can cause stress response in Litopenaeus Vannamei in the long term, and Litopenaeus Vannamei can regulate the activities and gene expression of immune-related enzymes to cope with stimulation of MC-LR.The results above all indicated that low-salinity eutrophicatived water body is beneficial for the growth of cyanobacteria, which cause deterioration of water body. Variation of nutritive salt and ratio of N/P have significant effects on the growth and microcystin production of Oscillatoria sp. Acute and chronic exposure of MC-LR to Litopenaeus Vannamei can induce the variation of activities of immune-related enzymes and weaken the immunity of it.