In the experiment ,the influence of different concentrations of Cr6+ (120 .00 ,160 .80 ,215 .47 , 288 .73 ,and 386 .90 mg/L) on histological structure of brain and hepatopancreas and superoxide dismutase (SOD) activity in hepatopancreas were studied in grass carp (Ctenopharyngodon idellus ) with body weight of some 10 g at water temperature of (20 ± 1) ℃ by a hydrostatic test to seek for the accumulation and toxicity mechanism of heavy metal .It was found that the LC50 of Cr6+ to grass carp was 302 .77 mg/L in 24 h ,154 .47 mg/L in 48 h ,and 78 .89 mg/L in 96 h ,with safe concentration of 12 .068 mg/L calculated by formula(48 h LC50 × 0 .3)/(24 h LC50/48 h LC50 )2 and 7 .489 mg/L estimated by formula 96 h LC50 × 0 .1 .In the early stage of Cr6+ poisoning ,the grass carp exposed to Cr6+ had clustered hepatopancreas cells with slightly enlarged nuclei and the slightly exhibited cytoplasm .As the time elapsed ,the significantly aggregated hepatopancreatic cells showed obvious hypertrophy and disorder discrete .The nucleus was rel‐atively narrow in shape ,and the cavitation .The brain cells were found to be expansion ,discrete ,nuclear reduction ,a slight overflow of the cytoplasm ,a small number of brain cell cytoplasm overflow ,and resid‐ual nuclear material scattered distribution in the grass carp exposed to Cr 6+ ,thus leading to hepatopancre‐atic cell necrosis .With the increase in Cr6+ concentration and time ,the activity of SOD was decreased in the hepatopanceas of grass carp .%在水温（20±1）℃下，采用静水测试法研究水体中不同质量浓度 C r6＋（120．00、160．80、215．47、288．73、386．90 mg／L ，重铬酸钠配制）对体质量约10 g草鱼脑和肝胰脏的组织结构及肝胰脏中超氧化物歧化酶活性的影响，以探讨重金属的毒性积累和毒性机制。试验结果表明，C r6＋对草鱼的24、48、96 h半数致死质量浓度（LC50）分别为302．77、154．47、78．89 mg／L ，由（48 h LC50×0．3）／（24 h LC50／48 h LC50）2和96 h LC50×0．1计算出安全质量浓度分别为12．068 mg／L和7．489 mg／L。中毒初期肝细胞轻微肥大，无序离散，细胞核相对缩小，胞浆轻微展出；随着时间的延长，肝胰脏异常的程度更加严重，甚至肝坏死，肝细胞明显肥大，无序性离散程度明显增大，细胞核明显缩小，肝细胞胞浆展出，细胞空化；脑细胞开始出现破裂，细胞液溢出，细胞核轻微聚集；随后脑细胞的异常程度更加严重，细胞破裂、细胞核聚集程度严重。随着C r6＋质量浓度的升高和时间的延长，草鱼肝胰脏中超氧化物歧化酶活性降低。
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