| Microcystins (MC) are cyclic heptapetide hepatotoxins produced mainly by freshwater cyanobacteria, which can lead to illnesses and mortality in wild and domestic animals, as well as in humans. Due to its accumulation in aquaculture animals, it has caused great attention. The distribution and dynamics of microcystin-LR in various organs of the Tilapia through three different exposure routes (intraperitoneal injection,bath immersion, oral ingestion) were studied in this paper.Determination of microcystins in fish tissue using High Performance Liquid Chromatography was developed through optimization of extration, chromatographic conditions and solid phase extraction. Results showed that the recovery of muscle, liver, plasma, gallbladder, intestine,gills were76.1%,74.9%,79.4%,73.0%,68.4%,76.7%respec-tively. The average recovery was74.8%, R.S.D was<10.5%.The detection and quanti--fication limits were20μg/kg.The method was applied to MC-LR detection, and good results were observed.Fish were injected i.p. with pure MC-LR at a dose of250μg/kg BW. Quantitative and qualitative determinations of MC-LR in liver, plasma, gallbladder, gill, intestine, muscle were conducted by HPLC at2h,12h,24h,36h,48h after injection.The results showed that MC-LR could accumulate in the various tissues of Tilapia. Liver as the target organ had the highest accumulation, its concentration reached the maximum at24h (4.938μg/g), followed by a sharp decline afterwards. The maximum MC-LR in plasma and gallbladder were0.390μg/ml and0.285μg/g, occurring at2h and24h respectively. A little MC-LR was detected in the intestine and gill. Redistribution of MC-LR to those tissues is the second mechanism besides the desorption from the blood stream.No detectable MC-LR was found in muscle in this experiment.The accumulation and depuration of microcystin-LR in Tilapia under bath immersion condition was investigated in this experiment.In accumulation period, fish were exposed at two concentrations (62.5μg/L and1.39μg/L) of dissolved MC-LR in water at1d,3d,8d,15d. Then the depurations of the accumulation fish were observed.Quantitative and qualitative determinations of MC-LR in liver, gill, intestine, muscle and gallbladder were conducted by HPLC.Results showed the existence of MC-LR in liver, gill, intestine, muscle under high concentration, while no detectable toxin were found at low concentration.MC-LR uptake might occur at two different organs:intestine and gills, through either feeding (including drinking) or respiratory activities. The liver showed the major bioaccumulation, and it reached its maximum (2.036μg/g) at8d in accumulation period. Extremely low levels of MC-LR were found in the fish flesh.The present study indicated that the average concentration of MC-LR in flesh was only2.7%of livers at accumulation period, and at deputation period, it was8.9%.Though no MC-LR was detected in gallbladder, the existence of MC-LR in intestine indicated its important role in the toxin metabolism.A subchronic toxicity experiment was conducted to examine tissue distribution and depuration of microcystin-LR in in tilapia fish during a course of44days. Two groups (1,2) were used, and in group1, the fish were fed naturally with fresh Microcystis viridis cells (collected from a entropic pond) throughout the experiment, while in group2, the food of the fish were M. viridis cells previously disrupted (to simulate a senescent bloom).The accumulation experiment were consistent for24days and then changed to artificial fish food for depuration. HPLC was used to measure MC-LR and MC-RR in the M. viridis cells, the liver and muscle tissue of tilapia. MC-LR and MC-RR in the collected Microcystis cells varied between6.3～49.2μg/L and25.8～532.2μg/L respectively. The results showed that the tilapia was able to accumulate MC-LR through feeding toxic cells. The cells-disrupted group (group2) showed high accumulation rate than non-disrupted group (group1).The maximum MC-LR in the liver and muscle of the fish in group1were1.856μg/g and0.036μg/g, respectively. While in group2, it were2.021μg/g and0.071μg/g.During the accumulation period, the average MC-LR concentration of liver and muscle in group1was1.029μg/g and0.028μg/g, lower than the group2(1.171μg/g and0.051μg/g).The depuration of MC-LR in tilapia were observed in the following20days, and liver showed high depuration rate than muscle. The grazing ability of tilapia on toxic cyanobacteria suggests an applicability of using phytoplanktivorous fish to counteract cyanotoxin contamination in entropic waters. |
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