Abstract
The acute toxicity of divalent mercury ion to Anguilla japonica from seawater and freshwater aquaculture was assessed. In particular, the effects of toxicity on the microstructures of the gill and liver tissues were examined using the hydrostatic method, without feeding, at a water temperature of 20 °C. The median lethal concentrations (LC50) of divalent mercury ion to fishes in seawater and freshwater over various durations were: 24 h = 1.637 and 1.428 mg/L; 48 h = 1.562 and 1.377 mg/L; 72 h = 1.530 and 1.284 mg/L; and 96 h = 1.442 and 1.228 mg/L. The safety mass concentrations were 0.1442 and 0.01228 mg/L, respectively. After exposure to divalent mercury ion, adhesion between the gill lamellae and massive cellular disintegration and necrotic shedding were observed in the gill tissue sections. The liver tissues underwent hyperemia and swelling, with the appearance of blood spots, swelling of the hepatocyte mitochondria, dilation of the rough endoplasmic reticulum, and intercellular inflation.
Highlights
Rapid industrial and agricultural development, increased urban population size, and improvements to people’s living standards have caused large amounts of wastewater containing heavy metals to flow into rivers, lakes, and oceans
The reactions of A. japonica to mercury in the two types of aquaculture were basically similar under the same conditions
Toxicity and Median Lethal and Safety Concentrations of Divalent Mercury Ion to Anguilla japonica liver tissue structures were observed in fishes from the control group
Summary
Rapid industrial and agricultural development, increased urban population size, and improvements to people’s living standards have caused large amounts of wastewater containing heavy metals to flow into rivers, lakes, and oceans. The pollution sources of heavy metals include volcanic activity, rock weathering, soil erosion and other natural factors, as well as anthropogenic factors such as train flue gas discharge, sewage irrigation, construction engineering, metal products manufacturing, mining, incineration, smelting and so on (see Figure 1) [1]. Under the action of microorganisms [4], the various forms of mercury present in water are converted to methylmercury [5], which enters fishes through the enrichment effect of the food chain [6,7]. This phenomenon is called bioaccumulation [8].
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