Abstract:Clones are defined as groups of genetically identical fish. It is unclear whether clonal fish have identical reactions to toxicants. To address this question we used the static test method to investigate the acute toxicity of Hg2+ to clonal and common Japanese flounder, Paralichthys olivaceus. The clonal and common Japanese flounder in the experiments were produced by Beidaihe Central Experiment Station, with the average body length of (12.38±1.13) cm and the average body weight of (17.97±5.79) g. Fully aerated and filtered seawater [temperature (21±1.2)℃, pH 8.1-8.3, salinity 31.0, and hardness 6200 mg/L] was used in the tests. The results showed that the clonal Japanese flounder treated with high concentration of Hg2 first became anxious, rose to the water surface, and swam around in the aquarium, before they eventually stayed still at the bottom of the aquarium. The majority of common Japanese flounder treated with high concentration of Hg2 remained at the bottom all the time, except for only a few that occasionally swam to the surface. As the poisoning aggravated over the time, the common Japanese flounder began to rotate, swam rapidly or jumped up and down when touched by a glass rod; in the contrast, clonal Japanese flounder swam slowly around the aquarium regardless of the touch. Both the clonal and common Japanese flounder eventually stopped breathing and died with rigid bodies. At 24, 48 and 96 h, the median lethal concentrations of Hg2 to clonal Japanese flounder were 1.50, 0.86, and 0.84 mg/L respectively. The values of common Japanese flounder were 1.93, 1.04, and 0.90 mg/L respectively. These results suggested that the clonal Japanese flounder was more sensitive to Hg2 than the common Japanese flounder. A trend was observed in all groups of clonal Japanese flounder that they mainly died during the 8 hours starting from the occurrence of the first death; however, the death of the common Japanese flounder occurred evenly during the whole experiment.
