Thermal tolerance traits of juveniles of the ayu Plecoglossus altivelis and Japanese flounder Paralichthys olivaceus evaluated by their caudal fin cells

The thermal tolerances of the ayu Plecoglossus altivelis and Japanese flounder Paralichthys olivaceus were evaluated by assaying the primary culture cells and the free cells from their caudal fins (at 43°C for 2 h) in comparison with the whole body tolerances of juveniles (at 30°C for the ayu and 32°C for the Japanese flounder). Primary culture cells and free cells were assayed separately and similar results were obtained for each type of cells. The thermal tolerance values observed in the whole body were significantly correlated with the values obtained from both the primary culture cells and the free cells. These results suggest that there is a significant correlation between the in vivo and in vitro thermal tolerances in these fish. In the case of the ayu, significant differences were observed between two lines for the mean tolerance values evaluated by all three methods. This finding suggests that cell assays with primary culture cells or free cells from a caudal fin clip could be useful for evaluating the genetic variation and genetic mechanisms of thermal tolerance of fish.