Fig. 6. Changes in the density of the four mitochondrion-rich cell types following transfer from freshwater to seawater (A) and vice versa (B). The data are expressed as the mean ±S.E.M. of four individuals. Columns with different letters are significantly different (P<0.0125, the Bonferroni/Dunn test). red, type-I cell; cyan, type-II cell; magenta, type-III cell; green, type-IV cell.