Fig. 1. Summary representation of the epithelial diVerentiation in the gill and gut of euryhaline teleosts during acclimation to diVerent salinities. In the gut
during SW acclimation, cortisol induces apoptosis and proliferating cells become localized in troughs of intestinal folds, resulting in the high permeability.
During FW acclimation, PRL stimulates cell proliferation synergistically with cortisol, and apoptosis becomes localized at their tips, resulting in low permeability.
In the gill, coordinated changes in proliferation, diVerentiation, transformation and apoptosis result in increased ion uptake chloride cells in
freshwater and increased salt secretory chloride cells in seawater. The GH/IGF-I and cortisol axes interact to increase salt secretory chloride cells, and prolactin
and cortisol interact to increase ion uptake chloride cells, but the cell turnover pathways through which these hormones control gill chloride cells
has not been examined.