Granular epithelioid cells in the kidney of the Atlantic salmon (Salmo salar).

Two-year-old salmon at the migrating stage were kept in two different aquaria, the one containing seawater, the other freshwater. The fish kept in seawater showed retarded growth at the beginning of the year, but their growth had caught up with and passed the freshwater fish by the end of the year. At this time, 69 out of 79 of the freshwater fish died without any evident reason. When the fish were in seawater or freshwater at the biologically appropriate time, the number of granular epithelioid cells was equal in both groups. But the fish forced to remain in freshwater subsequently developed a considerably higher number of epithelioid cells. This may reflect an effort to maintain normal blood pressure.