Effect of salinity and ration size on macrophage phagocytosis in juvenile black sea bream (Mylio macrocephalus)

The effects of salinity adaptation and ration size on macrophage phagocytosis were assessed in black sea bream ( Mylio macrocephalus ) juveniles. Salinity had no effect on phagocytosis in fish that were fed a 10% ration size. Reducing ration size from 10 to 5% resulted in a significant reduction in splenic and pronephric macrophage phagocytosis of fish adapted to hyper-(33 p.p.t.) and hypo-osmotic (6 p.p.t.) salinities. The fish that were adapted to an iso-osmotic salinity (12 p.p.t.) and fed a 5% ration size were able to maintain macrophage phagocytic activity at levels comparable to those of fish that were fed a 10% ration size. It is proposed that the adaptation of sea bream to an iso-osmotic medium is beneficial in that it stimulates the immune response through activation of macrophage phagocytosis.