Aggression inTilapia affects immunocompetent leucocytes

Social interactions are typical behavioral patterns serving to regulate life in a group. These interactions may develop into aggression, which causes stress in the defeated animal. We used Tilapia, a commercially important fish which is aggressive, to examine how this behavior affects them and whether it induces alterations in leucocytes. Compared to dominant fish, subordinate ones had elevated glucose levels and hemolytic blood sera. In addition, cells from blood and pronephros of subordinates, when compared to dominant fish, showed qualitative changes characterized by granulocytosis and lymphopenia. Furthermore, leucocytes revealed cytoplasmic and karyoplasmic vacuolation, indicating cellular disintegration. These morphological alterations were also accompanied by impaired leukocyte function and thus may increase susceptibility to diseases and neoplasia.