Stress caused by social interaction and its effect on susceptibility to Aeromonas hydrophila infection in rainbow trout Salmo gairdneri

Juvenile rainbow trout were exposed slmultanously to social stress and to infection by the opportunistic ubiquitous bacterium Aeromonas hydropma. Social interaction between randomly chosen pairs was permitted for 11 h consecutively. After the fust hour the bacteria were either added to the water or were injected intramuscularly. As an indication of the stress syndrome, subordinate fishes showed enhanced ventdation frequency, elevated plasma glucose level, and increased leucocyte volume. In subordinates the pathogens spread to more organs and were found in greater numbers than m the dom~nant fishes, independent of the mode of bacterial applicahon.