Fish may take out their aggression on smaller fishes through a process called displaced aggression, a new study has shown.
Displaced aggression has been studied in primates before and scientists have shown that intermediate-ranking individuals may vent their anger on smaller individuals if they lose a fight with a more dominant individual. Now, researcher Oyvind Overli from the University of Norway has presented evidence to suggest a similar thing in rainbow trout, Oncorhynchus mykiss.
Overli suggested that this displaced aggression might help reduce stress caused by losing the initial fight with a more dominant specimen, since trout who were monitored during such disputes showed lowered levels of the stress hormone cortisol.