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Aquarium Fish Aggression

October 21, 2011

Bigger tanks and richer environments reduce aggression in popular pet fish.



Preventing fish fights…I’m Bob Hirshon and this is Science Update.

You’d be pretty cranky if you shared an unfurnished studio apartment with several strangers.  But many pet fish suffer similar conditions, according to behavioral ecologist Ronald Oldfield of Case Western Reserve University.  He studied tropical fish known to bite and even kill each other in tanks, and found that the violence subsided in larger tanks with more complex features, like rocks and plants. 

RONALD OLDFIELD (Case Western Reserve University):

You reach a threshold at which the tank is big enough, and the habitat is complex enough, they stop being intensely aggressive.  And it seems like they kind of switch aggression on when you reduce these factors to a certain degree.


But small differences in the number of fish in the tank had much less impact.  Oldfield says that according to behavioral theory, having fewer competitors actually makes fish more territorial, which may offset any advantages to thinning the crowd. I’m Bob Hirshon for AAAS, the Science Society.