Angry Fish Inhabit Most Home Aquariums

Fish can turn mean when their home is barren and boring, says new research.

(Image: KC Blanchett)

Home fish tanks and aquariums may at first appear to be tranquil environments, but look closely and you might see a glaring goldfish or a ticked off tetra.

A new study has found that ornamental fish across the U.S. - all 182.9 million of them - are at risk of becoming aggressive due to cramped, barren housing.

In other words, fish can turn mean when their home sucks, according to">a new study in the Journal of Applied Animal Welfare Science.

"The welfare of aquarium fishes may not seem important, but with that many of them in captivity, they become a big deal," project leader Ronald Oldfield, an instructor of biology at Case Western Reserve University, said in a press release.

Oldfield's paper is the first to scientifically study how the environment of home aquariums affects the aggressive behavior of ornamental fishes. The findings are in keeping with related research, though. For example, earlier this year I reported on how cramped tank conditions are turning sea urchins into cannibals.

For this latest study, Oldfield compared the behavior of Midas cichlid (Amphilophus citrinellus) in a variety of environments: within their native range in a crater lake in Nicaragua, in a large artificial stream in a zoo, and in small tanks of the sizes typically used to by pet owners.

The study looked at just juvenile fish in order to remove the possibility of aggressive behavior related to mating. The experiments were also set up so that the fish weren't competing for food and shelter.

In addition to tank size, he tested the complexity of an environment and the effects of the number of fish within tanks. "Complexity" in this case refers to the addition of obstacles and hiding places, such as rocks, plants, and other objects. Tanks with more complexity, and of a larger size, helped to reduce aggressive behaviors.

Tempers were observed to literally flare, however, in the less desirable aquariums, with perturbed fish flaring their fins. But that was on the low end of the anger spectrum. Very ticked off fish nipped, chased, charged, and even murdered each other. (Similar attacks and killings have been observed before among captive great white sharks.

Oldfield suspects cramped, barren environments for humans may also serve as breeding grounds for comparable negative behaviors.

"This study might help us to better understand how human behavior changes when people are placed in different social environments," he said, suggesting that prisons fall into that extreme "different" category.

From the fish's perspective, life in a too-small and dreary tank might even feel like a jail cell does to us.

So if you do have a fish tank at home, give it the once over to see if a replacement or remodeling job is needed. If you plan to set up a new aquarium, don't select the cheap, stagnant water models that will have you flushing your pet investment down the toilet soon.

You needn't devote as much time, space and water as the fish enthusiast in the below video did, but check out the 1200-gallon setup for inspiration.