A recent study found that the popular aquarium fish, cichlids, had levels of aggression that corresponded to the size and complexity of their habitats. Cichlids living in their native Nicaraguan lake had significantly lower aggression than those in a typical household aquarium. Some home setups cram fish in tightly, for example, 12-15 fish in a 55-gallon tank leaves only 3 gallons for each fish. Without space or adequate hiding spaces, less aggressive fish are at the mercy of their more hostile tank mates. In uncomfortable conditions like these, it is no wonder that pet stores label cichlids as highly aggressive.
If aquariums cause stress and behavior issues to the fish who live within their confines, the fish left in the wild are not faring well either. The aquarium trade has contributed to the decline in many species of fish and coral as dealers take indiscriminately from oceans and freshwater lakes and rivers, often destroying the ecosystem causing a further decline in species.
When you think about it…should we really be confining fish to a few gallons of water for our viewing enjoyment?