Oldfield compared the behavior of Midas cichlids (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 focused on juvenile fish to remove aggressive behavior related to mating. Also, resources such as food and shelter were removed prior to observation to eliminate direct competition.

Along with environment size, Oldfield tested the complexity of an environment and the effects of number of fish within tanks.

The addition of obstacles and hiding places using rocks, plants, or other similar objects can increase the complexity of the aquarium environment.

He found that an increase in tank size and complexity can reduce harmful aggressive behaviors, and make for healthier fish at home.