A unique study involving the Midas cichlid (Amphilophus citrinellus) in a variety of environments has served to highlight the importance of the size and layout of a home aquarium on the behavior of this territorial species. This is believed to be the first scientific study of its type, looking at the effect of typical aquarium set-ups on aggression in ornamental fish.
Measuring aggression
Ronald Oldfield, an instructor of biology at Case Western Reserve University in Cleveland, Ohio, observed this species within its native range in a crater lake in Nicaragua, in a large artificial stream in a zoo, and in tanks of the sizes typically used by pet owners.
The study focused on juvenile fish, so as to exclude aggressive behavior related to mating. Also, resources such as food and shelter were removed prior to observation, in order to eliminate direct competition.
Along with the size of the environment, Oldfield also tested the complexity of an environment and the impact of a varying number of fish housed within the 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 reduced harmful aggressive behaviors, helping to ensure the health and well-being of the cichlids housed in these surroundings.
Oldfield quantified aggressive behavior as a series of displays and attacks separated by at least a second. Displays are body signals such as flaring fins. An attack could be a nip, chase, or charge at another fish. In aquariums, these behaviors can lead to injury and in extreme cases to death.
Aggressive behavior was not correlated with small-scale changes in either group size or habitat size alone. However, a significant difference was observed in environments sufficiently large and complex: fish spent less time exhibiting aggressive behavior here.
"This more natural environment elicits increased signs of natural behaviors, which are more interesting to observers," added Oldfield. "And, for the fish themselves, their lives can be vastly improved with these simple changes to their environments."
Looking to the future
Oldfield emphasizes that he is not aiming to support any extreme agendas. "I'm not trying to ban human use of animals as pets or in aquaculture generally. I just think that if we are going to interact with them, then we should be as informed as possible about their behaviors."
Looking to the future, Oldfield said "This study might even help us to better understand how human behavior changes when people are placed in different social environments. Violence in prisons might be linked in part to the smaller space and reduced stimuli."
It is important to note, however, that this study involved just a single species of cichlid, which is recognized in the hobby as having a particularly aggressive temperament, and much more work is required in order to see how widely - if at all - these findings can be transposed to other groups of fish.