The results of previous studies of aggression in territorial species may be potentially undermined by new research showing that fish do not react to reflections in the same way as they would react to a rival.
Mirrors have frequently been used to trigger responses in less self-aware animals such as birds and fish, but a recent study published in the journal Animal Behaviour demonstrated that Convict cichlids (Amatitlania nigrofasciata) reacted slightly differently when facing a true rival, as opposed to their reflection in a mirror.
The study author, Robert Elwood from Queen’s University in Belfast, likened the behaviour to a boxer: “If a fish is truly looking for a fight with its reflection, it will move quickly and ‘stay on its toes.’ However, if it's just posturing in front of a mirror, a 'boxer' can stand around and pose for ages.”
Russell Fernald at Stanford University in California commented “Scientists generally underestimate the cognitive abilities of fish. We have shown that cichlid fish can do logical reasoning. Fish can infer social rank by observation alone. So why should they be fooled by a mirror?"