Differences in aggression between wild-type and domesticated fighting fish are context dependent

We investigated differences in aggression between wild-type Betta splendens, Betta smaragalina, two domesticated strains of B. splendens selectively bred for cockfight-like contests and appearance, and Betta sp. mahachai, an unclassified Betta variety. We tested the fish for aggression once they reached sexual maturity as well as during adulthood. We used a combined mirror and video playback test and a mutual-viewing test to measure close-range gill extension and biting attempts as principal measures of aggression. As predicted, the short-finned domesticated strains were significantly more aggressive than wild-type B. splendens. However, the difference in aggression manifested itself only in the mutual-viewing test, which is the test that most closely resembled an actual fight. Betta splendens and the closely related B. smaragdina did not differ in aggression across the experimental contexts; however, B. sp. mahachai responded more aggressively to the combined mirror/video test than B. splendens. Four of the five groups of fighting fish tested responded significantly more aggressively to video images of an aggressive conspecific male than to blank screen controls, suggesting that video playback can be a useful tool for measuring aggression in fighting fish. Our results are relevant for improving our understanding of key aspects of territorial aggression in teleost fish as well as for developing the most reliable ways of measuring them. (c) 2006 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.