Effect of Alcohol and Congeners on Aggressive Response in <i>Betta splendens</i>

Abstract

The aggressive response of 12 male Siamese fighting fish (Betta splendens) was measured before and after 6 hours of immersion in individual tanks containing one of 3 test solutions: 285 mg of ethanol per 100 ml, commercial bourbon whisky diluted to the same ethanol concentration, and a congener solution diluted to contain amounts of congeners similar to that of the second test solution and containing 10 mg of ethanol per 100 ml. Groups were reversed a week later so that 12 fish were tested as both control and test in all 3 conditions. The accumulated time the gill membrane of the fish was lowered in response to a 3-minute exposure to its mirror image was used as an index of aggressive response. In the ethanol solution the mean accumulated gill show increased by 11.42 seconds (p<.005), in the bourbon and congener solutions the aggressive response decreased by 24.75 (p<.001) and 19.33 sec (p<.005), respectively. In the congener solution 5 of the 12 fish showed no aggressive response whereas all the fish in the bourbon solution showed some residual aggression after the 6-hr immersion. The results suggest that the behavioral effects of congeners and ethanol involve different physiological mechanisms.