Reduced aggression in male Betta splendens after treatment with mercuric chloride

It has been suggested that variation in aggressive behaviour of male Betta splendens might be used as a bio-indicator for the presence of the heavy metal pollutants mercury and sodium azide. In this study, the effect of HgC ^l2 on aggressive behaviours of male Betta splendens was assessed. Aggressive behaviour was quantified as frequency and duration of opercular extension in response to an intruder (another male). In the experimental set up, a male Betta was placed in an aquarium. A glass jar fitted with an opaque cover and containing a second Betta male was situated in one corner of the aquarium. Records of opercular extension frequency and duration exhibited by the resident male were recorded over a 10-min test period during which the cover was removed from the jar permitting visual contact with the intruder. A second trial was conducted the next day between 10:00-12:00 pm. The aquaria and jars were filled with clean water under control and with polluted water under experimental conditions. The results showed that male Betta splendens placed in polluted water for 24 h had significantly lower opercular extension rates (13 ± 10.2) in response to an intruder compared to control fish placed in clean water (30.3 ± 9.1).