Methyl parathion reduces aggressive behaviour of male betta splendens

A previous work has indicated that fighting fish behaviour of Betta splendens can be used as a bio-indicator of heavy metal pollution. In this article, the effect of methyl parathion on the fighting behaviour of male Siamese fighting fish was investigated. The frequency and duration of opercular erection were taken as indicators of male aggressiveness towards another male. All male fish were housed in glass jars for 1-2 weeks prior to experiments. Sixteen naive males were randomly assigned to two experimental groups: methyl parathion (5 mg/L) and control. Males were placed in their respective treatment jars for 24 h, and then, each male was paired with another male of matching size in an 30x25x25 cm aquarium. The aquarium had an opaque divider to keep the two males separate for 10 min of acclimation period. The divider was then removed and behavioural measurements were taken for another 10 min. The results showed that fish placed in methyl parathion had significantly lower aggressive behavlour, as indicated by lower frequency and shorter duration of opercular erection. It can be concluded that aggressive behaviour of male Betta splendens is a suitable bio-indicator of organophosphate pollution.