Differentiation by morphine of two types of aggressive behaviour in the convict cichlid (Cichlasoma nigrofasciatum).

Morphie sulfate (5 mg/l and 10 mg/l) significantly decreased the amount of territorial aggression in the convict cichlid (Cichlasoma nigrofasciatum). The same doses had no effect on predatory aggression (ingestion of brine shrimp). The data suggest that previously demonstrated morphine receptor in the fish has functional properties.