Effects of Melatonin, Serotonin, and Naloxone on Aggression in Isolated Cichlid Fish (Aequidens pulcher)

Publisher Website
Google Scholar
Abstract
Intracranial injections of 10 μg melatonin, with or without 4 μg naloxone, result in reduced aggressive responsiveness by the cichlid fish Aequidens pulcher to a mirror presented 20 min later. Naloxone, when administered on its own, had no behavioral effect. Intracranial injections of 25 μg serotonin-creatinine sulphate complex (5HT-CS) also reduced aggression. 5HT-CS's action was abolished if the injection included 10 μg S-adenosyl homocysteine (SAH), which inhibits the conversion of serotonin to melatonin. This suggests that the behavioral action of 5HT-CS may be mediated by its conversion to melatonin. There is inconclusive evidence to suggest that 37.5 μg 5HT-CS, administered in conjunction with 10 μg SAH, may reduce aggressiveness; injection of 50 μg 5HT-CS, with or without 10 μg SAH, induced a pronounced escape behavior which precluded any measurement of aggressiveness in the fish.