Rapid decline in the behavioral response of paradise fish (Macropodus opercularis) to prostaglandin F2 alpha treatment.

Prostaglandins (PGs) can affect sexual behavior in a range of vertebrates including goldfish, paradise fish, lizards, frogs, hamsters, and rats. Behavioral responsiveness to PG treatment has not previously been reported to correlate with reproductive condition. Earlier work (Villars et al., 1985) has suggested that in paradise fish, response to PG treatment may be limited to the period immediately following spawning. In the present experiment, prespawned females were tested for their response to intraperitoneal injection of PGF2 alpha (300 ng/g body wt) at 1 (n = 10), 3 (n = 8), or 5 (n = 8) days postspawning. Only pairs tested 1 day postspawning responded to PG-treatment of the female with spawning acts (curving or inverting). Moreover, 1 day PG-treated females showed significantly increased sexual motivation, as measured by the time the female spent under the nest with a nest-building male and by the frequency of female sexual solicitation, while the 3-day and the 5-day postspawning females showed no discernible response to PG treatment. Though differential behavioral experience had been suspected to account for female unresponsiveness seen in earlier work, it now seems possible that physiological changes post spawning may render the females unresponsive to PG treatment.