Abstract
Male longear ( Lepomis megalotis) and pumpkinseed ( L. gibbosus) sunfish showed high levels of aggression when kept in 25 °C water under both long and short photoperiod. Lower water temperatures (11 ° to 13 °C) inhibited both aggression and nesting. Long photoperiod (16 hr light : 8 hr dark) induced nesting by both species in 25 °C water but only by longears in 11 ° to 13 °C water. Short photoperiod (8 hr light : 16 hr dark) inhibited nesting in both species. Injection of human chorionic gonadotrophin induced nest digging in both species under short photoperiod in 25 °C water but not in 11 ° to 13 °C water. HCG had no obvious effect on aggression. Both species dug nests more readily in visual isolation than when in visual contact with conspecifics. Androgen secretion, as assayed by nest digging, is controlled by photoperiod. The level of aggression depends on water temperature and does not seem to be influenced by gonadotrophins or androgens.
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