Prolactin Diminishes Courtship Behaviour and Stimulates Fanning in Nesting Male Three-Spined Sticklebacks, Gasterosteus Aculeatus

The male stickleback displays a gradual change in reproductive behaviour as the eggs develop over the nesting cycle, with a decrease and cessation of courtship behaviour (e.g. zigzag dance) and an increase in fanning, i.e. ventilation of the nest and eggs. Prolactin (PRL) is known to stimulate fanning behaviour in several teleosts, including the stickleback, in which furthermore the PRL cells of the pituitary have been found to be more active during the later parental phase than during the initial sexual phase of the nesting cycle. In order to determine whether courtship behaviour is also affected by PRL, we measured zigzags (frequency of the behaviour towards a female/30 min), in addition to measuring fanning (seconds/30 min), both before and after PRL administration in nesting males without eggs. Treatments were performed by intraperitoneally injecting nesting males with either saline, ovine PRL (7.8 μg/fish) or coho salmon, Oncorhynchus kisutch, PRL (0.001, 0.01, 0.1 and 1.0 μg/fish). Saline injections affected neither fanning nor zigzag behaviour. Ovine PRL increased fanning, but had no effects on zigzags. Time spent fanning increased and zigzag frequencies decreased following injections of salmon PRL at all doses. Our results suggest that the increase in prolactin activity previously observed during the stickleback parental phase is involved in the control of both the increase in fanning and the decrease in courtship behaviour as the eggs develop over the nesting cycle of this species.