The effect of prolactin on fanning behavior in the male three-spined stickleback, Gasterosteus aculeatus L.

The effect of administration of homologous prolactin on fanning behavior, an important aspect of parental care in sticklebacks and many other teleost fish, was studied. Prolactin was administered by implantation of an additional pituitary prolactin lobe in the dorsal body musculature of males with a nest without eggs. The low but rather constant level of fanning behavior is significantly increased from Day 6 to Day 12 after administration of the prolactin lobe. The implantation has no noticeable effects on cell and nuclear size or on the ultrastructure of the in situ prolactin cells of the recipient fish. Recovered prolactin lobe implants show two categories of prolactin cells. The major category consists of cells that are well developed and, similar to in situ prolactin cells, show structural signs of high secretory activity. The other prolactin cell category in the implants shows signs of cellular involution. Ten days after implantation, the first category predominates, and 16 days after implantation the second category. Prolactin lobe implantation increases the number of mucocytes in the epithelium of the skin, in particular at Day 10, and to a lesser extent at Day 16. This is considered evidence for a transient rise in blood prolactin levels in the recipient fish. We conclude that prolactin stimulates fanning behavior in male sticklebacks.