Pigment dispersion by prolactin in cultured xanthophores and erythrophores of some fish species

The direct effects of a pair of tilapia prolactins (tPRL(177) and tPRL(188)) and of ovine prolactin (oPRL) on cultured xanthophores and erythrophores isolated from some fish species were examined. Cultured xanthophores of the Nile tilapia, paradise goby, and medaka responded to tPRL(177) and oPRL at concentrations of less than 100 nM by pigment dispersion, whereas tPRL(188) had an effect only at concentrations of 10 mu M or more. Swordtail erythrophores also responded to prolactin even in winter. It is likely, therefore, that in fish species possessing many xanthophores or erythrophores in their skin throughout the year, these cells respond to prolactin all the time. In fall and/or winter, prolactin had little or no effect on xanthophores isolated from the dark chub and rose bitterling or on erythrophores from the tilapia and paradise goby. However, it was shown that xanthophores of the rose bitterling and erythrophores of the tilapia responded better to prolactin in spring and/or summer as compared with fall and/or winter. Such seasonal change in the responsiveness of the cells to prolactin implies the involvement of the hormone in nuptial coloration and an augmentation of red and/or yellow skin color by pigment dispersion in the spawning season. Prolactin-induced pigment dispersion within erythrophores isolated from the red region of tail fins of the rose bitterling assuming nuptial coloration also lends support to this supposition. (C) 1996 Wiley-Liss, Inc.