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 eryt hrophores isolated from some fish species were examined. Cultured xant hophores of the Nile tilapia, paradise goby, and medaka responded to t PRL(177) and oPRL at concentrations of less than 100 nM by pigment dis persion, 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 m any xanthophores or erythrophores in their skin throughout the year, t hese cells respond to prolactin all the time. In fall and/or winter, p rolactin had little or no effect on xanthophores isolated from the dar k chub and rose bitterling or on erythrophores from the tilapia and pa radise goby. However, it was shown that xanthophores of the rose bitte rling and erythrophores of the tilapia responded better to prolactin i n spring and/or summer as compared with fall and/or winter. Such seaso nal 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 isol ated from the red region of tail fins of the rose bitterling assuming nuptial coloration also lends support to this supposition. (C) 1996 Wi ley-Liss, Inc.