Environmental control of teleost reproductive cycles: a brief review

Abstract

Reports concerned with the environmental regulation of teleost reproductive cycles are critically reviewed. Photoperiod and temperature have been the most frequently studied environmental factors with respect to control of sexual cycling. Photoperiod may exert the dominant regulatory role in the salmonid family, but few species have been examined so no conclusive statement is presently possible. Both photoperiod and temperature may be important controlling factors in the cyprinid family, but inadequate controls prohibit meaningful interpretation. Temperature may be extremely important in regulating reproductive cycles in the cyprinodontiform fishes. Although the data are inconclusive, it appears that changes in daylength play some role in reproductive cycling in the gasterosteids. Photoperiod and temperature seem to interact in regulating the sexual cycles in the 2 periform species investigated.It is concluded that short term laboratory studies may lead to erroneous statements concerning the importance of exogenous factors in controlling annual reproductive cycles. Although photoperiod has been credited as the dominant environmental regulatory factor in many previous investigations, photoperiodism seems to be temperature sensitive in a majority of the teleost species studied. Responsiveness to exogenous factors appears to depend on the gonadal condition of the beginning controls (effects vary with season). Considerable variation is seen in the reproductive timing mechanisms among the teleosts and few generalizations can be made with regard to phylogenetic, geographic or ecological relationships of the fishes studied.