Seasonal changes in the histology of the gonads and dorsal skin of the fathead minnow, Pimephales promelas

Abstract

In central Saskatchewan gonad weights of male and female fathead minnows reach peak values between June 1 and July 31. The precise timing of the peak seems to be determined by local weather (temperature). Gonad histology shows a predominance of early gametogenic stages during winter with gametogene sis being completed in the spring. The histology of the dorsal skin is similar in both sexes during the nonbreeding season but males develop a dorsal pad during the breeding season. Pad development involves seasonal changes in epidermal thickness, mucous cell number, and dermal connective tissue thickness. Males also lose their alarm substance cells briefly during the peak breeding period.