The objective of this study was to characterize the reproductive seasonality of slimy sculpin (Cottus cognatus), a small-bodied, benthic spring spawning species. Sculpin are unique compared with other temperate fish species because they have a reproductive pattern where gonadal maturation occurs over winter in northern areas of its distribution. Previous studies have involved pre-spawning sampling (early spring in North America) and post-spawning sampling (early fall in North America). However, seasonal changes in gonadosomatic index, hepatosomatic index, condition factor, and in vitro gonadal production of estradiol (E2) and testosterone (T) in females and T and 11-ketotestosterone (11-KT) in males have not been characterized. Following a summer quiescent period, female sculpin showed an increase in gonadal hormone production during the fall, which was associated with increases in gonad and liver sizes, however males experienced a much shorter resting phase following spawning in May. Elevated production of both T and 11-KT appears to both signal the initiation of gonadal growth in September and contribute to gonadal maturation over the winter. This study is important because it is the first characterization of the seasonal reproductive pattern in sculpin and it describes the patterns of gonad development and seasonal changes in condition and liver size in this species as it prepares for spawning.

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