While testosterone is the primary androgenic male steroid found in mammals, 11-keto testosterone (11-KT) is a second key andogenic steroid found in fish. It occurs in males together with testosterone in amounts which vary from less than 1 ng/ml to as much as 50-100 ng/ml, depending on the species and the stage of the reproductive cycle. In the sea bass, testosterone concentrations are generally higher than 11-KT, with peak levels found after the spawning season. 11-KT, on the other hand, remains at levels less than 1 ng/ml but rises abruptly to 4-6 ng/ml during spermiation at the height of the spawning season (1). 11-KT also shows individual variations in Arctic char, with dominant males having significantly higher 11-KT levels (2).
1 Prat, F., Zanuy, S., Carrillo, M., et al. Seasonal changes in plasma levels of gonadal steroids of sea bass, Dicentrarchus labrax L. Gen Comp Endocrinol 78, 361-373 (1990)
2 Elofsson, U.O.E., Mayer, I., Damsgård, B., et al. Intermale competition in sexually mature arctic char: effects on brain monoamines, endocrine stress responses, sex hormone levels, and behavior. Gen Comp Endocrinol 118 450-460 (2000)
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