Steroid profiles during spawning in male common carp

The profiles of testosterone (T) 11-ketotestosterone (11-KT), 17 alpha-hydroxy-4-pregnen-3-one (17-P), and 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17,20 beta-P) were determined in groups of spermiating male common carp (Cyprinus carpio) which were or were not mated with females and subjected to an increase in water temperature, a treatment which usually induces females to spawn. The steroid levels were correlated with changes in gonadotropin (GtH). All males mated with ovulatory females showed a GtH surge and spawned. Two distinct classes of these spawned males were differentiated based on their initial androgen levels and hormone profiles. Androgen levels were initially elevated in the "high" males. In these fish there was a very rapid shift in the steroidogenic pathway from androgen to progestogen production coincident with the GtH surge. In the "low" males, 17-P levels rose significantly in response to the GtH surge, but there was no steroidogenic shift. In the males mated with nonovulatory females, the levels of 17-P, 17,20 beta-P, T, and 11-KT all increased coincident with a small rise in GtH; there was no steroidogenic shift. In the unmated males, the steroid profiles were similar to those in the nonspawned fish, except that T and 11-KT levels were significantly lower in comparison. In all groups, 17-P rose higher than 17,20 beta-P, and 11-KT was generally the predominant androgen. A model is proposed which explains the steroidogenic shift in the "high" males. This involves the inhibition of androgen biosynthesis by 17,20 beta-P or by a related progestogen.