Seasonal variations in sex steroids and male sexual characteristics in Scyliorhinus canicula

Concentrations of testosterone, progesterone, Delta 4-androstenedione,dihyd rotestosterone,11-ketotestosterone, estrone, estradiol-17 beta, 5 alpha-and rostane, 3 alpha, 17 beta-diol, and 17 alpha-hydroxy,20 beta-dihydroprogest erone were determined by radioimmunoassays in the blood plasma and testicul ar homogenates of Scyliorhinus canicula. Samples were collected almost ever y month for 27 months. The weights and sizes of reproductive organs and spe rm reserves were also measured over the same period. Quantitatively, testos terone was the principal steroid present. Testicular and epididymal weights , sperm reserves, and clasper size varied-throughout the year, but not alwa ys in a synchronous fashion. Most of the testicular steroids had an annual peak, generally in February, except for progesterone. The plasma concentrat ions of progesterone, Delta 4-androstenedione, and androgens presented vari ous degrees of fluctuation over the year, but were not synchronized: maxima occurred during autumn-winter for androgens and progesterone, during sprin g for Delta 4-androstenedione. Thus, various aspects of S. canicula reprodu ctive function appear to be influenced by season, the sea temperature being , most probably, a major determinant in this respect. (C) 1999 Academic Pre ss.