Sex steroids relative to alternative mating behaviors in the simultaneous hermaphrodite Serranus subligarius (Perciformes : Serranidae)

This study is the first investigation of reproductive endocrinology in a si multaneously hermaphroditic teleost, the belted sandfish (Serranus subligar ius). We address two questions: (1) Do steroid hormone levels vary during t he spawning season or during the daily spawning cycle of sandfish? (2) Do h ormone levels vary relative to an individual's phenotype-size, frequency of spawning and aggressive behaviors, and proportion of testis in the gonad? We analyzed circulating estradiol-17 beta (E2), testosterone (T), 11-ketote stosterone (20 beta S), 17 alpha,20 beta,21-trihydroxy-4-pregnen-3-one (20 beta S), and 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (DHP) concentration s in a field population. only E2 levels were significantly higher at the ne w and full moon, suggesting peak periods of vitellogenesis at these times. Naturally spawning sandfish were sampled every 2 h during the photophase of a 25-h period (12 pm to 1 pm the following day) and gonadosomatic index, d egree of oocyte hydration and ovulation, and plasma levels of E2, T, DHP, a nd 20 beta S were analyzed. E2 and T levels did not vary during photophase, suggesting continuous recruitment of oocytes into vitellogenesis. The 20 b eta S levels peaked around the time of final oocyte maturation. Since frequ ency of spawning behaviors changes with body size, we captured individuals of various sizes throughout the spawning season and analyzed circulating le vels of hormones. 11KT and 20 beta S levels increased significantly with bo dy size. In 1992, we quantified frequency of spawning and aggressive behavi ors, circulating T and 11KT levels and testicular mass relative to ovotesti s mass in focal animals. 11KT levels tended to be positively correlated wit h frequency of courting male behavior, but were unrelated to the frequency of aggressive behavior or testis mass. Because hormone levels increased wit h size and frequency of each spawning behavior changes with size, we propos e that sex steroids influence growth-related changes in spawning tactics of individuals, (C) 2000 Academic Press.