COMPARATIVE-STUDY OF REPRODUCTIVE-BIOLOGY IN SINGLE AND MULTIPLE-SPAWNER CYPRINID FISH .2. SEX STEROID AND PLASMA-PROTEIN PHOSPHORUS CONCENTRATIONS

The dynamics and regulation of oogenesis in single and multiple-spawne r cyprinid fish showing group-synchronous oocyte development, was inve stigated in three species from the River Meuse (Belgium): the roach Ru tilus rutilus as a single spawner, and the bleak Alburnus alburnus and the white bream Blicca bjoerkna as multiple spawners. This paper comp ares the seasonal profiles of sex steroids (oestradiol-17 beta, testos terone and 17,20 beta-dihydroxy-4-pregnen-3-one) and plasma alkali-lab ile protein phosphorus. Different patterns of plasma oestradiol-17 bet a (E2) and plasma protein phosphorus (PPP) have been observed not only between the single and the multiple spawner fish, but also among the two multiple spawners. In roach, two increases of E2 levels were obser ved. The first occurred in September after a short gonadal quiescent p eriod, and coincided with the increase of the PPP at the onset of exog enous vitellogenesis. The second took place in spring before the spawn ing season. The low PPP recorded during that period probably reflected its rapid incorporation by the oocytes. In both multiple spawners, hi ghest values of PPP were recorded just before the spawning season. In white bream, the PPP declined progressively once the differentiation o f exogenous vitellogenic oocytes was completed before the onset of the spawning season. In bleak, PPP levels remained high throughout the sp awning season and corresponded to a sustained oocyte recruitment durin g the whole of this period. Regardless of the pattern of oocyte growth recruitment, the E2 concentrations were high in both multiple spawner species during the breeding season. In the three species, testosteron e levels remained low regardless of the maturation stage (ranging from 0.6 to 13.4 ng ml(-1)). Except for relatively high concentrations of 17,20 beta P in roach during final maturation and postspawning stages (20 and 28 ng ml(-1), respectively), low levels of this steroid were m easured in these cyprinids, and especially in the multiple spawner fis h. The role of this progestogen as the maturation inducing steroid is discussed. (C) 1997 The Fisheries Society of the British Isles