An assessment of the reproductive cycle in black rockfish, Sebastes melanops (Girard, 1856) on the central Oregon Coast : a blood plasma protein and sex steroid used as potential indicators of sex and stage of gonadal maturity

Graduation date: 2007Because of large declines in abundance of many Eastern Pacific rockfish populations (Genus Sebastes), there has been an increasing effort to improve our understanding of the role of spawning population characteristics and individual reproductive success in recruitment variability and population dynamics. Current methods for assessing sex and maturational status in rockfishes are lethal, so fishery managers would benefit from a non-lethal method to assess the reproductive potential of rockfish populations. I developed a biochemical assay to determine sex and stage of female maturity in black rockfish (Sebastes melanops) using a blood plasma indicator vitellogenin (VTG). The specific objectives of this research were to: 1) describe the annual hormonal and gonadal changes associated with reproduction and 2) describe the timing of reproduction in female black rockfish of different age classes. \ud Estradiol-17β (E2) and VTG concentrations were compared with histologically determined ovarian stages of female maturity (i.e. pre-vitellogenic, early vitellogenic, mid-vitellogenic, post-vitellogenic, oocyte maturation, and post-spawned) from 325 female black rockfish sampled by hook-and-line from the central Oregon coast from September 2003 to January 2005. I also measured E2 and VTG in male fish from the same time period. VTG concentrations detected in field-collected blood samples reflected the seasonal cycle reported in previous studies. Mean concentrations of VTG in mid-vitellogenic, post-vitellogenic, and females undergoing oocyte maturation can be used to distinguish between pre-vitellogenic females and early vitellogenic females during the spawning season (P<0.05). Females can be distinguished from males based on VTG concentrations (P<0.0001), with the exception of pre-vitellogenic and post-spawned females (immature fish and mature female fish in non-reproductive summer months). Mean E2 concentrations were not as accurate for identification of sex and each individual stage of female maturity, although mid-vitellogenic and post-vitellogenic females had significantly higher concentrations of E2 than pre-vitellogenic females (P<0.05). Mean concentrations of E2 in mid-vitellogenic females, post-vitellogenic females, and females undergoing oocyte maturation were higher than in males (P