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Research Article |
School of Aquatic and Fishery Sciences,5
University of Washington, Seattle, Washington 98195 Northwest Fisheries Science Center,6
National Oceanic and Atmospheric Administration-National Marine Fisheries Service, Seattle, Washington 98112 Center of Reproductive Biology,7
Washington State University, Pullman, Washington 98164
ABSTRACT
Body growth during critical periods is known to be an important factor in determining the age of maturity and fecundity in fish. However, the endocrine mechanisms controlling oogenesis in fish and the effects of growth on this process are poorly understood. In this study interactions between the growth and reproductive systems were examined by monitoring changes in various components of the FSH-ovary axis, plasma insulin-like growth factor 1 (Igf1), and ovarian gene expression in relation to body and previtellogenic oocyte growth in coho salmon. Samples were collected from females during two hypothesized critical periods when growth influences maturation in this species. Body growth during the fall-spring months was strongly related to the degree of oocyte development, with larger fish possessing more advanced oocytes than smaller, slower growing fish. The accumulation of cortical alveoli in the oocytes was associated with increases in plasma and pituitary FSH, plasma estradiol-17beta, and ovarian steroidogenic acute regulatory protein (star) gene expression, whereas ovarian transcripts for growth hormone receptor and somatolactin receptor decreased. As oocytes accumulated lipid droplets, a general increase occurred in plasma Igf1 and components of the FSH-ovary axis, including plasma FSH, estradiol-17beta, and ovarian mRNAs for gonadotropin receptors, star, igf1, and igf2. A consistent positive relationship between plasma Igf1, estradiol-17beta, and pituitary FSH during growth in the spring suggests that these factors are important links in the mechanism by which body growth influences the rate of oocyte development.
estradiol, follicle-stimulating hormone, follicle-stimulating hormone receptor, growth hormone, oocyte development
1 Supported by a contract from the Bonneville Power Administration (93–056 to P.S.) and the National Marine Fisheries Service. Presented in part at the 7th International Symposium on the Reproductive Physiology of Fish, Japan (18–23 May 2003).
2 Correspondence: Penny Swanson, Northwest Fisheries Science Center, NOAA-National Marine Fisheries Service, 2725 Montlake Blvd. East, Seattle, WA 98112. FAX: 206 860 3467; penny.swanson{at}noaa.gov
3 Current address: Hawaii Institute for Marine Biology, P.O. Box 1346 (46–007 Lilipuna Rd.), Kaneohe, HI 96744.
4 Current address: Faculty of Agriculture, Kochi University, B200 Monobe, Nankoku, Kochi 783-8502, Japan.
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