Morpho-physiological predictors of ovulatory success in captive striped bass (Morone saxatilis)

This study evaluates morpho-physiological characters as predictors of ovula tory success in cultured striped bass, Morone saxatilis, that could be used by farmers to select females for induced spawning. Diameter, size homogene ity and growth of ovarian follicles; blood plasma levels of testosterone (T ), oestradiol-17 beta (E-2) and vitellogenin (VTG); and in vitro maturation of oocytes, in response to a combination of insulin-like growth factor-I ( IGF-I, 100 nM) and 17,20 beta,21-trihydroxy-4-pregnen-3-one (20 beta-S, 290 nM) were examined for females prior to spawning induction and compared wit h their subsequent ovulatory response. Fish spawning within 8 days of impla ntation with pelleted analogue of mammalian gonadotropin-releasing hormone analogue (GnRHa; [D-Ala(6)-des-Gly(10)-NEt]-LHRH) were considered to have g iven a satisfactory maturational response. The in vitro assay was the most reliable predictor for ovulatory success. All fish whose oocytes completed final oocyte maturation (FOM) in vitro in response to the combination of IG F-I and 20 beta-S spawned, whereas, 12 out of 13 fish, whose oocytes did no t complete FOM in vitro, failed to spawn within 8 days of GnRHa treatment. The in vitro assay was field-tested on commercial farms, and correctly iden tified all four females that spawned out of the eight females that were giv en hormone treatment. Among the other measurements, follicle diameter best differentiated between fish that later spawned and those that did not spawn . Plasma T concentrations were greater on average in fish that spawned, but the technical complexity of the assay and overlap in T concentrations betw een fish that spawned and those that did not limits the value of this measu rement to farmers. There was no significant difference in follicle size hom ogeneity, follicle growth over the 2-week period prior to hormone treatment , or plasma levels of E-2 and VTG between fish that spawned and those that did not. (C) 2000 Elsevier Science B.V. All rights reserved.