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EFFECTS OF GENISTEIN ON THE REPRODUCTIVE DEVELOPMENT OF STRIPED BASS (Morone saxatilis).
Pollack, Sara1, Ottinger, Mary Ann1, Woods, , L. Curry 1, 1
ABSTRACT- Striped bass raised under culture conditions are fed a variety of commercial feeds at different stages of development. Commercial feeds often contain up to 40 % soybean meal which is used as an inexpensive alternative protein source. Soybeans contain isoflavones, the most abundant of which is genistein. Genistein is a potent phytoestrogen, capable of acting on estrogen receptors. During the early juvenile life stage, sexual differentiation is sensitive to exogenous substances in the environment which may override the reproductive hormone axis. Previous studies demonstrated that significant levels of vitellogenin (VTG) were produced by juvenile striped bass when they were injected with estradiol benzoate (EB). If genistein affects reproductive development in striped bass, this would significantly impact the growth as well as sexual differentiation in these fish being fed diets with higher levels of soybean meal. This study was designed to determine if purified genistein in a commercial feed affects the reproductive development of juvenile striped bass during a potentially sensitive stage of maturation. Histological analysis of the gonadal tissue was conducted to assess the impact of genistein on cell differentiation. Examination of vitellogenin production will determine levels of VTG in the blood plasma via induction of this potent phytoestrogen. Seventy-two striped bass fingerlings of mean weight 98 g (n=18/treatment) were randomly assigned to four diets containing varying levels of genistein (0, 2, 4, and 8 mg/g diet). At the end of the six week study period, animals were sacrificed to obtain plasma and gonadal tissue samples for analysis. Results showed the various treatment levels of genistein had no significant effect (p<.05)on the growth of the fish. Histological samples revealed little effect on gonadal differentiation. The relative importance of the precise timing and potency of exposure to affect reproductive function in striped bass may be critical to understanding, in this examination, the capacity for genstein to induce a physiological response.
KEY WORDS: genistein, juvenile striped bass, vitellogenin, reproductive development