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Vitellogenin Production by Fishmeal-Containing Diets in Male Tilapia (Oreochromis Mossambicus)
Citation:
DAVIS, L. K., T. E. Hirano, AND E. G. Grau. Vitellogenin Production by Fishmeal-Containing Diets in Male Tilapia (Oreochromis Mossambicus). Presented at Triangle Consortium on Reproductive Biology meeting, Research Triangle Park, NC, February 06, 2010.
Impact/Purpose:
In order to examine whether components ofcommercial fish feed might induce Vg production, Vg levels were measured every 10 days in male tilapia fed either commercial feed, commercial feed treated with Ez (20 mg/kg of feed), or a diet consisting of 50% squid and 50% mixedvegetables.
Description:
In a number of fish species, male plasma has been shown to contain substantial levels of l7~estradiol (E z) and in certain cases, vitellogenin (Vg), an Ez-induced precursor of egg yolk protein that is specific to females. The presence ofEz and Vg in males raises questions about their etiology and may confound the assessment of environmental endocrine disruptors in aquatic species. In order to examine whether components ofcommercial fish feed might induce Vg production, Vg levels were measured every 10 days in male tilapia fed either commercial feed, commercial feed treated with Ez (20 mg/kg of feed), or a diet consisting of 50% squid and 50% mixedvegetables. Over 40 days,plasmaVg offish fedcommercialfeed remainedconstantat37mg/ ml, while levels offishfedEzsignificantlyincreasedto45mg/ml.PlasmaVg of squid/vegetable-fed fish declined over time to often undetectable levels. Expression of three Vg genes (Vgs A-C) in the liver of squid/vegetable-fed fish decreased to 0.6-3.2% oflevels in control fish after 40 days while expression ofVgs A-C in Ez-fed fish increased by up to 25 fold. Custom made fishmeal-and soy-based diets were also tested for Vg induction potential. While plasma Vg was reduced after 20 days in male fish fed the soy-based diet, plasma levels were still detectable. The data suggest that Ez, most likely from the fish meal component of the feed, induced gene expression and production ofVg in male tilapia. Sustained use ofthis diet will maintain Vg production, and may mask effects in studies of estrogenic endocrine disrupting compounds. In apreviousstudy, we found that asingle injection ofo,p'-DDE (l00 ug/g) increased gene expression ofVgs A-C, but did not alter plasma Vg levels, possibly due to high circulating Vg. Feeding experimental fish a diet free of sex steroids and phytoestrogens may provide a more sensitive and suitable model to assess the effects of endocrine disruptors in fish. This is an abstract ofa proposed presentation and does not necessarily reflect EPA policy .