 fish sexual development is sensitive to exogenous hormone manipulation , and salmonids have been used extensively as environmental sentinels and models for biomedical research . 
 we simulated maternal transfer of contaminants by microinjecting rainbow trout ( oncorhynchus mykiss ) and chinook salmon ( oncorhynchus tshawytscha ) embryos . 
 fish were reared for 6 months and sexed , and gonads were removed for histology and measurement of in vitro steroid production . 
 analysis of fat samples showed that dichlorodiphenylethylene ( dde ) levels , o , p'm - dde and p , o , p'-dde isomers , were elevated 6 months after treatment . 
 a preliminary study showed an increased ratio of males to females after treatment with 80 mg / kg and 160 mg / kg of the xenoestrogen o , o , p'-dde . 
 one fish treated with 160 mg / kg o , o , p'-dde had gonads with cells typical of both males and females . 
 a follow - up study , using more fish and excluding the highly toxic 160 mg / kg o , o , p'-dde dose , showed no effect on sex ratio or gonadal histology . 
 embryonic exposure of monosex male trout , monosex female trout , and mixed sex salmon to o , o , p'-dde , p , o , p'-dde , mixtures of dde isomers , and octylphenol failed to alter sexual development . 
 we observed no treatment - dependent changes in in vitro gonadal steroid production in any experiments . 
 trout exposed in ovo and reared to maturity spawned successfully . 
 these results suggest that mortality attributable to the xenoestrogens o , o , p'-dde , chlordecone , and octylphenol , and the antiandrogen p , o , p'-dde , is likely to occur before the appearance of subtle changes in sexual development . because trout appeared to be sensitive to endocrine disruption 
 , we can not dismiss the threat of heavily contaminated sites or complex mixtures to normal sexual development of salmonids or other aquatic organisms.imagesfigure 1figure 2figure 3 
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