An interdisciplinary approach is a prerequisite in achieving an overall view on the problems ofxenobiotic- induced reproductive disturbances in fish. At present, the greatest challenge to this problem is the translation ofsubtle functional deficits within individuals into population-level effects and this will require better field observations and laboratory studies to simulate field exposures. Furthermore, a complete risk assessment of the effects ofxenobiotics or xenoestrogens on fish re- production will require good reproductive toxicity test- ing, defined as the occurrence ofadverse effects on the reproductive system that may result from exposure to agents from exogenous sources. The toxicity may be expressed as alterations to the reproductive organs or the related endocrine system or to progenies