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EUGENE P. HAYDU 

 rationale concerned with determining toxicity by the bio- 

 assay technique. Among those most pertinent to this dis- 

 cussion mention should be made of the following: 



1. "Fish too often are considered as a 

 single species (like rats or people) instead of a multitude 



of species, many again distinctly and greatly different 

 from other related species. Because of the important 

 species, essential food organisms and water quality will 

 be different in different habitats, a single value or 

 concentration has very little applicability unless 

 appropriate margins of safety are incorporated." 



2. "Test organisms should be selected on 

 the basis of their economic importance in the area receiving 

 the discharge and their sensitivity or on the basis of 

 their importance in the food web of economically important 

 animals. In the event that organisms meeting these 

 criteria are not suitable or available for the confined 

 conditions of the tests, then substitute animals endemic 

 to the area may be utilized. Appropriate tests must be 

 undertaken to demonstrate the relative sensitivity of 

 economically important species and substitute species to 

 the test material so that meaningful interpretations of 

 the data can be made." 



For the most part, these guideline commentaries 



