however, may not be developed until the successful reproduction and growth 

 rate of second-generation individuals has been shown to be unaffected. 



Biochemical and Physiological Endpoints 



A third group of endpoints has been explored by various investigators 

 and has shown promise. These endpoints are related to the changes in blood 

 characteristics and enzyme activity, changes in metabolic rates, or other 

 physiological changes. A deficiency of this type of endpoint in long-term 

 tests is that it usually requires sacrificing of the organisms or submit- 

 ting the organism to unnatural conditions which may change metabolic res- 

 ponses caused by restraint of movement, excitement, or lethargy. Further, 

 the ecological significance of these endpoints and the actual detrimental 

 effects on the organism are difficult to interpret. Change in these para- 

 meters does not, a priori, indicate a disadvantage to survival characteris- 

 tics or growth characteristics of the organisms. These endpoints have the 

 further disadvantage that they must be described and interpreted by 

 scientists. Tests of this kind cannot be delegated to field investigators 

 or relatively unskilled laboratory personnel who must be employed in large- 

 scale monitoring or surveillance programs. They have substantial value for 

 sophisticated research and identification and classification of potential 

 or real toxicants where results of these physiological criteria can be 

 equilibrated with results easily interpreted in terms of ecological conse- 

 quences that have practical value. 



Behavioral Endpoints 



A fourth type of endpoint may be described as a behavioral variation 

 which is considered to be inhibitory to growth and reproduction or long- 

 term survival. In various experiments it has been demonstrated that be- 

 havioral aberration will prevent spawning at toxicant levels where other 

 measurable parameters appear to be unaffected. Changes in degree of 

 mobility, increase or decrease of opercular ventilation, and avoidance 

 reactions have all been used to indicate adverse physical conditions for 

 the individual organism. As in the biochemical endpoints, interpretation 

 of the observed results in terms of ecological and field significance is 

 difficult unless comparative tests with other ecologically significant end- 

 points are made. 



FACTORS AFFECTING VALIDITY OF ENDPOINT 



After a significant endpoint for bioassay has been selected with care- 

 ful attention to the objective sought, a series of potential limitations of 

 the test procedure itself will determine the validity of the toxicant 

 values produced when the endpoint is reached. 



The first consideration is the health of the test species. The test 

 fish must be in good physical health, either having been laboratory-reared 

 under controlled and disease-free conditions or captured from a known wild 

 stock where fish have not been stressed by pollutants or other physical 

 factors. Disease, starvation, or careless handling before tests will 



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