DISCUSSION 



The screening test data presented in this report should be viewed only as indicative of the 

 toxicity of the individual compounds. Our objective was limited to the identification of biologically 

 active agents that would be selectively lethal to larval lampreys. Laboratory procedures did not permit 

 the numerous test replications necessary for positive definition of the toxicity of each substance. For 

 this reason, conventional toxicity ratings have not been computed. 



Test results obtained with many compounds were undoubtedly influenced by the quality of 

 the water used. It should be borne in mind that widely divergent results with any particular compound 

 might be obtained were these tests to be repeated in waters possessing different chemical and physical 

 properties. Repetition of testr utilizing hatchery strains of fishes, other than those employed by us, might 

 also produce some variation in results. 



Many similar substances were present in the large series of compounds which we tested. The 

 aggregate data available for some groups of related chemical structures is considerable. These collective 

 data may provide clues or suggestions to investigators who are interested in the nature of any biological 

 activity which characterizes the members of a related group of substances. 



Of particular interest is the rather marked specificity seemingly displayed by certain compounds. 

 Among those tests where all three species were exposed, 264 of the substances were toxic to only one species 

 at the levels of concentration and temperature employed (included in the preceding total are the two 

 substances, omitted from this report, which merited extensive investigation as possible sea lamprey larvicides). 

 Three hundred and thirty- three additional compounds were toxic to only two species while displaying no 

 evident adverse effect upon the third. These observations are derived from the data recorded in Tables 1 and 

 2; no separate listing of these particular compounds has been prepared. 



The nature of our objectives has permitted us to do little more than note the aforementioned 

 evidences of specificity. Critical studies are required to evaluate the precise biological activity of each 

 of these substances. Many of them may prove to be of little practical value in the light of such studies; others 

 may demonstrate a useful selectivity that can find application in fish population control techniques. It is 

 hoped that the necessary further research suggested by our findings will be undertaken. 



ACKNOWLEDGMENTS 



Nearly all of the chemical samples tested by us were originally assembled for use in another 

 investigation by the staff of the USFWS Microbiological Laboratory at Leetown, West Virginia. Shortly after 

 the conclusion of their study, these samples were made available for our screening program. We are 

 indebted to Dr. S. F. Snieszko, Director of the Microbiological Laboratory, and to Dr. Robert E. Lennon and 

 Philip S. Parker for their cooperation and assistance in the transfer of sample materials, records, and related 

 correspondence. We are also grateful for their advice and suggestions concerning screening program 

 techniques. 



The investigations conducted in both laboratories would have been impossible without the 



