Effects of Pesticides 



Edward Chin 



Tests of pesticides on estuarine species were continued this year, 

 with emphasis on the commercieilly important penaeid shrimps in Galveston 

 Bay. The relative toxicity of various chlorinated hydrocarbons to brown 

 shrimp, Penaeus aztecus, and white shrimp, P. setiferus, is shown in the 

 table following. The index of relative toxicity adopted is the median tolerance 

 limit (TLrn) which is the concentration at which 50 percent of the test animals 

 are able to survive for a specified period of exposure. Except for the results 

 using postlarval Crustacea, the TLjn values are based on tests conducted in 

 100 liters of medivun in disposable polyethylene bags. Because of their small 

 size and cannibalistic tendencies, postlarval crabs and shrimps were tested 

 individually in 250-ml. glass vessels. Methods were described in greater de- 

 tail in last year's annual report. 









.^> 



Testing toxicity of pesticides on postlarval shrimp contained individually 



in 250-cc. reagent bottles. 



49 



