Results of bioassays and gas chromatographic analyses show that mosquitofish, Gambusia affinis, from near heavily-treated cotton fields near Belzoni, Mississippi (36-hr TLm= 1,000 ppb) and from an uncontaminated site near State College, Mississippi (36-hr TLm= 1 ppb) remove endrin from static test solutions at the same rate. A 500 ppb endrin solution produced 32 mortality in 50 susceptible fish in 25 min but required 144 hr in resistant fish. Relative mortality of fed and starved fish in endrin solutions and the rate of endrin uptake discount swallowing as the primary pathway of endrin entry into mosquitofish. About six times as much endrin is taken up via the exposed head region as is taken up by the general body surfaces. Oxygen requirements of the two populations are similar, but increase for susceptible fish at low endrin concentrations and for resistant fish at high concentrations coincident with the appearance of symptoms of endrin poisoning.
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