Abstract

Methoxychlor (1,1,1-trichloro-2,2-bis(p-methoxyphenyl)ethane) is a chlorinated hydrocarbon pesticide that has been widely used in the United States since 1948 for a wide variety of insect pests. Previous research have shown methoxychlor to possess estrogenic or proestrogenic activity in several vertebrate and invertebrate species to include mice, salamander and sea urchin.

Two age groups of rainbow trout (Oncorhynchus mykiss) alevins (3 and 10 day post-hatch) were exposed to various concentrations and periods of exposure to field-grade methoxychlor (MXf). At 90 days post-hatch (DPH) all fry were weighed (0.1 g) and measured (fork length: mm) for growth. Our results indicate no significant differences in survival of treated fry when compared to controls. However, development, growth and sex ratios were significantly altered with exposure to MXf.

Fry exposed to MXf exhibited a significant, permanent reduction in pigmentation and severe head deformities. The occurrence of decreased pigmentation in both age groups were both concentration- and duration-responses. Presence of severe head deformities increased on a duration-response in the 3 DPH group and on concentration- and duration-responses in the 10 DPH group. Mean growth rates (length, weight and condition factor) were not significantly different between treated and control fry, however, size distribution in MXf treated fry were skewed left favoring smaller fish. Likewise, fish with decreased pigmentation were significantly smaller than their natural colored cohorts. Sex ratios were highly variable with no treatment or age group displaying a trend favoring one sex over the other, however, the presence of intersex/under-differentiated fry increased with a concentration-response.