The effects of 4-tert octylphenol on the reproductive behavior of zebrafish (Danio rerio): A behavioral assay for endocrine disruptors

Advances have been made in detecting endocrine-disrupting chemicals (EDCs) using physiological or biochemical techniques, but very little has been done in the area of behavioral detection methods, perhaps because a standard methodology has not been developed. Here, I develop a behavioral assay for detecting endocrine disruptors by quantifying the effects of 4-tert octylphenol (OP), a known estrogen (E2) mimic, on the reproductive behavior of zebrafish (Danio rerio).

Fish were exposed to OP concentrations ranging from 10^7 to l0^-5.5 M dissolved in an acetone vehicle. Videotapes of male-female pairs were made for 5-min time periods under normal spawning conditions. The water was then dosed with OP, and the behavioral response was captured on videotape. To verify that the response was due to the E2-mimicking quality of OP, pairs of fish were dosed with different concentrations of E2 ranging from 10^-6 to 10^-5 M. To confirm that the response was not due to the acetone vehicle, pairs of fish were exposed to acetone only. Videotapes of male-male and female-female pairs were also recorded using 10"^ M OP following the same procedure. The Videomex V (Columbus Instruments, Columbus, Ohio), a computer-automated tracking system, was utilized to count the number of contacts and duration of each contact during social interactions of each fish pair. Analysis of covariance using the general linear model procedure, one-way analysis of variance, and left-tailed paired sample t-tests were used to analyze the data in terms of contacts and duration.

I found that OP concentrations between 10^-6 and 10^-5.5 M produced a significant decrease in both the number of contacts and the average duration of each contact in male-female pairs (p<0.05). I recorded the same significant decrease when male-female pairs were exposed to E2 concentrations between 10^-5.5 and 10^-5 M. Acetone alone did not elicit significant differences in behavior after treatment. Male-male pairs also showed a significant decline in number of contacts and duration of each contact before and after exposure to 10^-6 M OP. However, female-female pairs showed a significant decrease only in average duration of contacts at this dose. Hence, the behavioral inhibition observed for OP and E2 in the aquatic environment may not be confined to reproductive behavior.