"Effect of sex-ratio on the fertility of fish using medaka (Oryzias latipes): a preliminary investigation for sex-ratio skewness in fish population exposed to endocrine disruption chemicals" 

Lin Bin-Le¹, Satoshi Hagino², Michio Kagoshima², Shouji Ashida², Akihiro Tokai¹, Junko Nakanishi¹

¹National Institute of Advanced Industrial Science and Technology
²Sumika Technoservice Corporation

SETAC 24th Annual Meeting in North America  (Austin of America 2003/11/11)

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Abstract

Skewness in the sex ratio of fish populations has been reported to be due to the adverse effects of endocrine disruption chemicals (EDCs). An evaluation of such a phenomenon from the standpoint of population-level impact is an important point to be considered. 

As a preliminary investigation towards this, we used adult medaka (Oryzias latipes) as the test fish to perform a series of reproduction experiments designed to assess the effects of different sex ratios on fecundity and fertilization rate. That is, the ratio of females to males in a series of test chambers (duplicated) was set at 10 to 1, 8 to 1, 6 to 1, 4 to 1 and 2 to 1. Experiments using the same ratios, but for male to female, were also performed.

 Endpoints associated with the population growth rate for each test chamber, such as egg number and fertilization rate, were monitored for two weeks. No significant difference in fecundity and fertility was found among the groups for sex ratios of 6 to 1, 4 to 1, and 2 to 1, while a reduction in fecundity was apparent in the groups with a sex ratio of 8 to 1 and 10 to 1. 

Although further research is still required for a quantitative evaluation of these findings, the results are expected to contribute to a qualitative understanding of sex-ratio skewness on population recruitment. 

Keywords

Endocrine disruption chemicals, Population-level impact, Ecological risk assessment, Sex-ratio, Fish