"An Effective Quantitative Method (Node Count Method) for Evaluation of Endocrine-Disrupting Chemicals based on Secondary Sexual Characteristics of Medaka (Oryzias latipes)" 

Lin Bin-Le¹, Satoshi Hagino², Michio Kagoshima², Shouji Ashida², Akihiro Tokai¹, Kikuo Yoshida¹, Yoshitaka Yonezawa¹, Mamoru Tominaga¹, Junko Nakanishi¹

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

6th International Symposium on Environmental Endocrine Disrupters 2003 Program (Sendai, Japan 2003/12/3)

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Abstract

A more effective quantitative method for evaluation of endocrine disrupting chemicals by secondary sexual characteristics of medaka (Oryzias latipes) with S-rR strain has been developed. Although major characteristic of gross morphology in fish to detect the effects of endocrine disrupting chemicals is GSI (gonadosomatic index), some disadvantages, such as low sensitivity, are indicated. 

The node count method we proposed is simply counting number of nodes in the second ray from the last of anal fin. The S-rR strain medaka were exposed to 17 β-estradiol at three concentrations (16, 32 and 64 ng･l-1) with a period from fertilized egg to 70 days posthatch. 

At the termination of exposure, investigation on the number of nodes as well as maximum number of the small papillary processes on a ray and number of the rays with the small papillary processes were performed. 

The results showed that the number of the ray nodes would be satisfied with the purpose form the viewpoints of objectivity, accuracy, sensitivity, convenience and cost performance. In conclusion, node count method demonstrated as an effective method for detecting endocrine disruption effects on secondary sexual characteristics in medaka.

Keywords

Node Count Method, Secondary Sexual Characteristics, madaka