The gonadosomatic index, abbreviated as GSI, is the calculation of the gonad mass as a proportion of the total body mass. It is represented by the formula: GSI = [gonad weight / total tissue weight] × 100 It is a tool for measuring the sexual maturity of animals in correlation to ovary development and testes development. This index is frequently used as reporting point in OECD test guideline which may be used as indication or evidence of potential endocrine disruption effect of chemicals in regulatory frame work (EFSA and ECHA, 2017) Guidance for the identification of endocrine disruptors in the context of Regulations (EU) no 528/2012 and (EC) 1107/2009 WHO/IPCS  World Health Organisation/ International Programme for Chemical Safety , 2002 
The gonadosomatic index, abbreviated as GSI, is the calculation of the gonad mass as a proportion of the total body mass. It is represented by the formula: GSI = [gonad weight / total tissue weight] × 100 It is a tool for measuring the sexual maturity of animals in correlation to ovary development and testes development. This index is frequently used as reporting point in OECD test guideline which may be used as indication or evidence of potential endocrine disruption effect of chemicals in regulatory frame work (EFSA and ECHA, 2017) Guidance for the identification of endocrine disruptors in the context of Regulations (EU) no 528/2012 and (EC) 1107/2009 WHO/IPCS <ref name=who> World Health Organisation/ International LEAVE THE PEOPLE ALONE. , 2002 </re
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