The presentstudyinvestigatedthehormonesconcentrationsandgonadsalterationsof Clarias gariepinus caused bysublethelconcentrationsof4-nonylphenol(0,0.05,0.08and0.1mg/l).The changesintheactivitiesofthehormonesafterexposuretothesesubletheldosesof4-nonylpenol referredtoendocrinedisruptionin Clariasgariepinus in associationwithhistopathologicalchangesin reproductivetissues.Thelevelsofthyroidstimulatinghormone(TSH),triiodothyronine(T3),total thyroxine(T4),folliclestimulatinghormone(FSH),luteinizinghormone(LH)andtestosterone concentrationssignificantlydecreased(Po0.05) inthetreatedfishincomparisonwithcontrol.17-bestradiolincreasedsignificantly( Po0.05) with4-nonylphenolconcentrationsincrease.Reductionin the gonadosomaticindexwasevidentwithincreaseofsublethaldosesof4-nonylphenol.The histopathologicalchangesofNP-treatedwererecordedingonadsof Clariasgariepinus reflectingtheir sensitivitytoNP-estrogeniclikeeffects.