This study aimed to assess the effect of Tribulus terrestris extract as a feed additive containing phytoandrogens on the reproductive parameters of common carp. This experiment employed a completely randomized design with four treatments and three replications. A total of 120 healthy C. carpio (63.8±0.4 g) were randomized into 12 experimental groups and fed a standard carp diet containing 0, 100, 1000, and 2,000 mg/kg of T. terrestris extract for 60 days. The results demonstrated that T. terrestris significantly increased testosterone secretion (P>0.05), whereas estradiol secretion decreased dramatically (P>0.05). We found that GSI increased in 100 and 1000 mg/kg treatments relative to the control, but this increase was not statistically significant (P>0.05). However, this index decreased significantly in fish fed 2,000 mg/kg extract. The GSI of female carp increased significantly after 2000 mg/kg treatment (P>0.05). According to the results, T. terrestris extract exhibited the greatest androgenic effect at 100 mg/kg, whereas an excess extract had the opposite effect on the male carp.

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