Reproductively mature koi carps (Cyprinus carpio) showed a prominent diurnal variation of sex steroids with sustained nocturnal rise. Exposure to chronic hypoxia (DO < 0.8 mg/l) disrupted nocturnal sex steroid production in koi carp gonads. Inhibition of sex steroidogenesis is linked to the down-regulation of HMG-Co A reductase (p < 0.05), which acts as a rate-limiting enzyme in the mevalonate pathway for cholesterol production. HMG-CoA reductase inhibition was obvious in the gonads and liver of both sexes during 18.00 h and 21.00 h resulting in hypocholesterolemia (p < 0.05). The levels of sex steroids, such as estradiol, testosterone, and 11-keto-testosterone in gonads were depleted below the optimum levels owing to disruption of de novo cholesterol synthesis along with attenuation of HDL-cholesterol level in serum. Inhibition of melatonin under hypoxic conditions indicates disruption of melatonin effects on the hypothalamus-pituitary-gonadal (HPG) axis of koi carp. Under severe hypoxic stress, koi carp promoted energy conservation by switching over to the triglyceride (TGA) pathway instead of the mevalonate pathway to suppress cholesterol production. Chronic hypoxia inhibited cholesterol synthesis, a prerequisite for gonadal maturation. It promoted TGA production, as an alternative energy source, suggesting a probable mitigation strategy adopted by hypoxia-tolerant fish to deal with low dissolved oxygen frequently occurring in aquatic bodies.

繁殖成熟的锦鲤（Cyprinus carpio）表现出明显的性类固醇昼夜变化，夜间持续上升。暴露于慢性缺氧（DO <0.8 mg / l）会破坏锦鲤性腺的夜间性类固醇生成。性类固醇生成的抑制与HMG-Co A还原酶的下调有关（p  <0.05），HMG-Co A还原酶是甲羟戊酸途径中胆固醇生成的限速酶。HMG-CoA还原酶抑制作用在男女性腺和肝中均在18.00 h和21.00 h期间明显发生，导致低胆固醇血症（p <0.05）。性腺中的性类固醇，例如雌二醇，睾丸激素和11-酮-睾丸激素的水平低于最佳水平，这是由于从头胆固醇合成受到破坏以及血清HDL-胆固醇水平下降所致。在低氧条件下抑制褪黑激素表明褪黑激素对锦鲤下丘脑-垂体-性腺（HPG）轴的影响。在严重的低氧胁迫下，锦鲤通过切换到甘油三酸酯（TGA）途径而不是甲羟戊酸途径来抑制胆固醇的产生，从而促进了能量的节约。慢性缺氧会抑制胆固醇合成，这是性腺成熟的先决条件。作为替代能源，它促进了TGA的生产，