Effects of Dietary Cholesterol Regulation on Spermatogenesis of Gobiocypris rarus Rare Minnow

Cholesterol is an important component of cell membranes, and also a precursor for the synthesis of sex hormones, playing an important role in reproduction. However, few studies have focused on cholesterol and reproductive health. To investigate the toxic effects of different cholesterol levels on the spermatogenesis of rare minnows, we regulate the cholesterol content in fish by feeding them a high-cholesterol diet and cholesterol inhibitor pravastatin, and cholesterol levels, sex hormone (T and 11KT) levels, testis histology, sperm morphology and function, and the expression of genes related to sex hormone synthesis were investigated. The research findings indicate that increasing cholesterol levels significantly increases the liver weight and hepatic–somatic index, as well as the total cholesterol and free cholesterol levels in the testis, liver, and plasma of rare minnow, while inhibiting cholesterol has the opposite effect (p < 0.05). However, both increasing and decreasing cholesterol levels can suppress rare minnow testicular development, as evidenced by a decrease in testis weight, lowered gonadosomatic index, suppressed sex hormone levels, and reduced mature sperm count. Further exploration revealed that the expression of sex hormone synthesis-related genes, including star, cyp19a1a, and hsd11b2, was significantly affected (p < 0.05), which may be an important reason for the decrease in sex hormone synthesis and consequent inhibition of testicular development. At the same time, the fertilization ability of mature sperm in both treatment groups significantly decreased. Scanning electron microscopy and fluorescence polarization tests showed that reducing cholesterol levels significantly increased the rate of sperm head cell membrane damage, while both increasing and decreasing cholesterol levels led to a reduction in sperm cell membrane fluidity, which may be the main reason for the decrease in sperm fertilization ability. This study demonstrates that both increasing and decreasing the levels of cholesterol are detrimental to the fish spermatogenesis, providing fundamental information for the study of fish reproduction and also a reference for the causes of male reproductive dysfunction.