Chronic Carbonate Alkalinity Exposure Induces Dysfunction in Ovary and Testis Development in Largemouth Bass...

Saline-alkaline water resources are globally widespread, and their rational development offers significant potential to alleviate freshwater scarcity. Saline-alkaline water aquaculture farming not only affects fish growth and survival but also impairs reproductive and developmental functions. Largemouth bass (Micropterus salmoides), an economically important fish, has demonstrated excellent high tolerance to such environments, in order to investigate the effects of alkaline water aquaculture environments on its growth performance, sex hormone levels, gonadal development, and molecular adaptation mechanisms. In this study, largemouth bass were chronically exposed to freshwater (0.55 mmol/L), low alkalinity (10 mmol/L), or high alkalinity (25 mmol/L) and cultured for 80 days. Alkalinity exposure more severely impacted the growth rate of females. High alkalinity significantly increased the hepatosomatic index and decreased the gonadosomatic index in both sexes; moreover, it induced oxidative stress in both sexes, evidenced by reduced superoxide dismutase (SOD), catalase (CAT), and total antioxidant capacity (TAOC) levels and elevated malondialdehyde (MDA) content. Furthermore, the levels of sex hormones Serum estradiol (E2), 11-ketotestosterone (11-KT), and testosterone were significantly reduced, accompanied by either an elevated ratio of primary oocytes and follicular atresia, or by reduced spermatogenesis. Apoptotic signals appeared in gonadal interstitial cells, with upregulated expression of genes P53, Bax, Casp3, and Casp8. Ultrastructural damage included fewer mitochondria and cristae blurring, further indicating tissue damage causing dysfunction. Transcriptome results showed that oxidative stress damage and energy metabolism imbalance caused by carbonate alkalinity were key to the delayed gonadal development, which was mainly manifested in enrichment of the ECM-receptor interaction and PI3K-Akt signaling pathways in females exposed to low alkalinity, and the GnRH secretion and chemokine signaling pathways in males. Glycosphingolipid biosynthesis and Ferroptosis pathway were enriched in females exposed to high alkalinity, and the Cortisol synthesis and secretion pathway were enriched in males. Overall, high-alkalinity exposure significantly delayed gonadal development in both sexes of largemouth bass, leading to reproductive impairment.