Acceleration of ovarian degeneration by salinity stress is mediated at multiple levels of the hypothalamic-pituitary-gonadal axis and the liver in spotted scat (Scatophagus argus)

The spotted scat ( Scatophagus argus ) is a coastal fish and that lives in a wide range of salinities. Environmental salinity can affect the reproduction of spotted scat. However, the exact effects of environmental salinity fluctuations on the reproductive regulation in teleosts at the HPG axis and the liver levels remain unclear. Therefore, changes in the gonadosomatic index (GSI) and serum 17β-estradiol (E 2 ) levels were measured after 20 days of exposure to salinities of 5 ppt (low salinity group, LS), 25 ppt (control group, Ctrl), and 35 ppt (high salinity group, HS) in female spotted scat. The expression of genes associated with reproductive regulation in the hypothalamus ( sbgnrh and sgnrh ), pituitary ( fshβ and lhβ ), and ovary ( fshr and lhr ) was examined. In addition, the genes associated with steroidogenesis and vitellogenesis in the ovary and in the liver were also investigated. The results showed that the GSI decreased significantly, and oocyte degeneration was accelerated with low- and high-salinity stress. ELISA revealed no significant change in estradiol (E 2 ) levels in the LS and HS groups. qRT-PCR showed a significant decrease in sbgnrh and lhr in the HS group, and in lhβ and lhr in the LS group. However, sgnrh , fshβ, and fshr did not change in either group. Genes associated with steroidogenesis, such as star1 , cyp17a1 , cyp17a2 , and hsd3b1 , decreased significantly after acclimation to low and high salinity, however, hsd17b14 was increased. Vitellogenesis-associated genes, such as estrogen receptors ( erα and erβ2 ) in the ovary, decreased, while vitellogenin ( vtgAa , vtgAb , and vtgc ) increased in the liver. These results suggest that environmental salinity stress profoundly affects the reproductive physiology of spotted scat by disrupting the HPG axis signaling, steroidogenic pathways, and vitellogenesis. This paper provides a comprehensive insight into the impact of environmental salinity stress on reproductive regulation in spotted scat. • Both low and high salinity stress reduced the GSI and accelerated oocyte degeneration in the spotted scat. • HPG signaling was disrupted by reducing sbgnrh and lhr in high, and lhβ and lhr in low salinity stress. • Steroidogenesis was impaired under both salinity stress conditions due to downregulation of star1 , cyp17a1/a2 , and hsd3b1 . • Vitellogenesis was decreased in the ovary but accelerated in the liver in both low- and high-salinity environments.