Effects of light spectra on the ovarian maturation and maternal immunity in the little yellow croaker (Larimichthys polyactis)

Before spawning, fish ovaries undergo multiple events to prepare for embryogenesis. Although light plays a vital role in ovarian development and neuroendocrine activities, it is unclear how it affects ovarian maturation in the little yellow croaker (Larimichthys polyactis). This study aimed to investigate the influence of different light spectra [i.e., red, blue, dark, green, white, and ambient] on the gonadosomatic index (GSI) and hepatosomatic index (HSI); histology of the ovary; vitellogenin (VTG) levels in hepatic cells; plasma 178-estradiol and growth hormone (GH) levels; total length; body weight; and innate/adaptive immune factors in captive-bred L. polyactis. The plasma 178-estradiol levels gradually decreased from Jan 8 to Apr 9, and were higher in the red, green, and blue groups than in the white, dark, and control groups. By the end of the experiment, the VTG levels were significantly higher in the red group than in the control, white, and dark groups, while those in the blue group were the lowest among the treatments. The HSI fluctuated among the groups and was higher in the control, white, and green groups on Apr 9. The proportion of oocytes at stage IV was highest in the red group, which also exhibited the best synchronization of oocyte maturation. Maternal immunoglobulin M levels were significantly higher in the red and green groups than in the control, blue, dark, and white groups at the end of the experiment, while there was no significant difference in the complement component 3 (C3) levels. Collectively, these findings demonstrate that different light spectra affect 178-estradiol secretion, VTG production, follicle synchronization and maternal immunity during ovarian maturation in L. polyactis.