Melatonin, a well-known antioxidant, has been widely used in sperm cryopreservation of various animals, but its regulatory mechanism in fish remains unclear. This first study on teleosts suggests a potential molecular mechanism by which melatonin may improve post-thaw sperm quality of Epinephelus fuscoguttatus via targeting mitochondrial function. Compared with the melatonin group, the MT1 receptor-inhibited group showed slightly higher sperm motility (77.09 ± 3.41% vs. 76.50 ± 1.10%), significa