It is reported that a large amount of melatonin can lead to testicular atrophy in hamsters . While melatonin is produced in invertebrates and has influences on the physiology and behavior, little is known about its mechanisms of action . The eyestalks of crustaceans contain the optic lobes and the x-organ/sinus gland, a neuropeptide-secreting neurohemal structure that is analogous to the vertebrate hypothalamus-pituitary system. The concentration of melatonin is high in the eyestalk of crustaceans . The removal of eyestalk induces the hypertrophy of androgenic gland and precocious spermatogenesis in nonbreeding adult males .