Testicular structure and spawning cycle in the silvery croaker, Otolithes ruber (Perciformes: Sciaenidae) in the Kuwaiti waters of the Arabian Gulf

Abstract

The structure of the testes and maturity stages in the male silvery croaker, Otolithes ruber were investigated from March 1999 to March 2000. Based on the location of spermatogonia within the germinal epithelium, the testis structure is classified as the “unrestricted spermatogonial” testicular type. Germ cells proliferate through mitotic divisions of spermatogonia, giving rise to primary and secondary spermatocytes, which through meiotic divisions transform into spermatids. As spermatogenesis progresses, an elongation of the testicular lobules takes place. During final spermiogenesis, spermatids are arranged in clusters, with heads in one direction and tails in the opposite. Spermatozoa are then liberated from these structures into the lobula lumina. The testicular lobules further elongate, and many of them form a continuum within the germinal epithelium, extending toward the periphery. The walls of the other lobules fuse, producing anastomosing sperm-filled lobular compartments. A main sperm duct is formed into which spermatozoa from the lobules are voided. A time lapse between sexual maturity and onset of spawning was observed, thus supporting the existing view that the anastomosing compartments are used for sperm storage during the latter part of the maturation process. Six maturity stages of the testis are delineated during the annual reproductive cycle based on macroscopic and histological characteristics. Results show that male O. ruber spawns from March through April in Kuwaiti waters.