Gonads, Spermatic Ducts, and Spermatogenesis in the Reproductive System of Male Toadfish, Opsanus tau

The testes of Opsanus tau are paired, elongated organs lying along the dorsal body wall. They are drained by a series of spermatic ducts which remain separate throughout their length and which empty their contents into the cloaca via a small genital papilla. Spermatogenesis occurs cyclically within cysts which line the testis tubules. Maturation and division occur simultaneously in all of the cells within the cyst. Six distinct stages of spermatogenesis have been recognized and described. With phase microscopy, sperm differentiation was investigated and described. Two tails are characteristic of the sperm of this species. Seasonal variations in the spermatogenic cycle occur. Animals within the same month, however, also show considerable variation. Prior to the breeding season, the tubules are filled with masses of stored sperm and the cysts are small and inactive. During the breeding season, the tubules become empty of sperm and this is rapidly followed by a reactivation of spermatogenesis with a subsequent increase in luminal spermatozoa.