The reproductive cycle of the endangered cyprinid Alburnus albidus: morphological changes of the gonads and plasma sex steroid fluctuations

Alburnus albidus is an endangered and little known cyprinid fish species en demic in southern Italy. Histological characteristics of testes of A. albid us from River Alento, Campania Region, were analysed every month between Ja nuary-July 1996. Depending on the relative abundance of spermatogonia, sper matocytes, spermatides and spermatozoa in the testes, we divided the gonada l cycle into four stages: 1. quiescence, when mainly spermatogonia were pre sent (January-February); 2. recrudescence, when spermatocytes were abundant , although spermatids were also detectable (March-April); 3. spawning, when cysts contained all stages of germ cells (May-June); 4. Postspawning, when testes contained spermatogonia only (July). The concentration of sex stero ids (androgens, 17 alpha-hydroxyprogesterone and 17 beta-estradiol) fluctua ted throughout the year. Androgen levels were high during the quiescence an d the spawning periods. 17 beta-hydroxyprogesterone concentration showed a sharp increase just before the spawning period. 17 beta-estradiol levels we re quite low, with the exception of a slight increase during the recrudesce nce and the spawning periods.