IN THE BLACK-STRIPED PIPEFISH SYNGNATHUS ABASTER (TELEOSTEI, SYNGNATHIDAE) SPERMATOGENESI E STRUTTURA DEGLI SPERMATOZOI IN SYNGNATHUS ABASTER (TELEOSTEI, SYNGHATHIDAE)

The gonads of adult males of the black-striped pipefish Syngnathus abaster were observed during the reproductive season to describe mature sperm both quantitatively and qualitatively. The results show that: a) the sperms number is always very low and, does not vary significantly during the reproductive season; b) all mature sperms observed may be assigned to the introsperm-like type. These data suggest that the unique and functional sperm of Syngnathids pertain to the introsperm type typical of internally fertilizing teleostean bony fishes. Introduction - Syngnathids species, provided with a closed and highly specialized brood pouch, (such as Syngnathus and Hippocampus) are considered internal brooders, whereas those species with an open pouch or without this structure (such as Nerophis) are external brooders. Hence, in literature, it is commonly accepted that eggs fertilization of external brooders occurs in the external environment for external brooders and inside the male pouch (or marsupium) in internal brooders, but both theories have gaps. Furthemore, data on sperm morphology are limited and, in some cases, contradictory (Kvarnemo and Simmons, 2004). Therefore, histological investigation on testis morphology, spermatogenesis and sperm structure and function could significantly contribute to better understand the fertilization strategies of Syngnathids. Materials and methods - Adult males of Syngnathus abaster were collected in the Pond of Cabras (Sardinia, Italy) during the reproductive season (2007). Testes were dissected from 10 freshly killed fishes. Gonads of 2 males were fixed in Bouin's fixative, dehydrated in a graded ethanol series, cleared in toluene and embedded in paraffin. Sections (5 μm) were stained with Mallory's trichrome for observed general morphology. To examine contents of the male gonads and the number and morphology of the mature sperm fresh testes, in toto, of 9 males were gently squashed and observed with a Zeiss Axiophot light microscope.