Re-examination of the spermatozoal ultrastructure of eels: observations ofthe external morphology of spermatozoa in three species

The nucleus of the spermatozoa in both Anguilla anguilla and A. japonica sp ecies is asymmetric on the longitudinal axis, being gently curved and elong ated with a hook-shaped superior end directed inside the crescent. A single spherical mitochondrion is located at the superoanterior portion of the nu cleus. Nine striae extending from the basal portion of the flagellum run al ong the right side of nuclear surface. These are always oriented toward the mitochondrial portion and their ends are located on the mitochondrion. The se features are seen not only in both Anguilla species but also in Muraenes ox cinereus and in other species including other genera of Anguilliformes. It is suggested that these features be considered as common to Anguilliform es. (C) 2000 The Fisheries Society of the British Isles.