FINE-STRUCTURE OF THE CHORION AND MICROPYLE OF THE SEA BASS EGG DICENTRARCHUS-LABRAX (TELEOSTEA, PERCICHTHYDAE)

The fine structure of the chorion and micropyle of mature unfertilized eggs of the sea bass Dicentrarchus labrax was examined by scanning an d transmission electron microscopy. The chorion consists of three laye rs: a thin electrondense outer layer, a paracrystalline middle layer a nd a thick inner layer consisting of 12 electrondense filamentous lame llae alternating with interlamellar material of lower electrondensity. The two more external layers are crossed by pore canals opening on th e egg surface. The funnel-type micropyle is located at the animal pole of the egg. The walls of the micropylar canal have circular, rib-like thickenings reflecting the stratified inner layer of the chorion. The results are discussed and compared with those in other Teleostea.