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 and transmission electron microscopy. The chorion consists of three layers: a thin electrondense outer layer, a paracrystalline middle layer and a thick inner layer consisting of 12 electrondense filamentous lamellae alternating with interlamellar material of lower electrondensity. The two more external layers are crossed by pore canals opening on the 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.