Fine Structure of the Egg Membranes in Four Species of Pleuronectinae

Abstract

The eggs of four species of closely related pleuronectine fishes were examined by scanning electron microscope to elucidate the significance of their different membrane structures. Hippoglossoides dubius lays pelagic egg with a wide perivitelline space. The egg membrane of this species was thinnest among the four species examined, consisting of a simple lamellar structure. In contrast, Pleuronectes yokohamae lays demersal eggs with a narrow perivitelline space. The egg membrane of this species was thicker and composed of a much more complex lamellar structure than those of the other species. Eopseta grigorjewi and Pleuronichthys cornutus eggs, with the membranes of medium thicknesses and lamellar structures between the former two species, are pelagic with a narrow perivitelline spaces, P. cornutus showed ornamentation consisted regular hexagonally-arranged walls on the egg membrane surface. With respect to pores on the egg membrane, all the pleuronectine eggs examined in this study had larger pore diameters and lower pore densities than in other teleost species reported thus far. It is likely that the membrane thickness, lamellar structure and surface sculpturing of the eggs are closely related to environmental factors, whereas the pore diameter and pore density reflect systematic relationships.