The eggs of the freshwater fish Epiplatys dageti have tight plasma membranes without intramembranous particles.

The plasma membrane of fish (Epiplatys dageti) eggs, which are capable of developing in salt-free water despite intracellular osmolarity corresponding to a pressure gradient of 7 to 8 atmospheres, is almost devoid of intramembrane particles. The specific membrane resistance is at least 3 orders of magnitude larger than that of nerve or muscle cells of different species indicating that the membrane is tight. These findings support the view that intramembranous particles are involved in transmembrane transport of ions, and indicate that the ionic concentration gradient in this cell is maintained by a tight membrane rather than by active transport.