Edema formation and impaired O2 transfer in ringer‐perfused gills of the eel, Anguilla australis

Isolated gills of the eel (Anguilla australis) were perfused with various solutions and subsequently examined using light or scanning electron microscopy. Oxygen transfer was measured in some perfusions. Ringer perfusion impaired O2 transfer and caused irreversible structural damage to the gills. Severe edema was consistently observed as a massive enlargement of the secondary lamellar subepithelial space. Addition of plasma protein substitutes (1–8% polyvinylpyrrolidone; 2–3% dextran) to Ringer perfusates failed to prevent edema, even when used in combination with 0.2% bovine serum albumin. Perfusion with fresh mammalian blood or plasma for up to 30 min did not cause edema, plasma perfusion significantly improving O2 transfer. Unless autologous blood or plasma is available, mammalian plasma is the most suitable perfusate for exchange studies in fish gills. As yet unidentified proteins in plasma probably reduce the pore dimensions of the pillar cell flanges, thereby reducing colloid loss from the vascular space.