Branchial morphology and ion-water transport proteins in Antarctic teleosts with different modes of life

In the Antarctic Ocean salt concentration differs from the bottom to the surface owing to the seasonal forming and melting of sea ice. Antarctic teleosts present different lifestyle from benthic to pelagic. While benthic animals face a constant seawater salinity, benthic-pelagic animals have to face different salt concentration. Branchial morphology and ion-water transport proteins were compared in animals with different lifestyle. The ultrastructure of the gills was investigated by scanning electron microscopy (SEM). Na⁺/K ⁺/ATPase, Na⁺/K⁺/Cl^- cotransport protein NKCC₁ and Aquaporin 3 (AQP3), were investigated by immunohistochemistry. The immunoreactivity for the ion transporter proteins were more intense in the active benthic-pelagic animals and in the icefishes than in the sluggish benthic ones. Conversely, AQP immunoreactivity was stronger in the animals with sedentary lifestyles. The SEM showed the secondary lamellae in the benthic-pelagic animals more densely packed with the exception of the haemoglobin free teleosts.