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

In the Antarctic Ocean salt concentration diVers from the bottom to the surface owing to the seasonal form- ing and melting of sea ice. Antarctic teleosts present diVer- ent lifestyle from benthic to pelagic. While benthic animals face a constant seawater salinity, benthic–pelagic animals have to face diVerent salt concentration. Branchial mor- phology and ion–water transport proteins were compared in animals with diVerent lifestyle. The ultrastructure of the gills was investigated by scanning electron microscopy (SEM). Na+/K+/A TPase, 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 ben- thic–pelagic animals and in the iceWshes than in the slug- gish benthic ones. Conversely, AQP immunoreactivity was stronger in the animals with sedentary lifestyles. The SEM showed the secondary lamellae in the benthic–pelagic ani- mals more densely packed with the exception of the haemo- globin free teleosts.