Gill structure of the Antarctic fishes Notothenia (Gobionotothen) gibberifrons and Trematomus newnesi, Nototheniidae stressed by salinity changes and some behavioral consequences

Abstract

In coastal Antarctic regions, melting and freezing affect water salinity. The aim of this study was to compare morphological changes of branchial epithelial cells in two species of Antarctic fishes, Notothenia (Gobionotothen) gibberifrons and Trematomus newnesi, and to detect behavioral consequences. They occur in Admiralty Bay (King George Island) during the summer, in a mean salinity of 32‰. Tests were conducted in the salinity range between 26‰ to 38‰ in experiments. Chloride cells in T. newnesi are roundish or elongated, with a small apex, at 32‰, thin with a large apex at low salinity, and roundish with small intrusions at the surface at 38‰. Chloride cells are elongated in N. (G.) gibberifrons at normal and low salinity, and increase in number, size and activity at 38‰ with large intrusions at the apical surface. In both species, mucous cells increase in volume, number and activity with salinity increase, being less active at low salinity. Epithelial detachment are observed at high salinity in T. newnesi and in low salinity in N. (G.) gibberifrons. Behavioral consequences of branchial cellular changes were observed : linear decrease of respiratory frequency with salinity increase; swimming decrease with salinity changes, except that at 26‰ forced swimming occurs and at 38‰ lethargy is interrupted by brisk jumps; paleness occurs with salinity decrease and darkness with salinity increase. These symptoms seem to be secondary consequences of hypoxia and ionic changes.