The structures of the kidncys and urinary bladders of four Antarctic teleosts, Pagothenia borchgrevinki, Trematomus bernacchii, Trematomus hansoni and Austrolycichthys brachycephalus, were compared by light microscopy. The kidney of A. brachycephalus is glomerular; the other three species studied have aglomerular kidneys.
The epithelium of urinary bladder in P. borchgrevinki and T, bernacchii, is composed of colum-nar cells in the areas near the collecting tubule but gradually changes to cuboidal cells which line most of the bladder. The entire bladder epithelium of T. hansoni is composed of simple cuboidal cells while the bladder epithelium of A. brachycephalus shows intermediate type between the other two groups.
These morphological differences in urinary bladder epithelia of Antarctic teleosts may reflect adaptations to diluted sea water during the thawing season.