Renal corpuscle development in boreal fishes with and without antifreezes

Light and election microscopy were used to document the degree of renal corpuscle development in boreal telcost fishes that produce peptide or glycopeptide antifreeze compounds on a seasonal or permanent basis. Emphasis was placed on gadids, cottids and pleuronectids from both the North Atlantic and North Pacific Oceans. Based on the classification of Marshall and Smith (1930), corpuscle development ranged from fully glomerular (Type 1) to pauciglomerular (Type III). Unlike the situation in Antarctic notothenioid fishes, there were no aglomerular species among the boreal fishes. Corpuscles were small in diameter in gadids whereas in cottids they ranged from small to large with considerable intraspecific variation. Eight of eleven species with antifreeze had intermediate (Type II-III) or pauciglomerular kidneys with relatively few dense corpuscles (dia. 36-82μm). In some of these species an extensive mesangium and a substantial capillary endothelium contributed to a glomerular filtration barrier that was four to five times thicker than that in Type I kidneys. The corpuscles of other pauciglomerular species were unremarkable and appeared functional at the ultrastructural level. The boreal fish fauna is taxonomically diverse and, compared to the unrelated Antarctic fauna, of relatively recent evolutionary origin. Furthermore, antifreeze is present only during the winter in some species. Hence it is not surprising that the urinary conservation of antifreeze is accomplished by mechanisms other than the evolutionary loss of renal corpuscles.