Immunocytochemical observations on pineal organ and retina of the Antarctic teleosts Pagothenia borchgrevinki and Trematomus bernacchii.

In spite of the unique conditions they have to operate under, the pineal organs of Antarctic fishes have not previously been examined. We determined immunohistochemically that in the end-vesicles and the pineal stalks of Pagothenia borchgrevinki (a species found directly beneath the sea-ice) as well as Trematomus bernacchii (a species preferring somewhat deeper water than the former) at least two populations of physiologically-different cells occurred that displayed reactions indicative of typical vertebrate photoreceptors. Comparisons with immunocytochemically treated retinal sections from the eyes of the same two species showed that anti-opsin reactivity, characteristic of rods, was particularly strong in the lumina of the pineal stalks of both species. Anti-visinin reactions stained cones in the retinal sections of both fishes and occurred throughout the pineal organs, but in particular in the end vesicles of the pineals of both species. The difference in preferred habitat depth between the two species appears to have had very little influence on both retinal and pineal immunocytochemistry. It is concluded that the pineal organs of both species, at least during the austral summer, exhibit signs of being directly photo-sensitive.