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 or gans of Antarctic fishes have not previously been examined. We determined i mmunohistochemically that in the end-vesicles and the pineal stalks of Pago thenia 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 occ urred that displayed reactions indicative of typical vertebrate photorecept ors. Comparisons with immunocytochemically treated retinal sections from th e eyes of the same two species showed that anti-opsin reactivity, character istic of rods, was particularly strong in the lumina of the pineal stalks o f both species. Anti-visinin reactions stained cones in the retinal section s of both fishes and occurred throughout the pineal organs, but in particul ar in the end vesicles of the pineals of both species. The difference in pr eferred habitat depth between the two species appears to have had very litt le influence on both retinal and pineal immunocytochemistry. It is conclude d that the pineal organs of both species, at least during the austral summe r, exhibit signs of being directly photo-sensitive.