Melanopsin in Lower Vertebrates: The Race Is On to Show that It Is Really There

The retina of the Antarctic teleost Trematomus bernacchii was examined immunocytochemically, using antisera against bovine rhodopsin (1:1,000) and visinin (1:250). There were no surprises with regard to rhodopsin, but positive visinin reactions occurred not only in the cones (visinin has a broad range of sensitivity to opsins), but also in some cells of the ganglion and bipolar cell layers. The reactions could be due to the presence of melanopsin or another opsin-like photopigment, but since experimental work on Antarctic fish is difficult, more accessible fish species should be examined under summer and winter conditions and different light/dark regimens. Furthermore, the search for melanopsin or similar proteins should also involve the pineal organs of lower vertebrates.