THE EYES OF DEEP-SEA FISH II - FUNCTIONAL-MORPHOLOGY OF THE RETINA

Three different aspects of the morphological organisation of deep-sea fish retinae are reviewed: First, questions of general cell biological relevance are addressed with respect to the development and prolifera tion patterns of photoreceptors, and problems associated with the grow th of multibank retinae, and with outer segment renewal are discussed in situations where there is no direct contact between the retinal pig ment epithelium and the tips of rod outer segments. The second part de als with the neural portion of the deep-sea fish retina. Cell densitie s are greatly reduced, yet neurohistochemistry demonstrates that all m ajor neurotransmitters and neuropeptides found in other vertebrate ret inae are also present in deep-sea fish. Quantitatively, convergence ra tes in unspecialised parts of the retina are similar to those in noctu rnal mammals. The differentiation of horizontal cells makes it unlikel y that species with more than a single visual pigment are capable of c olour vision. In the third part. the diversity of deep-sea fish retina e is highlighted. Based on the topography of ganglion cells, species a re identified with areae or foveae located in various parts of the ret ina, giving them a greatly improved spatial resolving power in specifi c parts of their visual fields. The highest degree of specialisation i s found in tubular eyes. This is demonstrated in a case study of the s copelarchid retina, where as many as seven regions with different degr ees of differentiation can be distinguished, ranging from an area giga nto cellularis, regions with grouped rods to retinal diverticulum. (C) 1998 Elsevier Science Ltd. All rights reserved.