Environmental Biology of Fishes 36: 385-388, 1993. 0 1993 Kluwer Academic Publishers. Printed in the Netherlands. Retinal vascularisation in the loach Noernacheilus rupicola rupicola: coexistence of falciform process and vitreal vessels Tapas C. Nag1 & Josobanta Bhattacharjee2 Department of Zoology, University of Calcutta, 35 Ballygunge Circular Road, Calcutta 700 019, India Department of Zoology, Egerton University, P. 0. Box 536 Njoro, Kenya Received 8.1.1992 Accepted 22.8.1992 Key words: Optic disc, Hyaloid artery, Iris, Lens muscle, Accommodation Synopsis The coexistence of a fully developed falciform process and vitreal vessels, a hitherto unknown situation in teleostean intraocular vascularisation, has been noted in the loach Noernacheilus rupicola rupicola. Possible implications of this vascular development for the species have been highlighted. Introduction In teleostean eyes, retinal vascularisation at the vitreal border generally consists of a system of vit- real vessels, which are branches given off by the hyaloid artery. In some species, a pigmented vascu- lar tissue called the 'falciform process' originates from the hyaloid artery and projects through the embryonic fissure of the optic cup into the vitreous cavity (Walls 1942, Duke-Elder 1958, Hanyu 1959, 1962). Since both vitreal vessels and the falciform process appear to originate from the same source (i.e. hyaloid artery), Walls (1942) suggested that they are mutually exclusive for a given teleostean retina. This has been substantiated in several spe- cies (see e.g., Hanyu 1959, 1962, O'Connell 1963, Ali et al. 1968, Sivak & Roth 1978, Munk 1984, Kunz et al. 1985, Kunz & Callaghan 1989). Franz (1934) and later Walls (1942) suggested that vitreal vessels may nevertheless occur in association with a falciform process which is restricted to the distal end (close to ora terminalis) of the retina, project- ing rather less conspicuously into the vitreous cav- ity (the so-called low falciform process after Hany- u's classification, see Hanyu 1962). In the loach Noernacheilus rupicola rupicola (McClelland), the pattern of retinal vascularisation is different from that described for other teleosts. The coexistence of a falciform process and vitreal vessels, both fully developed, is unique with the species and has been demonstrated histologicallyin this paper. Possible implications of this vascular association are highlighted. Materials and methods Three specimens of N. rupicola rupicola (order Cypriniformes, family Cobitidae) were captured using hand nets from the stream Reshikhola, Reshi (altitude 682 m above mean sea level), South Sik- kim, India. Their standard lengths ranged from 65 to 82 mm (maximum size attained by the species = 85 mm, Day 1958). The fish were decapitated, their eyes were enucleated and fixed in Bouin's fluid for 24 h. The materials were dehydrated, infiltrated and embedded in paraffin (60" C). Serial radial sec- tions (6-7 pm thick) were stained with Harris hae- matoxylin and eosin and viewed with a Zeiss micro- scope.