The retinas of seven galaxiid species collected from different habitats in Tasmania were investigated by light microscopy. There are remarkable differences between Galaxias and Paragalaxias species. The retinas of Galaxias species are characterised by a less dense retinal epithelial pigment (REP), large numbers of short and long rods, the presence of a tapetum, and stable (non-responsive) single cones in dark-adapted specimens. On the other hand, the common retinal features in Paragalaxias species include few large rods and many cones, the presence of a tapetum, lower summation and a pattern of retinomotor responses not unlike that of most other teleosts. There is no striking retinal feature that could be related to differences in their clear or turbid habitats. In spite of its probably being nocturnal, the retinal structure of P. dissimilis is basically similar to that of other diurnal Paragalaxias species. Some of the ecological constraints placed upon these species are also discussed.

The topography of Nissl-stained cells within the retinal ganglion cell layer is examined in two closely related freshwater teleosts from the family Cyprinidae. Regardless of the close phylogenetic relationship and the sympatric habitats of the two species, pronounced differences in the number and position of areas of increased cell density are observed in their retinae. in the creek chub, Semotilus atromaculatus, a midwater crepuscular feeder, three retinal specializations or areae centrales are identified in the dorsonasal, nasal, and temporal regions of the retina. In the cutlips minnow, Exoglossum maxillingua, a benthic diurnal feeder, two areae centrales are identified in temporal and nasal retina. The upper limits of the spatial resolving power of each species are calculated from the spacing of cells within the ganglion cell layer. Differences in the arrangement of isodensity contours appear to reflect the symmetry of each species' visual environment. The development and significance of up to three visually acute zones are discussed.