We report a study on the characterization of voltage-activated calcium currents (ICa) in retinal ganglion cells (RGCs) and the topographic distribution of RGCs that express different types of ICa in zebrafish retinas. In acutely isolated zebrafish RGCs, both high-voltage-activated (HVA; peak activation potential +7.4 ± 1.1 mV) and low-voltage-activated (LVA; peak activation potential –33.0 ± 1.2 mV) ICa were recorded. HVA ICa were recorded in all of the tested RGCs, whereas LVA ICa were recorded in approximately one-third of the tested cells. In RGCs that expressed both HVA and LVA ICa, the two currents were readily separated by depolarizing the cell membrane to different voltages from different holding potentials. Among RGCs that expressed LVA ICa, some cells expressed large LVA ICa (up to 130 pA), whereas others expressed small LVA ICa (approximately 20 pA). RGCs that expressed large and small LVA ICa were designated as class I and class II cells, respectively, and RGCs that expressed only HVA ICa were designated as class III cells. The topographic distribution of cell classes was similar in various areas of the retina. In the nasal-ventral retina, for example, class III cells outnumbered class I and class II cells by 10.8- and 2.6-fold, respectively. In the temporal and dorsal retinas, the density of class III cells slightly decreased, whereas the density of class I and class II cells increased. The differential expression of ICa in RGCs may correlate with the development and function of the retina. © 2006 Wiley-Liss, Inc.