1Training Vessel Seisui Maru, Faculty of Bioresources, Mie University, Tsu, Mie 514-8507, 2Laboratory for Fish Biology, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan
The visual accommodation system and ganglion cell distribution of the dolphin fish were examined. A well-developed lens muscle (muscles retractor lentis) was observed in the eyes. The lens muscle was composed of two muscle elements, main lens muscle and accessory lens muscle. The main lens muscle is commonly triangular in shape, however, the accessory lens muscle is a vertically-arranged rod-like component. The lens muscle nerve contains about 240 myelinated fibers. The area centralis is found in the temporal retina, the ganglion cell density is 12500 cells/mm2, and the resulting visual acuity is about 8.3 cycles/degree. The ecological significance of the well-developed accommodation system and the area centralis is discussed.