Retinal topography of ganglion cells in immature ocean sunfish, Mola mola

Abstract

The ocean sunfish, Mola mola, is the largest known bony fish. Based on prior studies of diet composition, it is considered to be a pelagic zooplanktivore. However, a recent study using acoustic telemetry revealed that they repeatedly dive to depths of >50 m during the day. We examined the distribution of cells within the retinal ganglion cell layer in the immature ocean sunfish (c.a. 50 cm total length) and estimated their visual acuity with respect to the main visual axis and visual fields. Visual acuity was between 3.37 and 4.41 cycles/degree. The region of highest cell density was located in the dorsotemporal retina, indicating that the main visual axis of ocean sunfish is directed towards the lower frontal portion of the visual field. This axis is considered beneficial for detecting prey items when the sunfish are migrating vertically through the water column, and in foraging behavior near the sea bottom.

The biology and ecology of the ocean sunfish Mola mola: a review of current knowledge and future research perspectives

“…Such eye movements, especially in the ventral plane, were documented in live specimens by Kino et al (2009). Visual acuity, calculated from peak ganglion cell densities, was between 3.51 and 4.33 cycles per degree, comparable to adult sharks (2.8-3.7 cycles per degree; Kino et al 2009) but much lower than adult blue marlin, Makaira nigricans (8.5 cycles per degree; Fritsches et al 2003). It should be noted, however, that these were very small ocean sunfish and visual acuity typically increases as fish grow (Fritsches et al 2003).…”

“…A recent study by Kino et al (2009) investigated the eyes of three immature M. mola from Japanese waters. They found a region of high retinal ganglion cell density that implied a main visual axis directed towards the lower frontal portion of the visual field (10-20°below horizontal; Kino et al 2009).…”

“…They found a region of high retinal ganglion cell density that implied a main visual axis directed towards the lower frontal portion of the visual field (10-20°below horizontal; Kino et al 2009). Highdensity areas are indicative of a well-developed visual system and also require the ability to move the eye to direct this region of more acute vision to objects of interest (Fritsches et al 2003).…”

“…Highdensity areas are indicative of a well-developed visual system and also require the ability to move the eye to direct this region of more acute vision to objects of interest (Fritsches et al 2003). Such eye movements, especially in the ventral plane, were documented in live specimens by Kino et al (2009). Visual acuity, calculated from peak ganglion cell densities, was between 3.51 and 4.33 cycles per degree, comparable to adult sharks (2.8-3.7 cycles per degree; Kino et al 2009) but much lower than adult blue marlin, Makaira nigricans (8.5 cycles per degree; Fritsches et al 2003).…”

Comparison of functional and anatomical estimations of visual acuity in two species of coral reef fish

“…Species found inhabiting open water can have much larger differences in acuity (for example, Lethrinus chrysostomus and Gymnocranuis bitorquatus: 19 and 27 cycles deg −1 , respectively) (Collin and Pettigrew, 1989). The visual acuity of fish has been measured using a range of behavioural (Brunner, 1934;Yamanouchi, 1956;Nakamura, 1968;Hodos and Yolen, 1976;Hairston et al, 1982;Neave, 1984;Pankhurst et al, 1993;Neumeyer, 2003b;Haug et al, 2010;Lee and O'Brian, 2011;Champ, 2012) and anatomical methods (Hodos and Yolen, 1976;Collin and Pettigrew, 1989;Fritsches et al, 2003;Matsuda et al, 2005Matsuda et al, , 2008Theiss et al, 2007;Litherland and Collin, 2008;Kino et al, 2009;Carton and Vaughan, 2010;Temple et al, 2010;Lee and O'Brian, 2011;Champ, 2012). However, because of the many differences in methodology, comparisons between studies are difficult.…”