Developmental Changes in the Visual Acuity of Red Sea Bream Pagrus major

Abstract

Developmental changes in the visual acuity of red sea bream were investigated by histological examination of the retina for 61 individuals from juvenile to adult stage (BL 23-609 mm). The highest cone density could be located in the dorso-temporal area of the retina. The visual acuity depends both on the eye lens diameter and the cone density on the retina. The previous study reported that the minimum separable angle is obviously greater than the resolving power of the lens. The lens diameter increased from 1.3 mm to 11.8 mm proportionally with the growth of body length. The cone density was found to fit in an exponentially declining curve, where it steeply decreases in the range of 23-100 mm BL and becomes a gentle slope to be around 200-400 cells/0.01 mm2 for samples over 100 mm BL. According to the results, the visual acuity was increased with growth; from 0.05 for 23 mm BL to 0.28 for 504 mm BL specimen. The improvement of acuity can be attributed increase of the lens focal length rather than of the cone density. The visual acuity (V.A.) was shown to fit to the allometric function of the body length (BL) as follows, V.A.=0.00711BL0.588, (r2=0.964).