Developmental changes in the visual acuity of red sea bream Pagrus major

Developmental changes in the visual acuity of red sea bream were investigat ed by histological examination of the retina for 61 individuals from juveni le 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 o n the eye lens diameter and the cone density on the retina. The previous st udy 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 f ound 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 200-4 00 cells/0.01 mm(2) for samples over 100 mm BL. According to the results, t he 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 leng th rather than of the cone density. The visual acuity (V.A.) was shown to f it to the allometric function of the body length (BL) as follows, V.A. = 0.00711BL(0.588), (r(2) = 0.964).