Ontogeny of vision in the Antarctic fish Pagothenia borchgrevinki (Nototheniidae)

Summary Pagothenia borchgrevinki ranging in size from 63 to 245 mm were captured from beneath sea ice in McMurdo Sound by fishing and diver collection. Changes in ocular morphology with increasing body size were measured, and assessed in relation to ingested prey. Relative eye size was highest among smaller fish (<100mm total length), and declined with increasing fish size. This was accompanied by a decrease in cone density in the retina from a maximum of 14,200 mm^–2 in the smallest fish examined (63 mm), to 1000 mm^–2 in a 220 mm long fish. Theoretical acuity was lowest among fish at either end of the size range examined (minimum separable angle 40–50) but approximately constant over the remainder of the size range (25–40). Rod density also decreased with increasing body size but rod numbers per unit visual arc were relatively constant, except in the smallest fish, where angular rod density was low. The same prey taxa occurred in fish of all sizes; however, prey items smaller than about 1.5 mm were not taken by fish of any body size.