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First published online February 12, 2007
Journal of Experimental Biology 210, 815-824 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.001867

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Morphometry of retinal vasculature in Antarctic fishes is dependent upon the level of hemoglobin in circulation

Jody M. Wujcik¹, George Wang², Joseph T. Eastman³ and Bruce D. Sidell^1,*

¹ School of Marine Sciences, University of Maine, 5751 Murray Hall, Orono, ME 04469-5751, USA
² Department of Biology, University of Washington, Box 351800, Seattle, WA 98195-1800, USA
³ Department of Biomedical Sciences, Ohio University, Athens, OH 45701-2979, USA

^* Author for correspondence (e-mail: bsidell{at}maine.edu)

Accepted 3 January 2007

We quantitatively assessed ocular vascular patterns of six Antarctic notothenioid fishes that vary in their expression of the circulating oxygen-binding protein, hemoglobin (Hb). Digital image analyses revealed marked differences in vessel morphometries among notothenioid species. Hemoglobinless (–Hb) icefishes display mean vessel length densities that are greater (Chaenocephalus aceratus, 5.51±0.32 mm mm^–2; Champsocephalus gunnari, 5.15±0.50 mm mm^–2) than those observed in red-blooded (+Hb) species (Gymnodraco acuticeps, 5.20±0.46 mm mm^–2; Parachaenichthyes charcoti, 4.40±0.30 mm mm^–2; Trematomus hansoni, 3.94±0.08 mm mm^–2; Notothenia coriiceps, 2.48±0.21 mm mm^–2). –Hb fishes also have mean vessel diameters that are 1.5 times greater than vessel diameters of +Hb species (–Hb, 0.193±0.006 mm; +Hb, 0.125±0.005 mm). Vascular density index (VDI), a stereological index that is affected by both vessel number and length, is greatest in –Hb C. aceratus (3.51±0.20) and lowest in +Hb N. coriiceps (1.58±0.14). Among four +Hb species, there is a direct relationship between red blood cell content and retinal vasculature. Hematocrit (Hct) is inversely correlated to vascular density (r²=0.934) and positively correlated to intervessel distance (r²= 0.898) over a >2.3-fold range of Hct. These results indicate that anatomical capacity to supply blood to the retina increases to compensate for decreases in oxygen-carrying capacity of the blood.

Key words: Antarctic fish, hemoglobin, retina, vascular density, icefish, notothenioid, hematocrit, nitric oxide, circulation, morphometry