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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
Morphometry of retinal vasculature in Antarctic fishes is dependent upon the level of hemoglobin in circulation
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
mm2; Champsocephalus gunnari, 5.15±0.50 mm
mm2) than those observed in red-blooded (+Hb) species
(Gymnodraco acuticeps, 5.20±0.46 mm mm2;
Parachaenichthyes charcoti, 4.40±0.30 mm
mm2; Trematomus hansoni, 3.94±0.08 mm
mm2; Notothenia coriiceps, 2.48±0.21 mm
mm2). 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