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TAKE MY BREATH AWAY... PHYSIOLOGICAL RESPONSES OF ATLANTIC STINGRAYS, DASYATIS SABINA, TO CYCLING HYPOXIA
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TAKE MY BREATH AWAY... PHYSIOLOGICAL RESPONSES OF ATLANTIC STINGRAYS, DASYATIS SABINA, TO CYCLING HYPOXIA

Theresa Francine Dabruzzi
University of West Florida
Master of Science (MS), University of West Florida
2013

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Abstract

Atlantic stingrays, Dasyatis sabina, inhabit shallow water seagrass habitats where they experience temperature and salinity fluctuations, as well as natural cycles of hypoxia. In this study I examined changes in gill morphology, critical oxygen minimum, and hemoglobin/hematocrit levels in Atlantic stingrays acclimated for 20 days at normoxia (.5.50 mg/l), or normoxia with 6 hour intervals of moderate (4.0 mg/l), or marked hypoxia (2.0 mg/l). Neither hematocrit (Range 7.3-7.6 g/dl) nor hemoglobin (Range 24.3-26.7%) mean values differed significantly across treatments. Perhaps the existing hemoglobin is sufficient, or stingrays have switched to a more efficient isoform. Gill dimensions including number of primary filaments, primary filament length, and number of secondary lamellae show increasing trends with severity of hypoxic exposure. Mass specific gill surface areas ranged between 85 and 140 mm2/g, and showed a significant 1.7 fold increase in total surface area between the normoxic and markedly hypoxic treatment group. Fish in the normoxic group had significantly higher critical oxygen minima (0.67±0.11 mg/l) than stingrays in either hypoxic treatment (0.40±0.05, and 0.42±0.06 mg/l). Gill remodeling improves hypoxia tolerance and likely allows Atlantic stingrays to successfully exploit hypoxic habitats inaccessible to predators and competitors, as well as forage across a wider habitat range.
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