|Institution:||Mississippi State University|
|Department:||Wildlife, Fisheries & Aquaculture|
|Keywords:||oxygen consumption; spectroscopy; acidosis; hyperglycemia; respiration; tension|
|Full text PDF:||http://sun.library.msstate.edu/ETD-db/theses/available/etd-03302015-144207/|
Among the basal bony fishes, the American paddlefish ( Polyodon spathula ) has a unique respiratory strategy of ram-ventilation. However, despite the increasing problems caused by hypoxia in natural habitats occupied by this species, little information exists about their response to hypoxia. Four studies were conducted to examine the physiological and biochemical responses of juvenile paddlefish (150-181 g) to acute and chronic hypoxia. Acute hypoxia tolerance, aerobic metabolic rates and swimming capabilities of paddlefish in an intermittent respirometer or swim flume were evaluated under normoxic (partial pressures of oxygen [pO<sub>2</sub>] =140 mm Hg) and hypoxic (pO<sub>2</sub> =62 mm Hg) conditions at 18 °C and 26 °C. Additionally, blood oxygen transport, blood acid-base balance and metabolic stress were evaluated in paddlefish independently exposed to 4 different pO<sub>2</sub>s: normoxia =148 mm Hg, mild hypoxia =89 mm Hg, moderate hypoxia =59 mm Hg and extreme hypoxia =36 mm Hg, at 21°C. Blood samples were collected from paddlefish after they had been exposed to treatment pO<sub>2</sub>s for 0.25, 2, 6, 24 and 72 hours, and analyzed for hematocrit, pO<sub>2</sub>, total oxygen content, pCO<sub>2</sub>, pH, hemoglobin, Na<sup>+</sup>, K<sup>+</sup>, Ca<sup>2+</sup>, Cl<sup>-</sup>, glucose, lactate, etc. A third study used 1-D and 2-D J-resolved <sup>1</sup>H NMR to analyze metabolite changes in muscle tissue of paddlefish exposed to normoxia (148 mm Hg), or acute (0.25 h) or chronic (72 h) moderate hypoxia (59 mm Hg). The last study examined the effect of moderate hypoxia (pO<sub>2</sub>: 59 mm Hg) and subsequent recovery in normoxia (pO<sub>2</sub>: 148 mm Hg) on plasma cortisol, blood oxygen transport, blood acid-base balance, metabolic, ion-osmoregulation and enzyme parameters in paddlefish. The results indicate that paddlefish have a critical pO<sub>2</sub> of 74 mm Hg at 18 °C and 89 mm Hg at 26 °C and a lethal oxygen threshold of ~2 mg/ L. Sensitive to moderate hypoxia, death occured after 3-8 hours of extreme hypoxia. Paddlefish have reduced capacity for metabolic depression and, as a result, survival in hypoxia is limited due to a reduction in both aerobic and anaerobic (glycogen and glucose) energy stores as well as the accumulations of toxic H<sup>+</sup> and lactate. Nonetheless recovery is possible.