ESTIMATING METABOLIC RATE OF ELASMOBRANCHS BY MEASURING OXYGEN EXTRACTION AT THE GILLS
University of Delaware
Metabolism is the series of chemical reactions that convert food into energy, influencing all aspects of an organism’s biology. Oxygen is a key substrate used in metabolism and therefore, rates of oxygen consumption are used as a proxy for metabolic rates. We placed fiber optic oxygen sensors at the gills of two shark species: Carcharhinus plumbeus (sandbar shark) and Mustelus canis (smooth dogfish shark) to measure oxygen content in the gills. Elasmobranchs were anesthetized using MS-222, and an oxygen probe was placed at specific locations along all five gills to measure the spatial variability in oxygen content of gill exhalant. The differential values in oxygen content between ambient water and the gill exhalant were used to estimate the degree of oxygen extraction at the gills. We found significant differences (Two factor ANOVA, P < 0.05) in the oxygen content of gill exhalant between gills and the second and third gills were the most efficient for oxygen extraction. We then tested for the effect that water flow rate (mL/s) had on the oxygen content of gill exhalant and used these flow rates to calculate the metabolic rate of a C. plumbeus individual. The efficiency of oxygen extraction varied by the activity level of the species, with more active species such as C. plumbeus being able to extract oxygen more efficiently than sluggish, demersal species like M. canis. This experiment was the first step to calculating the metabolic rates of freely swimming elasmobranchs and fishes in the wild.
environmental science, elasmobranchs, gills