Effects of temperature and size on oxygen consumption and ammonia excretion by walleye

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There is a lack of information on the physiology of walleye ( Stizostedion vitreum) and, in particular, of its metabolic or excretory rate. In this study, oxygen consumption and ammonia nitrogen (NH 3-N) excretion of walleye, 75–251 mm total length (4–133 g), were measured at water temperatures of 20 ° and 25 °C. The mean weight-specific rate of oxygen consumption at 25 °C (277 mg kg −1 h −1) was significantly higher than the rate (231 mg kg −1 h −1) at 20 °C ( P < 0.001). The mean rate of ammonia excretion (19 mg kg −1 h −1) at 25 °C was higher than that (17 kg kg −1 h −1) at 20 °C ( P < 0.05). With increasing fish sizes, the weight-specific rate decreased significantly from 259 to 204 mg kg −1 h −1 at 20 °C and 340 to 228 mg kg −1 h −1 at 25 °C for oxygen consumption ( P < 0.05), and from 22 to 12 mg kg −1 h −1 at 20 °C and 29 to 9 mg kg −1 h −1 at 25 °C for ammonia excretion. The mass effect on metabolic rate can be expressed by the power of 0.82 for oxygen consumption and the power of 0.74 for ammonia nitrogen excretion. The metabolic rate of fish starved for 153 h at 20 °C was 76 mg O 2 kg −1 h −1 and endogenous excretion was 0.9 mg NH 3-N kg −1 h −1, which were 56 and 93% reductions from rates of feeding fish.