Measurement and relevance of maximum metabolic rate in fishes

Abstract

Maximum (aerobic) metabolic rate (MMR) is defined here as the maximum rate of oxygen consumption (ṀO 2max ) that a fish can achieve at a given temperature under any ecologically relevant circumstance. Different techniques exist for eliciting MMR of fishes, of which swim-flume respirometry (critical swimming speed tests and burst-swimming protocols) and exhaustive chases are the most common. Available data suggest that the most suitable method for eliciting MMR varies with species and ecotype, and depends on the propensity of the fish to sustain swimming for extended durations as well as its capacity to simultaneously exercise and digest food. MMR varies substantially (>10 fold) between species with different lifestyles (i.e. interspecific variation), and to a lesser extent (<three-fold) between individuals of the same species (i.e. intraspecific variation). MMR often changes allometrically with body size and is modulated by several environmental factors, including temperature and oxygen availability. Due to the significance of MMR in determining aerobic scope, interest in measuring this trait has spread across disciplines in attempts to predict effects of climate change on fish populations. Here, various techniques used to elicit and measure MMR in different fish species with contrasting lifestyles are outlined and the relevance of MMR to the ecology, fitness and climate change resilience of fishes is discussed.

Unusual aerobic performance at high temperatures in juvenile Chinook salmon,Oncorhynchus tshawytscha

“…two to six burst swims) until the fish became exhausted. Norin and Clark (2016) suggest that the peak MR of an exhausted fish is a reliable estimate of MMR. Again, exhausted fish were allowed to recover in RMR conditions for at least 1 h.…”

High thermal tolerance of a rainbow trout population near its southern range limit suggests local thermal adjustment

“…Critical swimming velocity and burst swimming protocols (Reidy et al ., 1995; Killen et al ., 2007; Clark et al ., 2013; Norin and Clark, 2016) were used to determine MMR. They began between 08.00 and 09.00 h and lasted 2–6 h. For the critical swimming velocity test, water velocity was gradually increased until the fish continuously swam at 30 cm s −1 for 20 min.…”

Acclimation potential of Arctic cod (Boreogadus saida Lepechin) from the rapidly warming Arctic Ocean

“…Then, the fish was removed from the respirometer and placed in a ∼12 litre circular tank containing aerated water at the test temperature for exhaustive exercise. Chasing involved a 5 min period of hand chasing, gentle tail pinches and lifting until unresponsive to touch, followed by brief air exposure (Norin and Clark, 2016). The fish was returned to the respirometer and oxygen uptake measurement resumed within 30 s and continued over 5-30 min, depending on the test temperature.…”