Intraspecific Variation in Aerobic Metabolic Rate of Fish: Relations with Organ Size and Enzyme Activity in Brown Trout

Abstract

Highly active animals require a high aerobic capacity (i.e., a high maximum metabolic rate [MMR]) to sustain such activity, and it has been speculated that a greater capacity for aerobic performance is reflected in larger organs, which serve as energy processors but are also expensive to maintain and which increase the minimal cost of living (i.e., the basal or standard metabolic rate [SMR]). In this study, we assessed the extent of intraspecific variation in metabolic rate within a group of brown trout (Salmo trutta L.) and tested whether the observed variation in residual (body-mass-corrected) SMR, MMR, and absolute aerobic scope could be explained by variations in the residual size (mass) of metabolically active internal organs. Residual SMR was found to correlate positively with residual MMR, indicating a link between these two metabolic parameters, but no relationship between organ mass and metabolic rate was found for liver, heart, spleen, intestine, or stomach. Instead, activity in the liver of two aerobic mitochondrial enzymes, cytochrome c oxidase and, to a lesser extent, citrate synthase, was found to correlate with whole-animal metabolic rate, indicating that causes for intraspecific variation in the metabolic rate of fish can be found at a lower organizational level than organ size.

Ecological Influences and Morphological Correlates of Resting and Maximal Metabolic Rates across Teleost Fish Species

“…This variation in the proportional contribution of specific organs to metabolic rates among species could in theory damp correlations between some morphological traits and metabolic rates and play an important role in how suites of organ-level traits evolve in response to ecological pressures on whole-animal performance. This could partially explain variable findings of previous studies examining correlations between metabolic rates and organ sizes across and within species (Hayes and Garland 1995;Norin and Malte 2012;Swanson et al 2012;Zhang et al 2014). …”

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

“…Furthermore, these investigations can help to guide future research efforts and inform management targets. For example, the inter-individual variation observed in MR measurements and AAS values in the present study and in previous work (Millidine et al ., 2009; Norin and Malte, 2012; Metcalfe et al ., 2016) warrants further investigation. This variation could be due to relaxed selective pressure associated with hatchery populations, which would allow for the survival of individuals with potentially low fitness (reviewed by Reisenbichler and Rubin, 1999) and low physiological performance capabilities.…”

Intraspecific Scaling of the Resting and Maximum Metabolic Rates of the Crucian Carp (Carassius auratus)

“…Accordingly, the mass scaling exponents of metabolically active organ sizes (heart, gill, etc.) have been reported to be less than 1 in cownose rays ( Rhinoptera bonasus ), Atlantic stingrays ( Dasyatis sabina ) [27], and largemouth bronze gudgeon ( Coreius guichenoti ) [28], whereas the mass scaling exponent of metabolically active organ size was found to be not significantly different from 1 in the brown tout ( Salmo trutta ) [29]. It appears that decreases in the size of metabolically active organs as M increases may not hold for all species of fish.…”