Higher Maximum Metabolic Rates Research Articles

Metabolic scope and swimming performance of juvenile channel (Ictalurus punctatus), blue (I. furcatus), and hybrid (I. punctatus × I. furcatus) catfish at moderate and high temperatures

Despite the growing use of hybrid catfish (Ictalurus punctatus × I. furcatus) in the aquaculture industry, few studies have compared their physiological performance with more commonly reared channel catfish (I. punctatus) and their other parent stock, blue catfish (I. furcatus). An understanding of metabolic scope and swimming performance, particularly in elevated water temperatures, is important because these metrics directly relate to the overall performance or fitness of an organism. Therefore, metabolic scope, the difference between standard metabolic rate (SMR) and maximum metabolic rate (MMR), and swimming performance in channel, blue, and hybrid catfish were compared using intermittent and swim-flume respirometry coupled with Ucrit protocols at moderate (23 °C) and high (33 °C) temperatures. It was hypothesized hybrid catfish would have larger metabolic scope and greater swimming performance than channel and blue catfish due to heterosis from hybridization. Hybrid catfish SMR did not differ from blue catfish, while hybrid catfish had higher MMR, larger metabolic scope, and better swimming performance than channel and blue catfish. These results indicate hybrid catfish outperform channel and blue catfish, in terms of swimming performance, presumably due to larger metabolic scope over moderate to high temperatures.

Metabolism, population growth, and the fast‐slow life history continuum of marine fishes

AbstractThe maximum intrinsic rate of population increase (rmax) represents a population's maximum capacity to replace itself and is central to fisheries management and conservation. Species with lower rmax typically have slower life histories compared to species with faster life histories and higher rmax. Here, we posit that metabolic rate is related to the fast–slow life history continuum and the connection may be stronger for maximum metabolic rate and aerobic scope compared to resting metabolic rate. Specifically, we ask whether variation in rmax or any of its component life‐history traits – age‐at‐maturity, maximum age, and annual reproductive output – explain variation in resting and maximum metabolic rates and aerobic scope across 84 shark and teleost species, while accounting for the effects of measurement temperature, measurement body mass, ecological lifestyle, and evolutionary history. Overall, we find a strong connection between metabolic rate and the fast‐slow life history continuum, such that species with faster population growth (higher rmax) generally have higher maximum metabolic rates and broader aerobic scopes. Specifically, rmax is more important in explaining variation in maximum metabolic rate and aerobic scope compared to resting metabolic rate, which is best explained by age‐at‐maturity (out of the life history traits examined). In conclusion, teleosts and sharks share a common fast–slow physiology/life history continuum, with teleosts generally at the faster end and sharks at the slower end, yet with considerable overlap. Our work improves our understanding of the diversity of fish life histories and may ultimately improve our understanding of intrinsic sensitivity to overfishing.

Invader at the edge - Genomic origins and physiological differences of round gobies across a steep urban salinity gradient.

Species invasions are a global problem of increasing concern, especially in highly connected aquatic environments. Despite this, salinity conditions can pose physiological barriers to their spread, and understanding them is important for management. In Scandinavia's largest cargo port, the invasive round goby (Neogobius melanostomus) is established across a steep salinity gradient. We used 12,937 SNPs to identify the genetic origin and diversity of three sites along the salinity gradient and round goby from western, central and northern Baltic Sea, as well as north European rivers. Fish from two sites from the extreme ends of the gradient were also acclimated to freshwater and seawater, and tested for respiratory and osmoregulatory physiology. Fish from the high-salinity environment in the outer port showed higher genetic diversity, and closer relatedness to the other regions, compared to fish from lower salinity upstream the river. Fish from the high-salinity site also had higher maximum metabolic rate, fewer blood cells and lower blood Ca2+. Despite these genotypic and phenotypic differences, salinity acclimation affected fish from both sites in the same way: seawater increased the blood osmolality and Na+ levels, and freshwater increased the levels of the stress hormone cortisol. Our results show genotypic and phenotypic differences over short spatial scales across this steep salinity gradient. These patterns of the physiologically robust round goby are likely driven by multiple introductions into the high-salinity site, and a process of sorting, likely based on behaviour or selection, along the gradient. This euryhaline fish risks spreading from this area, and seascape genomics and phenotypic characterization can inform management strategies even within an area as small as a coastal harbour inlet.

High Blood Flow Into the Femur Indicates Elevated Aerobic Capacity in Synapsids Since the Synapsida-Sauropsida Split

Varanids are the only non-avian sauropsids that are known to approach the warm-blooded mammals in stamina. Furthermore, a much higher maximum metabolic rate (MMR) gives endotherms (including birds) higher stamina than crocodiles, turtles, and non-varanid lepidosaurs. This has led researchers to hypothesize that mammalian endothermy evolved as a second step after the acquisition of elevated MMR in non-mammalian therapsids from a plesiomorphic state of low metabolic rates. In recent amniotes, MMR correlates with the index of blood flow into the femur (Qi), which is calculated from femoral length and the cross-sectional area of the nutrient foramen. Thus,Qimay serve as an indicator of MMR range in extinct animals. Using theQiproxy and phylogenetic eigenvector maps, here we show that elevated MMRs evolved near the base of Synapsida. Non-mammalian synapsids, including caseids, edaphosaurids, sphenacodontids, dicynodonts, gorgonopsids, and non-mammalian cynodonts, showQivalues in the range of recent endotherms and varanids, suggesting that raised MMRs either evolved in synapsids shortly after the Synapsida-Sauropsida split in the Mississippian or that the low MMR of lepidosaurs and turtles is apomorphic, as has been postulated for crocodiles.

The effect of metabolic phenotype on sociability and social group size preference in a coral reef fish

AbstractAlthough individuals within social groups experience reduced predation risk and find food patches more consistently, there can be competition for food among groupmates. Individuals with a higher standard metabolic rate (SMR) may be less social, to prioritize food acquisition over defense, while a greater maximum metabolic rate (MMR) may modulate sociability through increased competitive ability. Therefore, in theory, individuals with a higher SMR may prefer smaller groups and those with greater MMR may prefer larger groups. We examined links among metabolic phenotype, sociability, and choice of group size in the redbelly yellowtail fusilierCaesio cuning. Individuals were exposed to three association tests: (a) a choice between two fish or zero fish; (b) a choice between five fish or zero fish; and (c) a choice between two fish and five fish. The first two tests quantified sociability while the third measured relative group size choice. Although there was no link between SMR and sociability, fish with a higher MMR were more social than those individuals with a lower MMR. While no correlation was found between MMR and group size choice, there was weak evidence that, if anything, individuals with a higher SMR preferred larger groups, contrary to our hypothesis. AsC.cuningis an active fish that spends a large proportion of time operating above SMR, this result could suggest that the links between sociability and SMR may shift depending on a species’ routine behavior. Links between sociability and MMR may arise if competitive ability allows individuals to obtain resources within groups. Although metabolic traits had no significant influence on group size choice, variation in food availability or predation risk could alter the effects of metabolism on group size choice.

Metabolic traits in brown trout (Salmo trutta) vary in response to food restriction and intrinsic factors.

Metabolic rates vary hugely within and between populations, yet we know relatively little about factors causing intraspecific variation. Since metabolic rate determines the energetic cost of life, uncovering these sources of variation is important to understand and forecast responses to environmental change. Moreover, few studies have examined factors causing intraspecific variation in metabolic flexibility. We explore how extrinsic environmental conditions and intrinsic factors contribute to variation in metabolic traits in brown trout, an iconic and polymorphic species that is threatened across much of its native range. We measured metabolic traits in offspring from two wild populations that naturally show life-history variation in migratory tactics (one anadromous, i.e. sea-migratory, one non-anadromous) that we reared under either optimal food or experimental conditions of long-term food restriction (lasting between 7 and 17months). Both populations showed decreased standard metabolic rates (SMR-baseline energy requirements) under low food conditions. The anadromous population had higher maximum metabolic rate (MMR) than the non-anadromous population, and marginally higher SMR. The MMR difference was greater than SMR and consequently aerobic scope (AS) was higher in the anadromous population. MMR and AS were both higher in males than females. The anadromous population also had higher AS under low food compared to optimal food conditions, consistent with population-specific effects of food restriction on AS. Our results suggest different components of metabolic rate can vary in their response to environmental conditions, and according to intrinsic (population-background/sex) effects. Populations might further differ in their flexibility of metabolic traits, potentially due to intrinsic factors related to life history (e.g. migratory tactics). More comparisons of populations/individuals with divergent life histories will help to reveal this. Overall, our study suggests that incorporating an understanding of metabolic trait variation and flexibility and linking this to life history and demography will improve our ability to conserve populations experiencing global change.

Effects of repeated daily acute heat challenge on the growth and metabolism of a cold water stenothermal fish.

Temperature is an important environmental factor influencing fish physiology that varies both spatially and temporally in ecosystems. In small north temperate zone lakes, cold water piscivores rely on nearshore prey; however, this region exceeds the optimal temperature of the foraging species during summer. To cope, piscivores make short excursions into the nearshore to feed and return to cold water to digest their meal, but the physiological impacts of these repeated acute exposures to warm water are not well understood. We exposed juvenile lake trout (Salvelinus namaycush) to treatments where they were held at ∼10°C and exposed to either 17 or 22°C for 5-10 min daily for 53 days mimicking warm-water forays. Control fish, held at an average temperature of ∼10°C but not exposed to thermal variation, consumed more food and grew slightly faster than heat challenged fish, with no clear differences in body condition, hepatosomatic index, ventricle mass, or muscle concentrations of lactate dehydrogenase and cytochrome c oxidase. Aerobic metabolic rates measured at 10°C indicated that standard metabolic rates (SMR) were similar among treatments; however, fish that were repeatedly exposed to 17°C had higher maximum metabolic rates (MMR) and aerobic scopes (AS) than control fish and those repeatedly exposed to 22°C. There were no differences in MMR or AS between fish exposed to 22°C and control fish. These results suggest that although SMR of fish are robust to repeated forays into warmer environments, MMR displays plasticity, allowing fish to be less constrained aerobically in cold water after briefly occupying warmer waters.

Age-related changes of physiological performance and survivorship of bank voles selected for high aerobic capacity

Variation in lifespans is an intriguing phenomenon, but how metabolic rate influence this variation remains unclear. High aerobic capacity can result in health benefits, but also in increased oxidative damage and accelerated ageing. We tested these contradictory predictions using bank voles (Myodes=Clethrionomys glareolus) from lines selected for high swim-induced aerobic metabolism (A), which had about 50% higher maximum metabolic rate and a higher basal and routine metabolic rates, than those from unselected control lines (C). We measured sprint speed (VSmax), forced-running maximum metabolic rate (VO2run), maximum long-distance running speed (VLmax), running speed at VO2run (VVO2), and respiratory quotient at VO2run (RQ) at three age classes (I: 3–5, II: 12–14, III: 17–19months), and analysed survivorship. We asked if ageing, understood as the age-related decline of the performance traits, differs between the A and C lines. At age class I, voles from A lines had 19% higher VO2run, and 12% higher VLmax, but tended to have 19% lower VSmax, than those from C lines. RQ was nearly 1.0 for both A and C lines. The pattern of age-related changes differed between the lines mainly between age classes I and II, but not in older animals. VSmax increased by 27% in A lines and by 10% in C lines between age class I and II, but between classes II and III, it increased by 16% in both selection directions. VO2run decreased by 7% between age class I and II in A lines only, but in C lines it remained constant across all age classes. VLmax decreased by 8% and VVO2 by 12% between age classes II and III, but similarly in both selection directions. Mortality was higher in A than in C lines only between the age of 1 and 4months. The only trait for which the changes in old animals differed between the lines was RQ. In A lines, RQ increased between age classes II and III, whereas in C lines such an increase occurred between age classes I and II. Thus, we did not find obvious effects of selection on the pattern of ageing. However, the physiological performance and mortality of bank voles remained surprisingly robust to ageing, at least until the age of 17–19months, similar to the maximum lifespan under natural conditions. Therefore, it is possible that the selection could affect the pattern of ageing in even older individuals when symptoms of senility might be more profound.

Interpopulation variability of endocrine and metabolic response to cold stress in northern red-backed vole (Myodes rutilus)

In natural environment, stresses, when animals happen to be exposed to them, influence the functional activity of adrenal cortex. It can be expected that in animals, living under unfavorable conditions, basal concentration of glucocorticoid hormones would be increased while adrenocortical response to acute stress would be weakened. Since the main function of stress-reaction is resources mobilization meant to compensate an environmental impact, its weakening should lead to reduction of reserve metabolic capacities. To test this hypothesis, we compared energy metabolism, body temperature, and corticosterone concentration in blood plasma measured in northern red-back voles (Myodes rutilus) before and after acute cooling in helium-oxygen mixture. Voles belonged to two populations that deffered in relative abundance. It is found out that voles from a population of low relative abundance inhabiting the recreational forest of Novosibirsk Scientific Center, despite their being more stress-prone and having weakened stress-reaction, have higher maximum metabolic rate than voles from the mountain taiga polulation with high relative abundance. The results obtained suggest that living under unfavorable conditions leads to physiological adaptations which enhance resistance to acute stress, yet increase the risk of chronic stresses that have negative effect on fitness.

Phenotypic differences between the sexes in the sexually plastic mangrove rivulus fish (Kryptolebias marmoratus).

To maximize reproductive success, many animal species have evolved functional sex change. Theory predicts that transitions between sexes should occur when the fitness payoff of the current sex is exceeded by the fitness payoff of the opposite sex. We examined phenotypic differences between the sexes in a sex-changing vertebrate, the mangrove rivulus fish (Kryptolebias marmoratus), to elucidate potential factors that might drive the 'decision' to switch sex. Rivulus populations consist of self-fertilizing hermaphrodites and males. Hermaphrodites transition into males under certain environmental conditions, affording us the opportunity to generate 40 hermaphrodite-male pairs where, within a pair, individuals possessed identical genotypes despite being different sexes. We quantified steroid hormone levels, behavior (aggression and risk taking), metabolism and morphology (organ masses). We found that hermaphrodites were more aggressive and risk averse, and had higher maximum metabolic rates and larger gonadosomatic indices. Males had higher steroid hormone levels and showed correlations among hormones that hermaphrodites lacked. Males also had greater total mass and somatic body mass and possessed considerable fat stores. Our findings suggest that there are major differences between the sexes in energy allocation, with hermaphrodites exhibiting elevated maximum metabolic rates, and showing evidence of favoring investments in reproductive tissues over somatic growth. Our study serves as the foundation for future research investigating how environmental challenges affect both physiology and reproductive investment and, ultimately, how these changes dictate the transition between sexes.

Localised intraspecific variation in the swimming phenotype of a coral reef fish across different wave exposures

Wave-driven water flow is a major force structuring marine communities. Species distributions are partly determined by the ability to cope with variation in water flow, such as differences in the assemblage of fish species found in a given water flow environment being linked to swimming ability (based on fin shape and mode of locomotion). It remains unclear, however, whether similar assembly rules apply within a species. Here we show phenotypic variation among sites in traits functionally linked to swimming ability in the damselfish Acanthochromis polyacanthus. These sites differ in wave energy and the observed patterns of phenotypic differences within A. polyacanthus closely mirrored those seen at the interspecific level. Fish from high-exposure sites had more tapered fins and higher maximum metabolic rates than conspecifics from sheltered sites. This translates to a 36% larger aerobic scope and 33% faster critical swimming speed for fish from exposed sites. Our results suggest that functional relationships among swimming phenotypes and water flow not only structure species assemblages, but can also shape patterns of phenotypic divergence within species. Close links between locomotor phenotype and local water flow conditions appear to be important for species distributions as well as phenotypic divergence across environmental gradients.

Comparative Physiology and Relative Swimming Performance of Three Redhorse (Moxostomaspp.) Species: Associations with Fishway Passage Success

Our understanding of biological criteria to inform fish passage design is limited, partially due to the lack of understanding of biological motivators, cues, and constraints, as well as a lack of biological performance evaluations of structures once they are built. The Vianney-Legendre vertical slot fishway on the Richelieu River, Quebec, Canada, passes large numbers of migrating redhorse (Moxostoma spp.) upriver to spawning grounds each year. We evaluated the physiological capacity and relative swimming ability of three redhorse species (Moxostoma anisurum, Moxostoma carinatum, Moxostoma macrolepidotum; silver, river, and shorthead redhorse, respectively) to determine how these biotic factors relate to variation in fishway passage success and duration. Shorthead redhorse had higher maximum metabolic rates and were faster swimmers than silver and river redhorse at their species-specific peak migration temperatures. Blood lactate and glucose concentrations recovered more quickly for river redhorse than for silver and shorthead redhorse, and river redhorse placed second in terms of metabolic recovery and swim speed. Interestingly, fish sampled from the top of the fishway had nearly identical lactate, glucose, and pH values compared to control fish. Using passive integrated transponders in 2010 and 2012, we observed that passage success and duration were highly variable among redhorse species and were not consistent among years, suggesting that other factors such as water temperature and river flows may modulate passage success. Clearly, additional research is needed to understand how organismal performance, environmental conditions, and other factors (including abundance of conspecifics and other comigrants) interact with fishway features to dictate which fish will be successful and to inform research of future fishways. Our research suggests that there may be an opportunity for a rapid assessment approach where fish chased to exhaustion to determine maximal values of physiological disturbance are compared to fish sampled from the top of the fishway, which could reveal which species (or sizes of fish) are approaching or exceeding their physiological capacity during passage.

Effects of feeding and hypoxia on cardiac performance and gastrointestinal blood flow during critical speed swimming in the sea bass Dicentrarchus labrax

Previous studies have shown that if European sea bass are exercised after feeding, they can achieve a significantly higher maximum metabolic rate (MMR) than when fasted. They can meet combined metabolic demands of digestion (specific dynamic action, SDA) and maximal aerobic exercise, with no decline in swimming performance. If, however, exposed to mild hypoxia (50% saturation), bass no longer achieve higher MMR after feeding but they swim as well fed as fasted, due to an apparent ability to defer the SDA response. This study explored patterns of cardiac output ( Q A) and blood flow to the gastrointestinal tract ( Q GI) associated with the higher MMR after feeding, and with the ability to prioritise swimming in hypoxia. Sea bass (mean mass ~ 325 g, forklength ~ 27 cm) were instrumented with flow probes to measure Q A and Q GI during an incremental critical swimming speed ( U crit) protocol in a tunnel respirometer, to compare each animal either fasted or 6 h after a meal of fish fillet equal to 3% body mass. Feeding raised oxygen uptake ( M O2) prior to exercise, an SDA response associated with increased Q A (+ 30%) and Q GI (+ 100%) compared to fasted values. As expected, when exercised the fed bass maintained the SDA load throughout the protocol and achieved 14% higher MMR than when fasted, and the same U crit (~ 100 cm s -1). Both fed and fasted bass showed pronounced increases in Q A and decreases in Q GI during exercise and the higher MMR of fed bass was not associated with higher maximum Q A relative to when fasted, or to any differences in Q GI at maximum Q A. In hypoxia prior to exercise, metabolic and cardiac responses to feeding were similar compared to normoxia. Hypoxia caused an almost 60% reduction to MMR and 30% reduction to U crit, but neither of these traits differed between fed or fasted bass. Despite hypoxic limitations to MMR and U crit, maximum Q A and patterns of Q GI during exercise in fasted and fed bass were similar to normoxia. Estimating GI oxygen supply from Q GI indicated that the ability of bass to prioritise aerobic exercise over SDA when metabolically limited by hypoxia was linked to an ability to defer elements of the SDA response occurring outside the GI tract.