Metabolic Rate Of Fish Research Articles

Is repeatability of metabolic rate influenced by social separation? A test with a teleost fish.

Metabolic rates are typically thought to have important influences on fitness and more broadly be relevant to the ecology and evolution of animals. Previous studies demonstrate that metabolic rates are repeatable to a certain extent under constant conditions, but how social conditions influence the repeatability of metabolic rate remains largely unknown. In this study, we investigated the repeatability of resting metabolic rate (RMR) in the highly social crucian carp (Carassius auratus) after being socially separated for different time periods relative to control fish that were not socially separated. We found that RMR was repeatable in fish in the control group, while the repeatability of RMR disappeared quickly (even within 7 days) when fish were exposed to social separation. This study is the first to our knowledge to examine the role of social separation for different time periods on the repeatability of intra-individual physiological variation in fish. We highlight that the inter-individual repeatability of metabolic rate can be substantial over time but was eliminated by social separation. The findings indicate that the repeatability of metabolic rate in fish is condition dependent, and that the change in repeatability of metabolic rate should not be overlooked when considering the ecological and evolutionary effects of environmental change.

Invasive lionfish have turbocharged digestive systems

Wreathed with delicate-looking fronds, lionfish (Pterois spp.) are a delight to behold in their natural habitat. ‘They appear to just lazily swim very slowly around a reef’, says Erika Eliason, from the University of California, Santa Barbara, USA. However, in the wrong place, they're an ecological catastrophe. Thanks to their voracious appetites, they have aggressively colonised the eastern Mediterranean Sea and western Atlantic Ocean, obliterating the small fish and crustacean populations upon which they dine, shattering local ecosystems. So when Clay Steell joined Steven Cooke's lab at Carleton University, Canada, to study the physiology of fish in The Bahamas, the ferocious predators seemed the ideal species to investigate. And Cooke quickly invited ecophysiologist Eliason to join the team as it was apparent that the fish's appetites lay at the heart of their success.‘That led us to wonder if they have a specialized digestive physiology that might enable them to eat large meals’, says Eliason, who joined Steell at the Cape Eleuthera Institute, The Bahamas, to start investigating the fish. ‘Clay was an excellent lionfish captor’, she chuckles, recalling how they trapped the fish between two nets while SCUBA diving to avoid coming into contact with the animal's venomous spines. Back at the institute, Steell, Eliason and Travis Van Leeuwen waited until the lionfish were hungry before allowing the animals to stuff themselves on tasty silversides. Then they measured the lionfish's oxygen consumption as they digested the meals – ranging from 0.6% to 13.8% of their body mass – at 26°C and 32°C (winter and summer temperatures in The Bahamas), before converting the animals’ oxygen consumption into the amount of energy they consumed during digestion. Fortunately, as Eliason recalls, the lionfish were remarkably relaxed in the respirometry chamber compared with the trout and salmon that she has worked with in the past. Steell then calculated the fish's metabolic rates after chasing the animals around a tank, to compare with the amount of energy they consumed when digesting a meal.Amazingly, the lionfish put far more effort into digesting dinner than they exerted dashing around, consuming 1.7 times as much energy when digesting a large meal at 32°C as they did scurrying about. ‘Lionfish have a physiology that prioritises feeding over movement’, says Steell. And when the team compared the lionfish's diets at 26°C and 32°C, it was clear that the animals were able to consume almost 50% more during the summer months and digest it 45% faster.Eliason suspects that the lionfish's venomous spines, which protect them from predators, may give them a head start over more benign local species because they do not need to hold energy in reserve to take evasive action when threatened; with those spines, nothing is going to take them on. And she is concerned that lionfish may become even more of a menace as temperatures rise and their turbocharged appetites become more voracious, allowing them to decimate local populations even more effectively as they grow ever faster.

Prediction of Mercury Elimination Rate Coefficients of Fish is Improved by Incorporating Fish Temperature Classification into Models.

This study evaluated the dependence of mercury (Hg) elimination by fish on species specific fish metabolic rate in order to generate improved algorithms of Hg elimination rate coefficients. Mercury elimination rate coefficient observations were collected by literature review and fish routine metabolic rate (RMR) estimates calculated using the Wisconsin Fish Bioenergetics Model. Three models were compared that considered body weight, temperature, thermal category, Hg depuration period and RMR as predictors of Hg elimination. The best performing model incorporated body size, temperature and fish thermal category, explaining 79% of the variation of the calibration data and between 20% and 69% of the variation of validation data sets. The results support the conclusion that species-specific differences in metabolic rate influence mercury elimination by fish but also highlight major data gaps in the mercury toxicokinetic literature necessary to develop robust models Hg elimination by fish.

Konsumsi Oksigen Ikan Uceng Nemacheilus fasciatus (Valenciennes, 1846) pada Kondisi Padat Tebar yang Berbeda

<strong>Oxygen Consumption of Barred Loach Nemacheilus fasciatus (Valenciennes, 1846) under Different Stocking Densities</strong>. In aquaculture system, fish growth is affected by stocking densities. One way to predict the effect of stocking density on growth is to determine fish metabolic rate through oxygen consumption measurements. In Barred loach Nemacheilus fasciatus (Valenciennes, 1846), the information was scarce on oxygen consumption. This study was to analyze the effect of stocking density on oxygen consumption in Barred loach conducted at Research Institute for Freshwater Aquaculture and Fisheries Extension, Bogor in May 2018. Barred loach (total length: 5.79 ± 0.47 cm, weight: 1.32 ± 0.34 g) was observed its oxygen consumption on three different stocking densities (5, 10, and 15 fish/L) by using closed respirometers (volume: 1.4 L) with three replications of each treatment. Measurement of oxygen consumption was carried out under normoxia and hypoxia conditions. In addition, fish behavior and ventilation rate were also observed and recorded according to treatment. The results showed that the highest oxygen consumption of barred loach was found in the stocking density of 5 fish/L (1250.6 ± 128.4 mg O2/kg/h) which was significantly different from the stocking density of 10 fish/L (626.9 ± 46.7 mg O2/kg/h) and 15 fish/L (596.9 ± 48.9 mg O2/kg/h). Meanwhile, oxygen consumption of barred loach under hypoxic conditions decreased significantly compared to normoxic conditions, which was marked by a decrease in their swimming activities. Although the ventilation rate in hypoxic conditions has decreased, the value was not significantly different from those of normoxia condition. Results of this study provide information that an increase in stocking density and hypoxic conditions in barred loach caused a decrease in oxygen consumption rates. In addition, this study showed that the critical oxygen level for barred loach was around 3.1 mg/L

Metabolic phenotype is not associated with vulnerability to angling in bluegill sunfish (Lepomismacrochirus)

Prior work has described a link between an individual’s metabolic rate and a willingness to take risks. One context in which high metabolic rates and risk-prone behaviors may prove to be maladaptive is in fish that strike fishing lures only to be captured by anglers. It has been shown that metabolic phenotype may be altered by angling; however, little work has assessed metabolic rate in fish and its relationship to angling vulnerability in a realistic angling trial. To address this, we subjected a set of bluegill sunfish (Lepomis macrochirus Rafinesque, 1819) to a series of angling sessions. Following this, a subset of 23 fish that had been captured at least once and 25 fish that had not been captured were assessed for metabolic phenotype (standard and maximum metabolic rates, postexercise oxygen consumption, and recovery time) via intermittent flow respirometry. Contrary to predictions, captured and uncaptured fish did not differ in any measurement of metabolic rate. These results suggest that metabolic phenotype is not a determinant of angling vulnerability within the studied context. It is possible, therefore, that previously described alterations in metabolic phenotype owing to angling pressure may be context-specific and may not apply to all species and angling contexts.

Metabolic Costs of Feeding Predictively Alter the Spatial Distribution of Individuals in Fish Schools

Group living is ubiquitous among animals [1, 2], but the exact benefits of group living experienced by individual groupmates is related to their spatial location within the overall group [3-5]. Individual variation in behavioral traits and nutritional state is known to affect interactions between individuals and their social group [6, 7], but physiological mechanisms underpinning collective animal behavior remain largely unexplored [8]. Here, we show that while fish at the front of moving groups are most successful at capturing food items, these individuals then show a systematic, post-feeding movement toward the rear of groups. Using observations of fish feeding in groups coupled with estimates of metabolic rate in fish consuming different meal sizes, we demonstrate that the magnitude of this shift in spatial position is directly related to the aerobic metabolic scope remaining after accounting for energetic costs of digestion. While previous work has shown that hungry individuals occupy anterior positions in moving groups [9, 10], our results show that the metabolic demand of food processing reduces the aerobic capacity available for locomotion in individuals that eat most, thus preventing them from maintaining leading positions. This basic trade-off between feeding and locomotor capacity could fundamentally dictate the spatial position of individuals within groups, perhaps obviating the role of individual traits in determining spatial preferences over shorter timescales (e.g., hours to days). This may be a general constraint for individuals within animal collectives, representing a key, yet overlooked, mediator of group functioning that could affect leadership, social information transfer, and group decision making.

Comment on 'Measurement and relevance of maximum metabolic rate in fishes by Norin & Clark (2016)'.

Comment on 'Measurement and relevance of maximum metabolic rate in fishes by Norin & Clark (2016)'.

Physiological Challenges to Fishes in a Warmer and Acidified Future.

With the projected levels of global warming and ocean acidification, fishes have to face warmer waters with CO2 levels that are the highest in over 30 million years. The resultant rise in body temperature means that metabolic rates of fish will increase, and some may become energetically compromised. No less worrying, and maybe more surprising, is that rising CO2 concentrations appear to trigger pH regulatory mechanisms that disrupts neural ion gradients, leading to altered neurotransmitter function and maladaptive behavioral changes. We point out the many outstanding questions, including the ultimate one: Will fish be able to adapt to these challenges?

Do method and species lifestyle affect measures of maximum metabolic rate in fishes?

The rate at which active animals can expend energy is limited by their maximum aerobic metabolic rate (MMR). Two methods are commonly used to estimate MMR as oxygen uptake in fishes, namely during prolonged swimming or immediately following brief exhaustive exercise, but it is unclear whether they return different estimates of MMR or whether their effectiveness for estimating MMR varies among species with different lifestyles. A broad comparative analysis of MMR data from 121 fish species revealed little evidence of different results between the two methods, either for fishes in general or for species of benthic, benthopelagic or pelagic lifestyles.

Temperature and its impact on predation risk within aquatic ecosystems

Metabolic rates of fish and their activity levels have thermal optima. When environmental temperatures are below these optima, increasing temperature will increase their rates of energy consumption, resulting in a corresponding increase in the risk of starvation. For that reason we predicted that within this temperature range, food is of greater value at higher temperatures so fish should be willing to incur greater costs to obtain it. To test this hypothesis, we measured how the activity and foraging rates of the fathead minnow (Pimephales promelas) changed with temperature at 4, 15, and 24 °C. As expected, fish activity and foraging were greater at higher temperatures. We then measured the impact of predation risk on foraging decisions at 5, 15, and 23 °C. At 5 and 15 °C, the risk of predation had a significant effect on foraging decisions, but there was no effect at 23 °C. These results demonstrate that increasing temperatures below their optimal level diminish the impact of predation risk on foraging behaviour and may mean that the direct consumptive effect of predators on aquatic communities will be greater at warmer temperatures while the risk of predation will become a less important factor, and vice versa.

The determination of standard metabolic rate in fishes.

This review and data analysis outline how fish biologists should most reliably estimate the minimal amount of oxygen needed by a fish to support its aerobic metabolic rate (termed standard metabolic rate; SMR). By reviewing key literature, it explains the theory, terminology and challenges underlying SMR measurements in fishes, which are almost always made using respirometry (which measures oxygen uptake, ṀO2 ). Then, the practical difficulties of measuring SMR when activity of the fish is not quantitatively evaluated are comprehensively explored using 85 examples of ṀO2 data from different fishes and one crustacean, an analysis that goes well beyond any previous attempt. The main objective was to compare eight methods to estimate SMR. The methods were: average of the lowest 10 values (low10) and average of the 10% lowest ṀO2 values, after removing the five lowest ones as outliers (low10%), mean of the lowest normal distribution (MLND) and quantiles that assign from 10 to 30% of the data below SMR (q0·1 , q0·15 , q0·2 , q0·25 and q0·3 ). The eight methods yielded significantly different SMR estimates, as expected. While the differences were small when the variability was low amongst the ṀO2 values, they were important (>20%) for several cases. The degree of agreement between the methods was related to the c.v. of the observations that were classified into the lowest normal distribution, the c.v. MLND (C.V.MLND ). When this indicator was low (≤5·4), it was advantageous to use the MLND, otherwise, one of the q0·2 or q0·25 should be used. The second objective was to assess if the data recorded during the initial recovery period in the respirometer should be included or excluded, and the recommendation is to exclude them. The final objective was to determine the minimal duration of experiments aiming to estimate SMR. The results show that 12 h is insufficient but 24 h is adequate. A list of basic recommendations for practitioners who use respirometry to measure SMR in fishes is provided.

Metabolic rate in fishes: definitions, methods and significance for conservation physiology

Metabolic rate in fishes: definitions, methods and significance for conservation physiology

EFFECTS OF SALINITY ON OXYGEN CONSUMPTION AND BLOOD PROPERTIES OF YOUNG GREY MULLETS Mugil cephalus

Oxygen consumption (OC) is one of important factors in aquaculture activities, as the oxygen is a vital condition for all the organisms living in the water and having an aerobic type of respiration. OC is the preferred method for measuring and reporting the metabolic rate in fish. The aims of this study were to evaluate the effects of salinity on OC and blood properties of grey mullets. Five experimental groups were conducted to measure OC and blood properties of grey mullets Mugil cephalus (BW: 187.9 ± 45.8 g) according to salinity (30→0 psu, 0→30 psu) changes; SDS: fish reared in seawater (SW, 30 psu) directly shifted to SW, SGF: SW fish gradually shifted to freshwater (FW, 0 psu), SDF: SW fish directly shifted to FW, FDF: FW fish directly shifted to FW, and FDS: FW fish directly shifted to SW. The result showed that OC tended to decrease in the groups of SW fish shifted to FW showing 194.5 mg O2/kg/h at 25°C in SDS to 82.4 mg O2/kg/h at 15°C in SGF. On the contrary, OC increased in the groups of FW fish shifted to SW showing 80.5 mg O2/kg/h at 15°C in FDF to 184.0 mg O2/kg/h at 25°C in FDS. Cortisol levels at the end of experiments were rapidly increased with the lowering salinities in SW fish shifted to FW showing 20.6 ng/mL in SDS to 316.2 ng/mL in SDF, while those were decreased with the increasing salinities in FW fish shifted to SW showing 40.2 ng/mL in FDF to 10.3 ng/mL in FDS. However, glucose levels showed no significant differences among all experimental groups. Based on the information from this study, aquaculture of grey mullet might be applied or developed in freshwater due to its osmotic adaptation ability.

Alcoholic pupfish kick breathing oxygen

Deep in a warm pool in a limestone cavern in the Mojave Desert lives one of the rarest species on earth: the Devils Hole pupfish (Cyprinodon diabolis). With a current population of just 131 adults, the race is on to secure the fish's future. ‘One possible cause for the small population size of C. diabolis is limited food availability’, says Frank van Breukelen from the University of Nevada Las Vegas, USA. Realising that the dark conditions dramatically limit the amount of food that grows in the cavern to support the fish, van Breukelen and his colleague, Stanley Hillyard, were curious to know how many pupfish the restricted ecosystem could sustain. However, before they could do the calculation, the duo needed to measure the scarce fish's metabolic rate. As the native Devils Hole pupfish population is too endangered to study directly, van Breukelen and Hillyard measured the metabolic rate of a refuge population of the fish that had been established as an insurance policy should the population ever be wiped out. But when they performed the measurement, the duo stumbled across an unexpected paradox.Recording the fish's oxygen consumption at temperatures ranging from 25 to 38°C, Matt Heuton found that they consumed oxygen at a stable rate of around 300 μl h−1 when they came from a population that had been raised at 28°C. However, when Heuton measured the oxygen consumption rate of fish raised at 33°C – the temperature in the Devils Hole spring – something went wrong. The fish appeared to stop consuming oxygen. ‘My initial reaction was that there was a malfunction of the electrode’, laughs van Breukelen. However, after testing 295 animals, van Breukelen and Hillyard had to concede that the phenomenon was real. The fish were somehow switching from aerobic metabolism to anaerobic metabolism, which was perplexing as anaerobic metabolism is nowhere near as effective as aerobic metabolism – only yielding 1/15 the amount of ATP per glucose molecule generated by aerobic metabolism. Why were the fish indulging in such a profligate practice?Intrigued, the team tested whether the phenomenon was the result of the refuge C. diabolis population breeding with another closely related species, Cyprinodon nevadensis mionectes. van Breukelen explains that it has been suggested that interbreeding with other pupfish could have compromised the function of the mitochondria that generate ATP. However, when the team measured the oxygen consumption patterns of the two species, they both performed paradoxical anaerobism, so there was no mitochondrial disruption. And when the team tested whether C. diabolis were switching to paradoxical anaerobism because they had depressed metabolism, they found that the fish were still wafting their gill covers to take in oxygen, so they weren't depressing their metabolism. Finally, the team checked whether C. diabolis were switching to paradoxical anaerobism because there simply was not enough oxygen to sustain aerobic metabolism in the warm conditions. However, even that theory did not hold water.‘We were going nuts trying to figure out what triggers paradoxical anaerobism’, admits van Breukelen, until he and Heuton embarked on an animated brain-storming session one night. It occurred to them that the fish may be switching to paradoxical anaerobism to avoid the toxic side-effects of aerobic metabolism, producing ethanol instead. They knew that the 33°C-acclimated fish naturally produced high levels of ethanol – 7.3 times more than the fish from cooler water: could the ethanol be switching off aerobic energy production and stalling oxygen consumption? ‘I said, “Let's get the fish drunk”’, recalls van Breukelen. And when the team added ethanol to the fish's water, even the fish that were adapted to cooler water switched to paradoxical anaerobism. So Devils Hole pupfish switch off aerobic metabolism to avoid the toxic side-effect of an aerobic lifestyle, despite the expense.

Measurement and relevance of maximum metabolic rate in fishes

Maximum (aerobic) metabolic rate (MMR) is defined here as the maximum rate of oxygen consumption (M˙O2max ) 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.

Measuring oxygen uptake in fishes with bimodal respiration.

Respirometry is a robust method for measurement of oxygen uptake as a proxy for metabolic rate in fishes, and how species with bimodal respiration might meet their demands from water v. air has interested researchers for over a century. The challenges of measuring oxygen uptake from both water and air, preferably simultaneously, have been addressed in a variety of ways, which are briefly reviewed. These methods are not well-suited for the long-term measurements necessary to be certain of obtaining undisturbed patterns of respiratory partitioning, for example, to estimate traits such as standard metabolic rate. Such measurements require automated intermittent-closed respirometry that, for bimodal fishes, has only recently been developed. This paper describes two approaches in enough detail to be replicated by the interested researcher. These methods are for static respirometry. Measuring oxygen uptake by bimodal fishes during exercise poses specific challenges, which are described to aid the reader in designing experiments. The respiratory physiology and behaviour of air-breathing fishes is very complex and can easily be influenced by experimental conditions, and some general considerations are listed to facilitate the design of experiments. Air breathing is believed to have evolved in response to aquatic hypoxia and, probably, associated hypercapnia. The review ends by considering what realistic hypercapnia is, how hypercapnic tropical waters can become and how this might influence bimodal animals' gas exchange.

How does a fish's metabolic rate influence its performance in a changing environment?

Event Abstract Back to Event How does a fish's metabolic rate influence its performance in a changing environment? Neil Metcalfe1* 1 University of Glasgow, United Kingdom Fish provide some of the best-studied examples of marked intraspecific variation in metabolic rate: after accounting for variation in size and age, there can typically be a 2-3 fold variation among individual fish for both standard and maximum metabolic rate (SMR and MMR), and also in their aerobic scope (AS, the difference between SMR and MMR and hence a fish’s capacity to increase its aerobic metabolism). These differences are relatively stable over time, although individual fish differ in the extent to which they can alter their metabolism when environmental conditions change. In this presentation I will briefly consider the extent and causes of individual variation in SMR, MMR and AS, considering both the mechanistic basis (e.g. individual variation in mitochondrial performance) and its origins, including a consideration of genetic and maternal effects. I will then describe both documented and potential links between metabolism, behaviour and performance. Intraspecific variation in metabolism has been found to be related to other traits. As an example, fish with a relatively high SMR tend to be more dominant, digest food faster and grow faster than those with a low SMR, but these advantages only apply in environments where the food supply is high and predictable; in less favourable environments they lose their advantage, and are more prone to risk-taking when conditions deteriorate. Less is known about the ecological consequences of individual variation in MMR and AS, although fish with a higher AS are known to have advantages in some contexts. This is especially important in the context of climate change, since it has been suggested that constraints on AS may underlie the poor performance of fishes at higher temperatures. Given these links between metabolism and measures of performance, understanding the metabolic responses of individuals to changing environments will be a key area for future research. Keywords: Fishes, metabolic rate, performance, environment, Climate Change Conference: XV European Congress of Ichthyology, Porto, Portugal, 7 Sep - 11 Sep, 2015. Presentation Type: Plenary Invited Presentation Topic: Physiology, Behavior and Toxicology Citation: Metcalfe N (2015). How does a fish's metabolic rate influence its performance in a changing environment?. Front. Mar. Sci. Conference Abstract: XV European Congress of Ichthyology. doi: 10.3389/conf.FMARS.2015.03.00230 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 16 Dec 2015; Published Online: 16 Dec 2015. * Correspondence: PhD. Neil Metcalfe, University of Glasgow, Glasgow, United Kingdom, neil.metcalfe@glasgow.ac.uk Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Neil Metcalfe Google Neil Metcalfe Google Scholar Neil Metcalfe PubMed Neil Metcalfe Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Swimming fish stick to same Strouhal number

Fish swimming at a certain speed appear to adopt a narrow range of swimming styles instinctively. Robert Nudds and colleagues from the University of Manchester, UK, explain that fish seem to adapt their undulations so that the product of their tail beat frequency and the maximum displacement of the tail tip when divided by the fish's forward velocity almost always converges to a number ranging from 0.2 to 0.4, known as the Strouhal number. This means that, at a certain swimming speed, if the fish beats its tail faster it compensates by dropping the amplitude of the tail's undulation, or if the tail beats become broader, they slow down. The same phenomenon, where movements are conserved to a narrow range of Strouhal numbers during locomotion, has also been found in bird flight, leading scientists to conclude that animal movements have been tightly constrained by evolution to maximise propulsive efficiency. However, Nudds points out that none of the observations that have directed scientists to this conclusion had been collected systematically, so Nudds, Emma John, Adam Keen and Holly Shiels decided to resolve the problem by investigating how trout adjust their swimming styles in warmer waters (p. 2244).The team explains that ectothermic fish are susceptible to the environmental temperature, so when the temperature rises, the fish's metabolic rate rises also, reducing the amount of energy that they can invest in swimming at higher speeds and affecting how they beat their tails. With that in mind, the scientists filmed young trout swimming at speeds from 0.28 to 1.11 m s−1 in water at temperatures of 11 and 20°C while recording the fish's tail beat frequency and amplitude.After painstakingly analysing hours of swimming data to calculate the fish's Strouhal number at different speeds and temperatures, the team could see that the fish maintained the same Strouhal number when swimming at both the low and high temperatures at any given speed. The hotter fish beat their tails faster than the cooler fish, but they compensated by reducing the amplitude of each tail beat to maintain a constant Strouhal number at that speed. ‘This is the first experimental evidence for an apparent adherence to a preferred (perhaps optimum) Strouhal number for an animal using oscillatory propulsion’, the team says.However, when they calculated how the fish's Strouhal number varied as the animals speeded up, they saw that the number gradually increased from 0.19 at the lowest speeds to 0.22 at the highest. Although the fish continued beating their tails at the same rate, they increased their speed by sweeping the tail further. The team suggests that the fish's apparent inability to increase their tail beat frequency indicates that their muscle contraction frequency might be finely tuned to a very narrow range at any given temperature. And when they measured the metabolic rate of the fish, although the animals' basal metabolic rate increased with temperature, they did not have to increase the amount of effort they put into fast swimming at higher temperatures. The team suggests that small increases in water temperature may even benefit trout swimming performance. They conclude by saying, ‘Future predictions of changes to water temperature of lakes and rivers are only 5–10°C over the next 100 years and it appears that rainbow trout, at least, can cope with this easily in terms of swimming biomechanics.’

Effectiveness of eugenol sedation to reduce the metabolic rates of cool and warm water fish at high loading densities

Effects of eugenol (AQUI-S®20E, 10% active eugenol) sedation on cool water, yellow perch Perca flavescens (Mitchill), and warm water, Nile tilapia Oreochromis niloticus L. fish metabolic rates were assessed. Both species were exposed to 0, 10, 20 and 30 mg L−1 eugenol using static respirometry. In 17°C water and loading densities of 60, 120 and 240 g L−1, yellow perch controls (0 mg L−1 eugenol) had metabolic rates of 329.6–400.0 mg O2 kg−1 h−1, while yellow perch exposed to 20 and 30 mg L−1 eugenol had significantly reduced metabolic rates of 258.4–325.6 and 189.1–271.0 mg O2 kg−1 h−1 respectively. Nile tilapia exposed to 30 mg L−1 eugenol had a significantly reduced metabolic rate (424.5 ± 42.3 mg O2 kg−1 h−1) relative to the 0 mg L−1 eugenol control (546.6 ± 53.5 mg O2 kg−1 h−1) at a loading density of 120 g L−1 in 22°C water. No significant differences in metabolic rates for Nile tilapia were found at 240 or 360 g L−1 loading densities when exposed to eugenol. Results suggest that eugenol sedation may benefit yellow perch welfare at high densities (e.g. live transport) due to a reduction in metabolic rates, while further research is needed to assess the benefits of eugenol sedation on Nile tilapia at high loading densities.

Estimating activity-specific energy expenditure in a teleost fish, using accelerometer loggers

The ability to define and quantify the behaviour and energetic costs of different activities is fundamental to a full understanding of fish ecology and movement, but monitoring activity and measuring energy expenditure in fish in the field is problematic. New telemetry methods using data loggers that incorporate tri-axial accelerometers promise to provide a method for simultaneously recording the behaviour and activity-specific energy use in both the laboratory and field. Using electronic data loggers equipped with tri-axial accelerometers we have measured dynamic body acceleration (DBA) during aerobic exercise in European sea bass Dicentrarchus labrax whilst swimming in a swim-tunnel respirometer at ambient water temperatures of between 5.5 and 17.5°C. For all individuals, dynamic body acceleration (both vectorial dynamic body accel- eration (VeDBA) and overall dynamic body acceleration (ODBA)) scaled linearly with oxygen con- sumption and as a function of ambient temperature. When the 2 DBA metrics were compared, VeDBA was not significantly different from ODBA, though the value for Akaike's information cri- terion was lower for VeDBA (indicating a better fit for the VeDBA model). In this paper, we pro- vide further evidence to support the use of acceleration as a means to quantify the activity-specific energetic costs of swimming in teleosts and highlight some of the problems associated with monitoring the activity and metabolic rate of fish in restricted laboratory conditions.