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Highly variable thermal environments, such as coral reef flats, are challenging for marine ectotherms and are thought to invoke the use of behavioural strategies to avoid extreme temperatures and seek out thermal environments close to their preferred temperatures. Common to coral reef flats, the epaulette shark (Hemiscyllium ocellatum) possesses physiological adaptations to hypoxic and hypercapnic conditions, such as those experienced on reef flats, but little is known regarding the thermal strategies used by these sharks. We investigated whether H. ocellatum uses behavioural thermoregulation (i.e., movement to occupy thermally favourable microhabitats) or tolerates the broad range of temperatures experienced on the reef flat. Using an automated shuttlebox system, we determined the preferred temperature of H. ocellatum under controlled laboratory conditions and then compared this preferred temperature to 6 months of in situ environmental and body temperatures of individual H. ocellatum across the Heron Island reef flat. The preferred temperature of H. ocellatum under controlled conditions was 20.7 +/- 1.5 degrees C, but the body temperatures of individual H. ocellatum on the Heron Island reef flat mirrored environmental temperatures regardless of season or month. Despite substantial temporal variation in temperature on the Heron Island reef flat (15-34 degrees C during 2017), there was a lack of spatial variation in temperature across the reef flat between sites or microhabitats. This limited spatial variation in temperature creates a low-quality thermal habitat limiting the ability of H. ocellatum to behaviourally thermoregulate. Behavioural thermoregulation is assumed in many shark species, but it appears that H. ocellatum may utilize other physiological strategies to cope with extreme temperature fluctuations on coral reef flats. While H. ocellatum appears to be able to tolerate acute exposure to temperatures well outside of their preferred temperature, it is unclear how this, and other, species will cope as temperatures continue to rise and approach their critical thermal limits. Understanding how species will respond to continued warming and the strategies they may use will be key to predicting future populations and assemblages.

The present study determined the effect of body mass and acclimation temperature (15-28°C) on oxygen consumption rate (ṀO2 ) and the size dependency of preferred temperature in European perch Perca fluviatilis. Standard metabolic rate (SMR) scaled allometrically with body mass by an exponent of 0.86, and temperature influenced SMR with a Q10 of 1.9 regardless of size. Maximum metabolic rate (MMR) and aerobic scope (MMR-SMR) scaled allometrically with body mass by exponents of 0.75-0.88. The mass scaling exponents of MMR and aerobic scope changed with temperature and were lowest at the highest temperature. Consequently, the optimal temperature for aerobic scope decreased with increasing body mass. Notably, fish

Many vertebrate animals employ anaerobic pathways during high-speed exercise, even if it imposes an energetic cost during postexercise recovery, expressed as excess postexercise oxygen consumption (EPOC). In ectotherms such a fish, the initial anaerobic contribution to exercise is often substantial. Even so, fish may recover from anaerobic pathways as swimming exercise ensues and aerobic metabolism stabilizes, thus total energetic costs of exercise could depend on swimming duration and subsequent physiological recovery. To test this hypothesis, we examined EPOC in striped surfperch (Embiotoca lateralis) that swam at high speeds (3.25 L s-1 ) during randomly ordered 2-, 5-, 10-, and 20-min exercise periods. We found that EPOC was highest after the 2-min period (20.9 mg O2 kg-1 ) and lowest after the 20-min period (13.6 mg O2 kg-1 ), indicating that recovery from anaerobic pathways improved with exercise duration. Remarkably, EPOC for the 2-min period accounted for 72% of the total O2 consumption, whereas EPOC for the 20-min period only accounted for 14%. Thus, the data revealed a striking decline in the total cost of transport from 0.772 to 0.226 mg O2 ·kg-1 ·m-1 during 2- and 20-min periods, respectively. Our study is the first to combine anaerobic and aerobic swimming costs to demonstrate an effect of swimming duration on EPOC in fish. Clarifying the dynamic nature of exercise-related costs is relevant to extrapolating laboratory findings to animals in the wild.

Fast escape responses to a predator threat are fundamental to the survival of mobile marine organisms. However, elasmobranchs are often underrepresented in such studies. Here, we measured the escape latency (time interval between the stimulus and first visible reaction) of mechanically induced escape responses in the Pacific spiny dogfish

This study investigated the oxygen consumption of the putative oxygen conformer marbled swamp eel Synbranchus marmoratus during progressive hypoxia. Earlier studies have not reached agreement on whether S. marmoratus is a conformer or regulator. Our results support the view that S. marmoratus is an oxygen regulator, like most bony fishes.

© 2020. Published by The Company of Biologists Ltd. Billfishes are well known for their distinctive elongated rostra, i.e. bills. The functional significance of billfish rostra has been frequently discussed and the recent discovery of an oil gland (glandula oleofera) at the base of the rostrum in swordfish, Xiphias gladius, has added an interesting facet to this discussion regarding the potential co-evolution of gland and rostra. Here, we investigated the oil gland and oil pores (through which the oil is brought to the skin surface) of four billfish species - swordfish, Atlantic blue marlin (Makaira nigricans), Indo-Pacific sailfish (Istiophorus platypterus) and striped marlin (Kajikia audax) - and provide detailed evidence for the presence of an oil gland in the last three. All four species had a high density of oil pores on the forehead which is consistent with the hypothesis of hydrodynamic benefits of the oil. The extension of the pores onto the front half of the rostrum in sailfish and striped marlin, but not in swordfish or blue marlin, suggests that the oil may have additional functions. One such function could be linked to the antibacterial and anti-inflammatory properties of the oil. However, the available evidence on predatory rostrum use (and hence the likelihood of tissue damage) is only partly consistent with the extension of pores on rostra across species. We conclude that the oil gland probably serves multiple, non-mutually exclusive functions. More detailed information on rostrum use in blue marlin and swordfish is needed to better link behavioural and morphological data with the aim of accomplishing a full comparative analysis.

Temperature has a profound effect on all life and a particularly influential effect on ectotherms, such as fishes. Amphibious fishes have a variety of strategies, both physiological and/or behavioural, to cope with a broad range of thermal conditions. This study examined the relationship between prolonged (5 weeks) exposure to a range of temperatures (22, 25, 28, or 32 degrees C) on oxygen uptake rate and movement behaviours (i.e., thermoregulation and emergence) in a common amphibious fish, the barred mudskipper (Periophthalmus argentilneatuis). At the highest temperature examined (32 degrees C, approximately 5 degrees C above their summer average temperatures), barred mudskippers exhibited 33.7-97.7% greater oxygen uptake rates at rest ((M) over dotO(2Rest)), emerged at a higher temperature (CTe; i.e., a modified critical thermal maxima (CTMax) methodology) of 41.3 +/- 0.3 degrees C relative to those maintained at 28, 25, or 22 degrees C. The 32 degrees C-maintained fish also ceased movement activity at the highest holding temperature suggesting that prolonged submergence at elevated temperatures is physiologically and energetically stressful to the individual. Using exhaustive exercise protocols with and without air exposure to simulate a predatory chase, the time to recovery was examined for all individuals. When submerged, mudskippers required 2.5x longer recovery time to return to resting oxygen uptake from exhaustive exercise than those fully emerged in air. Oxygen uptake data revealed that air exposure did not accrue oxygen debt, thereby allowing faster return to resting oxygen consumption rates. If the option to emerge was not available, mudskippers preferentially sought more benign water temperatures (26.7 +/- 2.1 degrees C), resembling those experienced by these fish during the Austral autumn, regardless of prolonged exposure higher or lower temperatures. These results add to our understanding of the strategies that amphibious fishes may use to mitigate extra costs associated with living in warm waters, and could be the key to understanding how such species will cope with increasing temperatures in the future.

Increasing ocean temperatures and the resulting poleward range shifts of species has highlighted the importance of a species preferred temperature and thermal range in shaping ecological communities. Understanding the temperatures preferred and avoided by individual species, and how these are influenced by species interactions is critical in predicting the future trajectories of populations, assemblages, and ecosystems. Using an automated shuttlebox system, we established the preferred temperature and upper and lower threshold temperatures (i.e., avoided temperatures) of a common coral reef fish, the black-axil chromis, Chromis atripectoralis. We then investigated how the presence of conspecifics, heterospecifics (Neopomacentrus bankieri), or a predator (Cephalopholis spiloparaea) influenced the selection of these temperatures. Control C. atripectoralis preferred 27.5 ± 1.0 °C, with individuals avoiding temperatures below 23.5 ± 0.9 °C and above 29.7 ± 0.7 °C. When associating with either conspecifics or heterospecifics, C. atripectoralis selected significantly lower temperatures (conspecifics: preferred = 21.2 ± 1.4 °C, lower threshold = 18.1 ± 0.8 °C; heterospecifics: preferred = 21.1 ± 1.1 °C, lower threshold = 19.2 ± 0.9 °C), but not higher temperatures (conspecifics: preferred = 28.9 ± 1.2 °C, upper threshold = 30.8 ± 0.9 °C; heterospecifics: preferred = 29.7 ± 1.1 °C, upper threshold = 31.4 ± 0.8 °C). The presence of the predator, however, had a significant effect on both lower and upper thresholds. Individual C. atripectoralis exposed themselves to temperatures ~ 5.5 °C cooler or warmer (lower threshold: 18.6 ± 0.5 °C, upper threshold: 35.2 ± 0.5 °C) than control fish before moving into the chamber containing the predator. These findings demonstrate how behavioural responses due to species interactions influence the thermal ecology of a tropical reef fish; however, there appears to be limited scope for individuals to tolerate higher temperatures unless faced with the risk of predation.

Unsteady, dynamic flow regimes commonly found in shallow marine ecosystems such as coral reefs pose an energetic challenge for mobile organisms that typically depend on station holding for fitness-related activities. The majority of experimental studies, however, have measured energetic costs of locomotion at steady speeds, with only a few studies measuring the effects of oscillatory flows. In this study, we used a bidirectional swimming respirometer to create six oscillatory water flow regimes consisting of three frequency and amplitude combinations for both unidirectional and bidirectional oscillatory flows. Using the goldring surgeonfish, Ctenochaetus strigosus, a pectoral-fin (labriform) swimmer, we quantified the net cost of swimming (swimming metabolic rate minus standard metabolic rate) associated with station-holding under these various conditions. We determined that the swimming costs of station-holding in the bidirectional flow regime increased by 2-fold compared with costs based on swimming over the same range velocities at steady speeds. Furthermore, as we found minimal differences in energetic costs associated with station-holding in the unidirectional, oscillating-flow compared with that predicted from steady swimming costs, we conclude that the added acceleration costs are minimal, while the act of turning is an energetically expensive endeavor for this reef fish species.

Linking morphological differences in foraging adaptations to prey choice and feeding strategies has provided major evolutionary insights across taxa. Here, we combine behavioural and morphological approaches to explore and compare the role of the rostrum (bill) and micro-teeth in the feeding behaviour of sailfish ( Istiophorus platypterus ) and striped marlin ( Kajikia audax ) when attacking schooling sardine prey. Behavioural results from high-speed videos showed that sailfish and striped marlin both regularly made rostrum contact with prey but displayed distinct strategies. Marlin used high-speed dashes, breaking schools apart, often contacting prey incidentally or tapping at isolated prey with their rostra; while sailfish used their rostra more frequently and tended to use a slower, less disruptive approach with more horizontal rostral slashes on cohesive prey schools. Capture success per attack was similar between species, but striped marlin had higher capture rates per minute. The rostra of both species are covered with micro-teeth, and micro-CT imaging showed that species did not differ in average micro-tooth length, but sailfish had a higher density of micro-teeth on the dorsal and ventral sides of their rostra and a higher amount of micro-teeth regrowth, suggesting a greater amount of rostrum use is associated with more investment in micro-teeth. Our analysis shows that the rostra of billfish are used in distinct ways and we discuss our results in the broader context of relationships between morphological and behavioural feeding adaptations across species.

The Greenland shark (Somniosus microcephalus, Squaliformes: Somniosidae) is a long-lived Arctic top predator, which in combination with the high historical and modern fishing pressures, has made it subject to increased scientific focus in recent years. Key aspects of reproduction are not well known as exemplified by sparse and contradictory information e.g. on birth size and number of pups per pregnancy. This study represents the first comprehensive work on Greenland shark reproductive biology based on data from 312 specimens collected over the past 60 years. We provide guidelines quantifying reproductive parameters to assess specific maturation stages, as well as calculate body length-at-maturity (TL50) which was 2.84±0.06 m for males and 4.19±0.04 m for females. From the available information on the ovarian fecundity of Greenland sharks as well as a meta-analysis of Squaliform reproductive parameters, we estimate up to 200–324 pups per pregnancy (depending on maternal size) with a body length-at-birth of 35–45 cm. These estimates remain to be verified by future observations from gravid Greenland sharks.

We conducted in vitro inflations of freshly excised ventral aortas of the Greenland shark, Somniosus microcephalus , and used pressure–diameter data to estimate the point of transition from high to low compliance, which has been shown to occur at the mean blood pressure in other vertebrates including fishes. We also determined the pressure at which the modulus of elasticity of the aorta reached 0.4 MPa, as occurs at the compliance transition in other species. From these analyses, we predict the average ventral aortic blood pressure in S. microcephalus to be about 2.3–2.8 kPa, much lower than reported for other sharks. Our results support the idea that this species is slow moving and has a relatively low aerobic metabolism. Histological investigation of the ventral aorta shows that elastic fibres are present in relatively low abundance and loosely connected, consistent with this aorta having high compliance at a relatively low blood pressure.

Background/Aims: Microvascular blood flow is essential for healing and predicts surgical outcome. The aim of the current study was to investigate the relation between fluxes measured with the laser speckle contrast imaging (LSCI) technique and changes in absolute blood flow. In addition, we studied the reproducibility of the LSCI technique when assessing the intra-abdominal microcirculation of the pig. Methods: During trial 1, a fish gill arch was mechanically perfused with heparinized fish blood under controlled stepwise-altered flow rates alongside mechanically induced movement artefacts. The microcirculation of the fish gill was simultaneously assessed with the LSCI technique. In trial 2, microcirculation was measured in the stomach, liver, and small intestine of 10 pigs by two observers. Results: A linear correlation was observed between flux and volumetric flow. During conditions of no volumetric flow, the high recording speed with the LSCI technique registered the movement artefacts as flow signals. The LSCI measurements showed good correlation and agreement between the two observers when assessing microcirculation in the stomach, liver, and small intestine (r2 = 0.857, 0.956, and 0.946; coefficients of variation = 6.0, 3.2, and 6.4%, respectively). Conclusion: Due to the non-contact and real-time assessment over large areas, LSCI is a promising technique for the intraoperative assessment of intra-abdominal microcirculation. A linear correlation between flux and volumetric flow was found, in accordance with previous experimental studies. However, movement artefacts affect flux measurements, and the choice of the sampling speed must be made with care, depending on the given setting.

Billfishes are considered among the fastest swimmers in the oceans. Despite early estimates of extremely high speeds, more recent work showed that these predators (e.g., blue marlin) spend most of their time swimming slowly, rarely exceeding 2 m s(-1). Predator-prey interactions provide a context within which one may expect maximal speeds both by predators and prey. Beyond speed, however, an important component determining the outcome of predator-prey encounters is unsteady swimming (i.e., turning and accelerating). Although large predators are faster than their small prey, the latter show higher performance in unsteady swimming. To contrast the evading behaviors of their highly maneuverable prey, sailfish and other large aquatic predators possess morphological adaptations, such as elongated bills, which can be moved more rapidly than the whole body itself, facilitating capture of the prey. Therefore, it is an open question whether such supposedly very fast swimmers do use high-speed bursts when feeding on evasive prey, in addition to using their bill for slashing prey. Here, we measured the swimming behavior of sailfish by using high-frequency accelerometry and high-speed video observations during predator-prey interactions. These measurements allowed analyses of tail beat frequencies to estimate swimming speeds. Our results suggest that sailfish burst at speeds of about 7 m s(-1) and do not exceed swimming speeds of 10 m s(-1) during predator-prey interactions. These speeds are much lower than previous estimates. In addition, the oscillations of the bill during swimming with, and without, extension of the dorsal fin (i.e., the sail) were measured. We suggest that extension of the dorsal fin may allow sailfish to improve the control of the bill and minimize its yaw, hence preventing disturbance of the prey. Therefore, sailfish, like other large predators, may rely mainly on accuracy of movement and the use of the extensions of their bodies, rather than resorting to top speeds when hunting evasive prey.

Changes in ambient temperature affect the physiology and metabolism and thus the distribution of fish. In this study we used intermittent flow respirometry to determine the effect of temperature (2, 5, 10, 15 and 20°C) and wet body mass (BM) (~30-460g) on standard metabolic rate (SMR, mgO2h(-1)), maximum metabolic rate (MMR, mgO2h(-1)) and metabolic scope (MS, mgO2h(-1)) of juvenile Atlantic cod. SMR increased with BM irrespectively of temperature, resulting in an average scaling exponent of 0.87 (0.82-0.92). Q10 values were 1.8-2.1 at temperatures between 5 and 15°C but higher (2.6-4.3) between 2 and 5°C and lower (1.6-1.4) between 15 and 20°C in 200 and 450g cod. MMR increased with temperature in the smallest cod (50g) but in the larger cod MMR plateaued between 10, 15 and 20°C. This resulted in a negative correlation between the optimal temperature for MS (Topt) and BM, Topt being respectively 14.5, 11.8 and 10.9°C in a 50, 200 and 450g cod. Irrespective of BM cold water temperatures resulted in a reduction (30-35%) of MS whereas the reduction of MS at warm temperatures was only evident for larger fish (200 and 450g), caused by plateauing of MMR at 10°C and above. Warm temperatures thus seem favourable for smaller (50g) juvenile cod, but not for larger conspecifics (200 and 450g).

Fish swimming energetics are often measured in laboratory environments which attempt to minimize turbulence, though turbulent flows are common in the natural environment. To test whether the swimming energetics and kinematics of shiner perch

Carassius carassius responds to hypoxic conditions by conversion of lactate into ethanol, which is excreted over the gills. However, a closely related species, Cyprinus carpio, does not possess the ability to produce ethanol and would be expected to accumulate lactate during hypoxic exposure. While the increase in oxygen consumption in fish required following strenuous exercise or low environmental oxygen availability has been frequently considered, the primary contributing mechanism remains unknown. This study utilized the close relationship but strongly divergent physiology between C. carpio and C. carassius to examine the possible correlation between excess post-hypoxic oxygen consumption (EPHOC) and lactate accumulation. No difference in the EPHOC:O2 deficit ratio was observed between the two species after 2.5 h anoxia, with ratios of 2.0 ± 0.6 (C. carpio) and 1.3 ± 0.3 (C. carassius). As predicted, lactate accumulation dynamics did significantly differ between the species in both plasma and white muscle following anoxic exposure. Significant lactate accumulation was seen in both plasma and muscle in C. carpio, but there was no accumulation of lactate in white muscle tissue of C. carassius. These findings indicate that lactate accumulated as a consequence of 2.5 h anoxic exposure is not a major determinant of the resulting EPHOC

Lateralization is widespread throughout the animal kingdom [1; 2; 3; 4; 5; 6 ; 7] and can increase task efficiency via shortening reaction times and saving on neural tissue [8; 9; 10; 11; 12; 13; 14; 15 ; 16]. However, lateralization might be costly because it increases predictability [17; 18; 19; 20 ; 21]. In predator-prey interactions, for example, predators might increase capture success because of specialization in a lateralized attack, but at the cost of increased predictability to their prey, constraining the evolution of lateralization. One unexplored mechanism for evading such costs is group hunting: this would allow individual-level specialization, while still allowing for group-level unpredictability. We investigated this mechanism in group hunting sailfish, Istiophorus platypterus, attacking schooling sardines, Sardinella aurita. During these attacks, sailfish alternate in attacking the prey using their elongated bills to slash or tap the prey [ 22; 23 ; 24]. This rapid bill movement is either leftward or rightward. Using behavioral observations of identifiable individual sailfish hunting in groups, we provide evidence for individual-level attack lateralization in sailfish. More strongly lateralized individuals had a higher capture success. Further evidence of lateralization comes from morphological analyses of sailfish bills that show strong evidence of one-sided micro-teeth abrasions. Finally, we show that attacks by single sailfish are indeed highly predictable, but predictability rapidly declines with increasing group size because of a lack of population-level lateralization. Our results present a novel benefit of group hunting: by alternating attacks, individual-level attack lateralization can evolve, without the negative consequences of individual-level predictability. More generally, our results suggest that group hunting in predators might provide more suitable conditions for the evolution of strategy diversity compared to solitary life.

The costs and benefits of group living often depend on the spatial position of individuals within groups and the ability of individuals to occupy preferred positions. For example, models of predation events for moving prey groups predict higher mortality risk for individuals at the periphery and front of groups. We investigated these predictions in sardine (Sardinella aurita) schools under attack from group hunting sailfish (Istiophorus platypterus) in the open ocean. Sailfish approached sardine schools about equally often from the front and rear, but prior to attack there was a chasing period in which sardines attempted to swim away from the predator. Consequently, all sailfish attacks were directed at the rear and peripheral positions of the school, resulting in higher predation risk for individuals at these positions. During attacks, sailfish slash at sardines with their bill causing prey injury including scale removal and tissue damage. Sardines injured in previous attacks were more often found in the rear half of the school than in the front half. Moreover, injured fish had lower tail-beat frequencies and lagged behind uninjured fish. Injuries inflicted by sailfish bills may, therefore, hinder prey swimming speed and drive spatial sorting in prey schools through passive self-assortment. We found only partial support for the theoretical predictions from current predator–prey models, highlighting the importance of incorporating more realistic predator–prey dynamics into these models.This article is part of the themed issue ‘Physiological determinants of social behaviour in animals’.

We present evidence of a novel form of group hunting. Individual sailfish (Istiophorus platypterus) alternate attacks with other group members on their schooling prey (Sardinella aurita). While only 24% of attacks result in prey capture, multiple prey are injured in 95% of attacks, resulting in an increase of injured fish in the school with the number of attacks. How quickly prey are captured is positively correlated with the level of injury of the school, suggesting that hunters can benefit from other conspecifics' attacks on the prey. To explore this, we built a mathematical model capturing the dynamics of the hunt. We show that group hunting provides major efficiency gains (prey caught per unit time) for individuals in groups of up to 70 members. We also demonstrate that a free riding strategy, where some individuals wait until the prey are sufficiently injured before attacking, is only beneficial if the cost of attacking is high, and only then when waiting times are short. Our findings provide evidence that cooperative benefits can be realized through the facilitative effects of individuals' hunting actions without spatial coordination of attacks. Such ‘proto-cooperation’ may be the pre-cursor to more complex group-hunting strategies.

The free radical theory of ageing predicts that long-lived species should be more resistant to oxidative damage than short-lived species. Although many studies support this theory, recent studies found notable exceptions that challenge the generality of this theory. In this study, we have analysed the oxidative status of the Greenland shark (Somniosus microcephalus), which has recently been found as the longest living vertebrate animal known to science with a lifespan of at least 272 years. As compared to other species, the Greenland shark had body mass corrected values of muscle glutathione peroxidase and red blood cells protein carbonyls (metric of protein oxidative damage) above 75 percentile and below 25 percentile, respectively. None of the biochemical metrics of oxidative status measured in either skeletal muscle or red blood cells were correlated with maximum lifespan of species. We propose that the values of metrics of oxidative status we measured might be linked to ecological features (e.g., adaptation to cold waters and deep dives) of this shark species rather to its lifespan. (C) 2016 Elsevier Inc. All rights reserved.

Deep living for centuries We tend to think of vertebrates as living about as long as we do, give or take 50 to 100 years. Marine species are likely to be very long-lived, but determining their age is particularly difficult. Nielsen et al. used the pulse of carbon-14 produced by nuclear tests in the 1950s—specifically, its incorporation into the eye during development—to determine the age of Greenland sharks. This species is large yet slow-growing. The oldest of the animals that they sampled had lived for nearly 400 years, and they conclude that the species reaches maturity at about 150 years of age. Science , this issue p. 702

Previous studies hailed thermal tolerance and the capacity for organisms to acclimate and adapt as the primary pathways for species survival under climate change. Here we challenge this theory. Over the past decade more than 365 tropical stenothermal fish species have been documented moving pole-ward, away from ocean warming hotspots where temperatures 2-3 °C above long-term annual means can compromise critical physiological processes. We examined the capacity of a model species - a thermally-sensitive coral reef fish, Chromis viridis (Pomacentridae) – to use preference behaviour to regulate its body temperature. Movement could potentially circumvent the physiological stress response associated with elevated temperatures and may be a strategy relied upon before genetic adaptation can be effectuated. Individuals were maintained at one of six temperatures (23, 25, 27, 29, 31 and 33 °C) for at least six weeks. We compared the relative importance of acclimation temperature to changes in upper critical thermal limits, aerobic metabolic scope, and thermal preference. While acclimation temperature positively affected the upper critical thermal limit, neither aerobic metabolic scope nor thermal preference exhibited such plasticity. Importantly, when given the choice to stay in a habitat reflecting their acclimation temperatures or relocate, fish acclimated to end-of-century predicted temperatures (i.e., 31 or 33 °C) preferentially sought out cooler temperatures, those equivalent to long-term summer averages in their natural habitats (~29 °C). This was also the temperature providing the greatest aerobic metabolic scope and body condition across all treatments. Consequently, acclimation can confer plasticity in some performance traits, but may be an unreliable indicator of the ultimate survival and distribution of mobile stenothermal species under global warming. Conversely, thermal preference can arise long before, and remain long after, the harmful effects of elevated ocean temperatures take hold and may be the primary driver of the escalating pole-ward migration of species.

The present study was undertaken to examine cardiac responses to some of the temperature challenges that eels encounter in their natural environment. The contractile properties of ventricular muscle was studied on electrically paced tissue strips after long term acclimation at 0 °C, 10 °C, or 20 °C, and following acute ± 10 °C temperature changes. The time-course of contraction, and thus maximal attainable heart rates, was greatly influenced by working temperature, but was independent of acclimation history. The absolute force of contraction and power production (i.e. the product of force and stimulation frequency) was significantly influenced by acute temperature decrease from 20 °C to 10 °C. The role of adrenaline as a modulator of contraction force, power production, rates of contraction and relaxation, and minimum time in contraction was assessed. Increased adrenergic tonus elicited a positive inotropic, temperature-dependent response, but did not influence twitch duration. This suggests that adrenaline acts as an agent in maintaining an adequate contractile force following temperature challenges. A significant increased relative ventricular mass was observed in 0 °C and 10 °C-acclimated eels compared to 20 °C-acclimated, which suggests that at low temperatures, eels secure cardiac output by heart enlargement. Inhibition of specific sarcolemmal Ca(2+) channels by selective drug treatment revealed that, depending on temperature, L-type channels is the major entry site, but also that reverse-mode Na(+)/Ca(2+)-exchange and store operated calcium entry contribute to the pool of activator Ca(2+).

At the end of May, 17 scientists involved in an EU COST Action on Conservation Physiology of Marine Fishes met in Oristano, Sardinia, to discuss how physiology can be better used in modelling tools to aid in management of marine ecosystems. Current modelling approaches incorporate physiology to different extents, ranging from no explicit consideration to detailed physiological mechanisms, and across scales from a single fish to global fishery resources. Biologists from different sub-disciplines are collaborating to rise to the challenge of projecting future changes in distribution and productivity, assessing risks for local populations, or predicting and mitigating the spread of invasive species.

The schooling behaviour of fish is of great biological importance, playing a crucial role in the foraging and predator avoidance of numerous species. The extent to which physiological performance traits affect the spatial positioning of individual fish within schools is completely unknown. Schools of juvenile mulletLiza auratawere filmed at three swim speeds in a swim tunnel, with one focal fish from each school then also measured for standard metabolic rate (SMR), maximal metabolic rate (MMR), aerobic scope (AS) and maximum aerobic swim speed. At faster speeds, fish with lower MMR and AS swam near the rear of schools. These trailing fish required fewer tail beats to swim at the same speed as individuals at the front of schools, indicating that posterior positions provide hydrodynamic benefits that reduce swimming costs. Conversely, fish with high aerobic capacity can withstand increased drag at the leading edge of schools, where they could maximize food intake while possibly retaining sufficient AS for other physiological functions. SMR was never related to position, suggesting that high maintenance costs do not necessarily motivate individuals to occupy frontal positions. In the wild, shifting of individuals to optimal spatial positions during changing conditions could influence structure or movement of entire schools.

The blood and lymphatic vasculatures are structurally and functionally coupled in controlling tissue perfusion, extracellular interstitial fluids, and immune surveillance. Little is known, however, about the molecular mechanisms that underlie the regulation of bloodlymphatic vessel connections and lymphatic perfusion. Here we show in the adult zebrafish and glass catfish ( Kryptopterus bicirrhis ) that blood-lymphatic conduits directly connect arterial vessels to the lymphatic system. Under hypoxic conditions, arterial-lymphatic conduits (ALCs) became highly dilated and linearized by NO-induced vascular relaxation, which led to blood perfusion into the lymphatic system. NO blockage almost completely abrogated hypoxia-induced ALC relaxation and lymphatic perfusion. These findings uncover mechanisms underlying hypoxia-induced oxygen compensation by perfusion of existing lymphatics in fish. Our results might also imply that the hypoxia-induced NO pathway contributes to development of progression of pathologies, including promotion of lymphatic metastasis by modulating arterial-lymphatic conduits, in the mammalian system.

The functional significance of chemoreflexive hypoxic bradycardia was explored in Atlantic cod Gadus morhua L. (mean mass ∼ 800 g, acclimated to a seawater temperature of 11 °C) by investigating responses to progressive hypoxia following section of the cardiac branches of cranial nerve X. Cardiac denervation had no effect on oxygen uptake rate ( M O 2 ), gill ventilation rate ( f G ) or opercular pressure amplitude ( P OP ) under normoxic conditions, but caused a significant increase in heart rate ( f H ), to 50 ± 1 beats min − 1 by comparison to 40 ± 2 beats min − 1 in sham-operated cod (mean ± s.e.m., n = 9). Sham-operated cod exhibited transient profound bradycardia following oxygen chemoreceptor stimulation by bolus injection of sodium cyanide into the buccal cavity (2 mg in 2 ml seawater), but this cardiac chemoreflex was abolished in denervated cod. Both groups, however, exhibited similar marked transient chemoreflexive hyperventilation following NaCN. When exposed from normoxia ( P O 2 ∼ 18 kPa) to progressive hypoxia at nominal water P O 2 's of 8, 6, 5, 4 and 3 kPa, both groups exhibited the same pattern of homeostatic regulation of M O 2 , with no significant difference in their mean critical P O 2 ( P crit ) values, which were 7.40 ± 0.81 kPa and 8.73 ± 0.71 kPa, respectively ( n = 9). Both groups exhibited significant bradycardia during progressive hypoxia, although denervated fish always had higher mean f H . The incipient threshold for bradycardia coincided with P crit in sham-operated cod whereas, in denervates, the threshold was below their P crit and bradycardia presumably reflected direct effects of hypoxia on the myocardium. The sham-operated group displayed a significantly more pronounced ventilatory response than denervates in hypoxia, in particular for P OP . In sham-operated cod, peak ventilatory responses occurred in deep hypoxia below P crit whereas, in denervates, more modest peak responses coincided with P crit and, in deep hypoxia, they exhibited a significant decline in f G below their normoxic rate. Only a minority of shams lost equilibrium in hypoxia whereas a majority of denervates did, some of which failed to recover. The results indicate that chemoreflexive bradycardia plays no role in the homeostatic regulation of oxygen uptake by cod in hypoxia, but does contribute to maintenance of overall functional integrity below P crit .

We assessed the functional properties in atrial and ventricular myocardium (using isolated cardiac strips) of smooth dogfish (Mustelus canis), clearnose skate (Raja eglanteria), and sandbar shark (Carcharhinus plumbeus) by blocking Ca2+ release from the sarcoplasmic reticulum (SR) with ryanodine and thapsigargin and measuring the resultant changes in contraction–relaxation parameters and the force–frequency relationship at 20 °C and 30 °C. We also examined ultrastructural differences with electron microscopy. In tissues from smooth dogfish, net force (per cross-sectional area) and measures of the speeds of contraction and relaxation were all higher in atrial than ventricular myocardium at both temperatures. Atrial-ventricular differences were evident in the other two species primarily in measures of the rates of contraction and relaxation. Ryanodine-thapsigargin treatment reduced net force and its maximum positive first derivative (i.e., contractility), and increased time to 50 % relaxation in atrial tissue from smooth dogfish at 30 °C. It also increased times to peak force and half relaxation in clearnose skate atrial and ventricular tissue at both temperatures, but only in atrial tissue from sandbar shark at 30 °C; indicating that SR involvement in excitation–contraction (EC) coupling is species- and temperature-specific in elasmobranch fishes, as it is in teleost fishes. Atrial and ventricular myocardium from all three species displayed a negative force–frequency relationship, but there was no evidence that SR involvement in EC coupling was influenced by heart rate. SR was evident in electron micrographs, generally located in proximity to mitochondria and intercalated discs, and to a lesser extent between the myofibrils; with mitochondria being more numerous in ventricular than atrial myocardium in all three species.

Fluorescein isothiocyanate dextran (FITC-dextran) exchange between the primary (PCS) and secondary (SCS) circulatory systems in the Atlantic cod, Gadus morhua (Linnaeus, 1752), were studied using 20-kDa (n = 4) and 500-kDa (n = 4) FITC-dextran. In order to give a qualitative perspective of the general connection between the PCS and SCS, distribution of plasma-borne tracers (FITC-dextran) in the PCS and SCS were examined. In this study, a total of eight cod were cannulated in the ventral aorta (PCS) and dorsal cutaneous vessel (SCS), for investigation of FITC-dextran disappearance in the PCS and its subsequent appearance in the SCS. FITC-dextran of both sizes was found to be in equilibrium between the PCS and SCS in less than 20 min. This indicates a profound connection between the PCS and SCS in the Atlantic cod, and rapid mixing of tracers between the PCS and SCS. The destination of the injected 500-kDa FITC-dextran was also examined, and it was observed that of the 500-kDa FITC-dextran lost from the primary and secondary vascular systems, 63.0 +/- 9.2% could be recovered from the liver.

We present the first data on the effect of hypoxia on the specific dynamic action (SDA) in a teleost fish. Juvenile cod (Gadus morhua) were fed meals of 2.5% and 5% of their wet body mass (BM) in normoxia (19.8 kPa Po2) and 5% BM in hypoxia (6.3 kPa Po2). Reduced O2 availability depressed the postprandial peaks of oxygen consumption, and to compensate for this, the total SDA duration lasted \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $212.0\pm 20$ \end{document} h in hypoxia, compared with \documentclass{aastex} \use...

The relationship between whole blood-oxygen affinity (P(50)) and pH-dependent binding (i.e., cooperativity and the Bohr [ Phi ] and Root effects) was examined statistically under standardized conditions (10.0 degrees Celsius) in four unrelated cold-temperate marine fishes that differ widely in their swimming performance and their expected responses to hypoxia: cod (Gadus morhua), herring (Clupea harengus), mackerel (Scomber scombrus), and plaice (Pleuronectes platessa). An unexpected difference in blood-oxygen affinity was found (herringplaicemackerelcod), and this was independent of both swimming performance and the predicted low O(2) response of each species. The ecotype of the four marine species was also unrelated to pH-dependent binding because no difference in the Bohr effect was apparent ( Phi varied insignificantly from -0.90 to -1.06), and differences in the magnitude of the cooperative binding reaction were associated only with the presence of the Root effect. Although several reviews propose a generalized link between blood-oxygen affinity and pH-dependent binding, our results advise against overestimating the adaptive functional properties of hemoglobin across unrelated species.

European eels were exposed for 6 weeks to water CO(2) partial pressures (P(CO)(2)) from ambient (approx. 0.8 mmHg), through 15+/-1 mmHg and 30+/-1 mmHg to 45+/-1 mmHg in water with a total hardness of 240 mg l(-1) as CaCO(3), pH 8.2, at 23+/-1 degrees C. Arterial plasma P(CO)(2) equilibrated at approximately 2 mmHg above water P(CO)(2) in all groups, and plasma bicarbonate accumulated up to 72 mmol l(-1) in the group at a water P(CO)(2) of 45 mmHg. This was associated with an equimolar loss of plasma Cl(-), which declined to 71 mmol l(-1) at the highest water P(CO)(2). Despite this, extracellular acid-base compensation was incomplete; all hypercapnic groups tolerated chronic extracellular acidoses and reductions in arterial blood O(2) content (Ca(O)(2)), of progressive severity with increasing P(CO)(2). All hypercapnic eels, however, regulated the intracellular pH of heart and white muscle to the same levels as normocapnic animals. Hypercapnia had no effect on such indicators of stress as plasma catecholamine or cortisol levels, plasma osmolality or standard metabolic rate. Furthermore, although Ca(O)(2) was reduced by approximately 50% at the highest P(CO)(2), there was no effect of hypercapnia on the eels' tolerance of hypoxia, aerobic metabolic scope or sustained swimming performance. The results indicate that, at the levels tested, chronic hypercapnia was not a physiological stress for the eel, which can tolerate extracellular acidosis and extremely low Cl(-) levels while compensating tissue intracellular pH, and which can meet the O(2) requirements of routine and active metabolism despite profound hypoxaemia.

SUMMARYThe volume of the primary (PCS) and secondary (SCS) circulatory system in the Atlantic cod Gadus morhua was determined using a modified dye dilution technique. Cod (N=10) were chronically cannulated in the second afferent branchial artery with PE-50 tubing. Evans Blue dye was bound to harvested fish plasma at a concentration of 1 mg dye ml-1plasma, and injected at a concentration of 1 mg kg-1 body mass. Serial sampling from the cannula produced a dye dilution curve, which could be described by a double exponential decay equation. Curve analysis enabled the calculation of the primary circulatory and total distribution volume. The difference between these volumes is assumed to be the volume of the SCS. From the dilution curve, it was also possible to calculate flow rates between and within the systems. The results of these experiments suggest a plasma volume in the PCS of 3.42±0.89 ml 100 g-1 body mass, and in the SCS of 1.68±0.35 ml 100 g-1 body mass (mean ± S.D.) or approximately 50% that of the PCS. Flow rates to the SCS were calculated as 2.7% of the resting cardiac output. There was an allometric relationship between body mass and blood volumes. Increasing condition factor showed a tendency towards smaller blood volumes of the PCS, expressed as percentage body mass, but this was not evident for the volume of the SCS.

SUMMARYAtlantic cod Gadus morhua has polymorphic haemoglobin, which can be separated into two homozygous types, HbI-1 and HbI-2, and one heterozygous type HbI-1/2. The geographical distribution of Atlantic cod with the different haemoglobin types varies, with the HbI2 allele occurring at high frequency in northern regions, and the HbI1 allele dominant in warmer areas. To determine if temperature is a selective parameter in the distribution of the haemoglobin types, the preferred temperature of the homozygous genotypes HbI-1 and HbI-2 was measured. We found that HbI-2 cod preferred a temperature of 8.2±1.5°C while HbI-1 cod preferred 15.4±1.1°C, and this preference was significant. The effect of hypoxia (35% oxygen saturation) on the preferred temperature was also measured. Previous studies showed that the preferred temperature of fish decreases during hypoxia, and this was the case for HbI-1 cod, which preferred 9.8±1.8°C during hypoxia, whereas HbI-2 cod did not show this effect. The results indicate that environmental temperature changes will lead to a distributional change in the different haemoglobin types of Atlantic cod,global warming providing an advantage for HbI-1 cod. However, since HbI-1 cod prefer a low temperature under hypoxic conditions, a combination of increased water temperature and hypoxia could be unfavourable for Atlantic cod stocks.

Land-based aquaculture systems expose fish to elevated dissolved CO2 levels, a factor that is correlated with reduced growth, feed conversion efficiency and body condition index. The physiological basis underlying the pathological effects of environmental hypercapnia is poorly understood, in particular for marine fish species. We investigated whether changes in energy expenditure and the specific dynamic action (SDA) of digestion and assimilation could account for the lower growth of adult Atlantic cod (Gadus morhua) under environmental hypercapnia. Fish acclimated to a partial pressure of 800 μatm CO2 (0.6 mmHg, 1.5 mg/L) and 9200 μatm CO2 (7 mmHg, 18.7 mg/L) exhibited no difference in maintenance metabolic rates, which concurs with previous research for this species and other fish species. At 9200 μatm CO2 Atlantic cod had a significantly diminished (14%) maximum aerobic capacity. While hypercapnia did not affect the amount of oxygen required for the SDA process, it did prolong the SDA duration by 23%. The longer SDA process time may offer an explanation for the observation of lower feed intake, growth and condition factor in long-term hypercapnia studies. Comparison of aerobic scope and cardiac performance during digestion suggested that reduced oxygen delivery capacity under hypercapnia could be one mechanism by which CO2 prolongs SDA, although our results could not definitively demonstrate this effect.

Growth requires that energy is directed towards ingestion, digestion, absorption and assimilation of a meal; energy expenditures are often expressed as the specific dynamic action (SDA). While SDA is an important part of fish energy budgets and strongly affected by water temperature, temperature effects are not known across a wide temperature range in Atlantic cod Gadus morhua. The objective of this study was to examine effects of temperature (2, 5, 10, 15 or 20 °C) on the energetic cost and time used for SDA in juvenile G. morhua by intermittent flow respirometry. At each temperature, G. morhua were fed a meal of herring (Clupea harengus) corresponding to 5 % of the body mass. Standard metabolic rates measured pre-feeding and post-feeding metabolic rates were measured to determine SDA. The study showed that SDA coefficients (%, SDA energy divided by meal energy) were significantly lower at 2 and 10 °C (5.4–6.3 %) compared to 5, 15 and 20 °C (10.4–12.4 %), while SDA duration increased significantly from 80 h at 10 °C to 130–160 h at 2, 15 and 20 °C and reached a maximum of 250 h at 5 °C. The significant decrease in SDA duration at 10 °C combined with a low SDA coefficient suggests that water temperatures close to 10 °C may represent the optimum temperatures for SDA in this population of G. morhua. Our results suggest that SDA is not a simple function of temperature, but may vary with temperature in a more complex fashion.

The istiophorid family of billfishes is characterized by an extended rostrum or ‘bill’. While various functions (e.g. foraging and hydrodynamic benefits) have been proposed for this structure, until now no study has directly investigated the mechanisms by which billfishes use their rostrum to feed on prey. Here, we present the first unequivocal evidence of how the bill is used by Atlantic sailfish (Istiophorus albicans) to attack schooling sardines in the open ocean. Using high-speed video-analysis, we show that (i) sailfish manage to insert their bill into sardine schools without eliciting an evasive response and (ii) subsequently use their bill to either tap on individual prey targets or to slash through the school with powerful lateral motions characterized by one of the highest accelerations ever recorded in an aquatic vertebrate. Our results demonstrate that the combination of stealth and rapid motion make the sailfish bill an extremely effective feeding adaptation for capturing schooling prey.

Although food deprivation is a major ecological pressure in fishes, there is wide individual variation in tolerance of fasting, whose mechanistic bases are poorly understood. Two thousand individually tagged juvenile European sea bass were submitted to two 'fasting/feeding' cycles each comprising 3 weeks of food deprivation followed by 3 weeks of ad libitum feeding at 25 degrees C. Rates of mass loss during the two fasting periods were averaged for each individual to calculate a population mean. Extreme fasting tolerant (FT) and sensitive (FS) phenotypes were identified that were at least one and a half standard deviations, on opposing sides, from this mean. Respirometry was used to investigate two main hypotheses: (1) tolerance of food deprivation reflects lower mass-corrected routine metabolic rate (RMR) in FT phenotypes when fasting, and (2) tolerance reflects differences in substrate utilisation; FT phenotypes use relatively less proteins as metabolic fuels during fasting, measured as their ammonia quotient (AQ), the simultaneous ratio of ammonia excretion to RMR. There was no difference in mean RMR between FT and FS over 7 days fasting, being 6.70 +/- 0.24 mmol h(-1) fish(-1) (mean +/- s.e.m., N=18) versus 6.76 +/- 0.22 mmol h(-1) fish(-1) (N=17), respectively, when corrected to a body mass of 130 g. For any given RMR, however, the FT lost mass at a significantly lower rate than FS, overall 7-day average being 0.72 +/- 0.05 versus 0.90 +/- 0.05 g day(-1) fish(-1), respectively (P

In intertidal environments, the recurring hypoxic condition at low tide is one of the main factors affecting fish behaviour, causing broad effects on ecological interactions. We assessed the effects of hypoxia on lateralization (e.g. the tendency to turn left or right), a behaviour related to brain functional asymmetry, which is thought to play a key role in several life history aspects of fish. Using staghorn sculpin (Leptocottus armatus), a benthic fish that typically inhabits the intertidal zone, we found that hypoxia affects behavioural lateralization at population-level. On average, staghorn sculpins showed a distinct preference for right turns under normoxic conditions (> 90 % oxygen saturation), but an equal probability of turning right or left after exposure to hypoxia for 2 hours (20 % oxygen saturation). The specific turning preference observed in the staghorn sculpin control population is likely to have an adaptive value, for example in predator-prey interactions by enhancing attack success or survival from predatory attacks. Therefore the alteration of lateralization expressed by staghorn sculpins under hypoxic conditions may have far-reaching implications for species ecology and trophic interactions. Moreover, our work raises the need to study this effect in other species, in which a hypoxia-driven disruption of lateralization could affect a wider range of behaviours, such as social interactions and schooling.

Summary Unsteady water flows are common in nature, yet the swimming performance of fishes is typically evaluated at constant, steady speeds in the laboratory. We examined how cyclic changes in water flow velocity affect the swimming performance and energetics of a labriform swimmer, the shiner surfperch, Cymatogaster aggregata. Using intermittent-flow respirometry, we measured critical swimming speed (Ucrit), oxygen consumption rate (ṀO2) and pectoral fin use in steady flow versus unsteady flows with either low (0.5 body lengths per second; BLs-1) or high amplitude (1.0 BLs-1) velocity fluctuations, with a 5 s period. Individuals in low amplitude unsteady flow performed as well as fish in steady flow. However, swimming costs in high amplitude unsteady flow were on average 25.3 % higher than in steady flow and 14.2% higher than estimated values obtained from simulations based on the non-linear relationship between swimming speed and oxygen consumption rate in steady flow. Time-averaged pectoral fin use (fin beat frequency measured over 300 s) was similar among treatments. However, measures of instantaneous fin use (fin beat period) and body movement in high amplitude unsteady flow indicate that individuals with greater variation in the duration of their fin beats were better at holding station and consumed less oxygen than fish with low variation in fin beat period. These results suggest that the costs of swimming in unsteady flows are context dependent in labriform swimmers, and may be influenced by individual differences in the ability of fishes to adjust their fin beats to the flow environment.

Summary Teleost fishes and mammalian lineages diverged 400 million years ago, and environmental requirements (water vs. air) have resulted in marked differences in cardiovascular function between fish and mammals. Suggestions that the fish secondary vascular system (SVS) could be used as a model for the mammalian lymphatic system should be taken with caution. Despite molecular markers indicating similar genetic origin, functions of the SVS in teleost fish are probably different from those of the mammalian lymphatic system. We determined that, in resting glass catfish, (Kryptopterus bicirrhis), plasma moves from the primary vascular system (PVS) to the SVS through small connecting vessels less than 10 μm in diameter, smaller than the red blood cells (RBCs). During and following hypoxia or exercise, flow increases, and RBCs enter the SVS, possibly via β-adrenoreceptor-mediated dilation of the connecting vessels. The volume of the SVS can be large and, as RBCs flow into the SVS, the haematocrit of the PVS falls by as much as 50% of the resting value. Possible functions of the SVS, including skin respiration, ionic and osmotic buffering, and reductions in heart work and RBC turnover, are discussed.

SummaryThere is considerable intraspecific variation in metabolic rates and locomotor performance in aquatic ectothermic vertebrates, however, the mechanistic basis remains poorly understood. Using pregnant Trinidadian guppies (Poecilia reticulata Peters), a live-bearing teleost, we examined effects of reproductive traits, pectoral fin use, and burst-assisted swimming on the swimming metabolic rate, standard metabolic rate (MO2std) and prolonged swimming performance (Ucrit). Reproductive traits (RT) included reproductive allocation and pregnancy stage; the former defined as the mass of the reproductive tissues divided by the total body mass. Results showed that the metabolic rate increased curvilinearly with swimming speed. The slope of the relationship was used as an index of swimming cost. There was no evidence that RT correlated with the swimming cost, MO2std, or Ucrit. In contrast, data revealed strong effects of pectoral fin use on swimming cost and Ucrit. P. reticulata employed body-caudal fin (BCF) swimming at all tested swimming speeds, however, fish with a high simultaneous use of the pectoral fins exhibited increased swimming cost and decreased Ucrit. These data indicated that combining BCF swimming and pectoral fin movement over a wide speed range, presumably to support swimming stability and control, is an inefficient swimming behaviour. Finally, transition to burst-assisted swimming was associated with an increase in aerobic metabolic rate. Our study highlights other factors than swimming speed affecting swimming cost and suggests that intraspecific diversity in biomechanical performance, such as pectoral fin use, is an important source of variation in both locomotor cost and maximal performance.

SUMMARY The contribution of air breathing to aerobic metabolic scope and exercise performance was investigated in a teleost with bimodal respiration, the banded knifefish, submitted to a critical swimming speed ( U crit ) protocol at 30°C. Seven individuals (mean ± s.e.m. mass 89±7 g, total length 230±4 mm) achieved a U crit of 2.1±1 body lengths (BL) s –1 and an active metabolic rate (AMR) of 350±21 mg kg –1 h –1 , with 38±6% derived from air breathing. All of the knifefish exhibited a significant increase in air-breathing frequency ( f AB ) with swimming speed. If denied access to air in normoxia, these individuals achieved a U crit of 2.0±0.2 BL s –1 and an AMR of 368±24 mg kg –1 h –1 by gill ventilation alone. In normoxia, therefore, the contribution of air breathing to scope and exercise was entirely facultative. In aquatic hypoxia ( P O 2 =4 kPa) with access to normoxic air, the knifefish achieved a U crit of 2.0±0.1 BL s –1 and an AMR of 338±29 mg kg –1 h –1 , similar to aquatic normoxia, but with 55±5% of AMR derived from air breathing. Indeed, f AB was higher than in normoxia at all swimming speeds, with a profound exponential increase during exercise. If the knifefish were denied access to air in hypoxia, U crit declined to 1.2±0.1 BL s –1 and AMR declined to 199±29 mg kg –1 h –1 . Therefore, air breathing allowed the knifefish to avoid limitations to aerobic scope and exercise performance in aquatic hypoxia.

Pop-up satellite archival tags (PSATs) have recently been applied in attempts to follow the oceanic spawning migration of the European eel. PSATs are quite large, and in all likelihood their hydraulic drag constitutes an additional cost during swimming, which remains to be quantified, as does the potential implication for successful migration. Silver eels (L(T)=598.6 +/- 29 mm SD, N = 9) were subjected to swimming trials in a Steffensen-type swim tunnel at increasing speeds of 0.3-0.9 body lengths s(-1), first without and subsequently with, a scaled down PSAT dummy attached. The tag significantly increased oxygen consumption (MO(2)) during swimming and elevated minimum cost of transport (COT(min)) by 26%. Standard (SMR) and active metabolic rate (AMR) as well as metabolic scope remained unaffected, suggesting that the observed effects were caused by increased drag. Optimal swimming speed (U(opt)) was unchanged, whereas critical swimming speed (U(crit)) decreased significantly. Swimming with a PSAT altered swimming kinematics as verified by significant changes to tail beat frequency (f), body wave speed (v) and Strouhal number (St). The results demonstrate that energy expenditure, swimming performance and efficiency all are significantly affected in migrating eels with external tags. Pop-up satellite archival tags (PSATs) have recently been applied in attempts to follow the oceanic spawning migration of the European eel. PSATs are quite large, and in all likelihood their hydraulic drag constitutes an additional cost during swimming, which remains to be quantified, as does the potential implication for successful migration. Silver eels (L(T)=598.6 +/- 29 mm SD, N = 9) were subjected to swimming trials in a Steffensen-type swim tunnel at increasing speeds of 0.3-0.9 body lengths s(-1), first without and subsequently with, a scaled down PSAT dummy attached. The tag significantly increased oxygen consumption (MO(2)) during swimming and elevated minimum cost of transport (COT(min)) by 26 Standard (SMR) and active metabolic rate (AMR) as well as metabolic scope remained unaffected, suggesting that the observed effects were caused by increased drag. Optimal swimming speed (U(opt)) was unchanged, whereas critical swimming speed (U(crit)) decreased significantly. Swimming with a PSAT altered swimming kinematics as verified by significant changes to tail beat frequency (f), body wave speed (v) and Strouhal number (St). The results demonstrate that energy expenditure, swimming performance and efficiency all are significantly affected in migrating eels with external tags.

Maternal size, age, and allostatic load influence offspring size, development, and survival. Some of these effects have been attributed to the release of glucocorticoids, and individual variation in these stress hormones is related to a number of traits. Correlated traits are often clustered and used to define the proactive and reactive stress coping styles. Although stress coping styles have been identified in a number of animal groups, little is known about the coupling between stress coping style and offspring characteristics. In the present study, plasma cortisol levels in ovulated mothers and cortisol levels in non-fertilized eggs from two rainbow trout (Oncorhynchus mykiss) strains selected for high (HR) and low (LR) post-stress plasma cortisol levels were compared. Offspring characteristics such as egg size, larval growth, and energy reserves also were compared between the two strains. Maternal plasma and egg cortisol levels were correlated, but no difference between the HR and LR strains was detected in either parameter. LR females produced larger eggs, and larvae with larger yolk sacs compared to HR females, however no differences in larval body size (excluding the yolk) was detected between strains. Considering that the HR and LR strains have a number of correlated behavioral and physiological traits that resemble the reactive and proactive stress coping styles, respectively, the results suggest that proactive mothers invest more energy into their offspring, producing larvae with larger energy reserves. It is possible that larger energy reserves in proactive larvae support the energy requirement for establishing and defending territory in salmonid fish. Furthermore, in the present study we found a positive relationship between mother plasma cortisol and egg cortisol; however neither mother plasma cortisol nor egg cortisol differed between strains. These results indicate that cortisol endowment from the mother to the offspring plays a minor role in the transfer of the behavioral and physiological traits which separates these strains.

Hypoxia-induced vascular responses, including angiogenesis, vascular remodeling and vascular leakage, significantly contribute to the onset, development and progression of retinopathy. However, until recently there were no appropriate animal disease models recapitulating adult retinopathy available. In this article, we describe protocols that create hypoxia-induced retinopathy in adult zebrafish. Adult fli1:EGFP zebrafish are placed in hypoxic water for 3-10 d and retinal neovascularization is analyzed using confocal microscopy. It usually takes 11 d to obtain conclusive results using the hypoxia-induced retinopathy model in adult zebrafish. This model provides a unique opportunity to study kinetically the development of retinopathy in adult animals using noninvasive protocols and to assess therapeutic efficacy of orally active antiangiogenic drugs.

Members of the family Embiotocidae exhibit a distinct gait transition from exclusively pectoral fin oscillation to combined pectoral and caudal fin propulsion with increasing swimming speed. The pectoral–caudal gait transition occurs at a threshold speed termed U p–c. The objective of this study was to partition aerobic and anaerobic swimming costs at speeds below and above the U p–c in the striped surfperch Embiotoca lateralis using swimming respirometry and video analysis to test the hypothesis that the gait transition marks the switch from aerobic to anaerobic power output. Exercise oxygen consumption rate was measured at 1.4, 1.9 and 2.3 L s–1. The presence and magnitude of excess post-exercise oxygen consumption (EPOC) were evaluated after each swimming speed. The data demonstrated that 1.4 L s–1 was below the U p–c, whereas 1.9 and 2.3 L s–1 were above the U p–c. These last two swimming speeds included caudal fin propulsion in a mostly steady and unsteady (burst-assisted) mode, respectively. There was no evidence of EPOC after swimming at 1.4 and 1.9 L s–1, indicating that the pectoral–caudal gait transition was not a threshold for anaerobic metabolism. At 2.3 L s–1, E. lateralis switched to an unsteady burst and flap gait. This swimming speed resulted in EPOC, suggesting that anaerobic metabolism constituted 25% of the total costs. Burst activity correlated positively with the magnitude of the EPOC. Collectively, these data indicate that steady axial propulsion does not lead to EPOC whereas transition to burst-assisted swimming above U p–c is associated with anaerobic metabolism in this labriform swimmer. * COT : cost of transport EPOC : excess post-exercise oxygen consumption f b : burst frequency f c : caudal fin beat frequency f p : pectoral fin beat frequency L F : fork length L S : standard length ![Graphic][1] : oxygen consumption rate RMR : routine metabolic rate U : swimming speed U crit : critical swimming speed U opt : optimum swimming speed U p–c : pectoral–caudal gait transition speed [1]: /embed/inline-graphic-32.gif

The influence of prolonged moderate (c. 60% oxygen saturation) and severe hypoxia (c. 35% oxygen saturation) on the diurnal activity pattern of sandeel Ammodytes tobianus was examined. In moderate hypoxia, the emerging and burying rates were significantly higher compared to that in normoxia, whereas fewer fish (c. 10%) were present in the water column. In contrast, severe hypoxia resulted in twice as many or more fish being present in the water column compared to that in normoxia. The increased number of swimming fish was not just a relative change due to an effect from hypoxia treatment, but the behaviour of the fish was also changed. The summed activity (emerging plus burying events) was lower in severe hypoxia compared to normoxia except during hours of dim light. All fish were buried during night-time, regardless of treatment, with the exception of some in severe hypoxia during the first couple of hours of darkness.

This study examines stress responses in Atlantic cod (Gadus morhua) when exposed to a moderate and transient reduction (35% O(2) sat.) in dissolved oxygen at a range of temperatures (5 degrees C, 10 degrees C and 15 degrees C), conditions occurring in some areas they inhabit. Given their geographical distribution pattern, and differences in preferred temperature of cod with different haemoglobin types, the study was extended to include haemoglobin polymorphism. We hypothesised that the differences in temperature preference between HbI-1 and HbI-2 type cod might also be reflected in a difference in stress response to hypoxia exposure. Two hsp70-isoforms (labelled a and b) were detected and they differed in expression in the gills but not in the liver of Atlantic cod. Acclimation temperature significantly affected the expression of hsp70 in the liver, and in an isoform-specific manner in the gills. Hypoxia exposure increased the expression of hsp70 in the liver, but not the gills, of cod and this response was not influenced by the acclimation temperature. The expression of hsp70 in both tissues did not differ between fish with different haemoglobin types. Acclimation temperature significantly impacted plasma cortisol but not lactate levels. Also, acute oxygen limitation or HbI-type significantly elevated plasma cortisol and lactate levels but these responses were not modulated by acclimation temperature. Taken together, our results suggest that both temperature acclimation and acute hypoxic exposure influence the organismal and cellular stress responses in Atlantic cod. We hypothesise that HbI-2 fish are more tolerant to short-term hypoxic episodes than HbI-1 fish, and this adaptation may be independent of tissue hsp70 expression.