Group swimming behaviour and energetics in bluegill Lepomis macrochirus and rainbow trout Oncorhynchus mykiss

Group swimming size influences metabolic energy consumption and swimming behaviour in fishes. Hydrodynamic flows and vortices of other fish are thought to be beneficial in terms of the energetic costs of swimming. Similarly, abiotic obstructions have been shown to have similar benefits with respect to metabolic consumption in swimming fish such as rainbow trout Oncorhynchus mykiss. The current study works to examine metabolic rates and swimming behaviours as a function of group swimming with bluegill sunfish Lepomis macrochirus and O. mykiss. Fishes were subjected to individual and group swimming in a respiratory swim tunnel to determine oxygen consumption as a proxy for the metabolic rate of swimming fish. In addition, fish movements within the swim tunnel test chamber were tracked to examine group swimming behaviour. We hypothesized that fish would benefit metabolically from group swimming. In the case of O. mykiss, we also hypothesized that groups would benefit from the presence of an abiotic structure, as has been previously observed in fish swimming individually. Our results suggest that the influence of group size on swimming metabolism is species specific. While L. macrochirus show decreased metabolic rate when swimming in a group compared to individually, O. mykiss did not show such a metabolic benefit from group swimming.     

Rainbow trout display a developmental shift in red muscle kinetics, swimming kinematics and myosin heavy chain isoform

Both activation and relaxation times of rainbow trout Oncorhynchus mykiss red muscle were shorter in parr than in older juveniles. Furthermore, parr red muscle had a faster maximum shortening velocity than that of older fish, as estimated with the force-clamp technique. Parr swam with higher tailbeat frequencies and lower tailbeat amplitude than did older fish across a range of length-specific steady swimming speeds. The developmental shift in contraction kinetics of red muscle and steady swimming kinematics was associated with a reduction from two or three myosin heavy chain isoforms in parr to one in older juveniles. This transition provides a mechanism to explain the variations in muscle contraction kinetics and swimming performance.     

Swimming performance, venous oxygen tension and cardiac performance of coronary-ligated rainbow trout, Oncorhynchus mykiss, exposed to progressive hypoxia

We performed in vivo studies to examine the idea that cardiac work is impaired in rainbow trout (Oncorhynchus mykiss) below a certain venous PO2 threshold. We hypothesized that coronary-ligated fish, swimming continuously at a reasonably high water velocity (1.5 body lengths x s(-1)) and exposed to progressive hypoxia, would fatigue at higher venous PO2 and ambient water PO2 compared with sham-operated fish. However, we found that both the lowest venous PO2 that supported hypoxic swimming (9.9 torr for coronary-ligated fish and 11.1 torr for sham-operated fish) and the venous PO2 at fatigue (7.8 torr and 8.6 torr, respectively) were the same for coronary-ligated and sham-operated fish. Also, both groups quit swimming at the same water PO2 heart rate and hematocrit. Nevertheless, significant differences in cardiac performance did exist between the two groups. Whereas ventral aortic blood pressure (Pva) increased significantly with hypoxic swimming in sham-operated fish, there was no such increase in coronary-ligated fish. In addition, cardiac arrhythmias occurred in coronary-ligated fish at fatigue, and these fish were slower to recover from exhaustion. We believe that the venous PO2 threshold to support cardiac performance in the absence of a coronary supply was between 7.8 and 9.9 torr. Furthermore, we suspect that the low PO2 in coronary-ligated fish effectively lowered their myocardial O2 demand. Uncertainty still exists regarding whether or not the venous PO2 threshold lies between 8.6 and 11.1 torr in sham-operated fish.     

Group size influences foraging effort independent of predation risk: an experimental study on rainbow trout

Foraging effort, swimming activity, vertical position and flight response were recorded in focal juvenile rainbow trout Oncorhynchus mykiss at three group sizes: without company, or in visual and chemical contact with either one or five companion fish at two levels of predation risk: high (simulated aerial predator attack) or low (no attack). The predator attack induced a pronounced flight reaction as well as a reduction in vertical position, feeding and swimming activity. The foraging effort of the focal fish increased with group size independent of the level of predation risk, which suggests that the group-mediated increase in foraging activity is caused by competition rather than by reduction in perceived risk. The flight response to the predator attack, however, was stronger when the focal fish had company, suggesting that individuals may benefit from copying the anti-predator response of other group members.     

Subclinical Listonella anguillarum infection does not impair recovery of swimming performance in rainbow trout Oncorhynchus mykiss

This study examines whether injections of the commonly used bacterial-challenge pathogen Listonella anguillarum (formerly Vibrio anguillarum) negatively impact the ability of rainbow trout Oncorhynchus mykiss Walbaum to perform repeat swimming trials. Fish were given intraperitoneal injections of either a sub-lethal (10(5) colony forming units; CFUs) or a lethal (10(7) CFUs) dose of L. anguillarum, held for 48 h, and then given 2 successive ramp critical swimming speed (Ucrit) tests separated by 45 min. Compared with saline-injected control fish, the low-dose injection did not significantly impair swimming performance and recovery. Similarly, Ucrit and re-performance for fish surviving the high-dose injection were comparable to control (2 of 6 fish died after injection and before testing). In contrast, a positive control test of seawater challenge did impair recovery of swimming performance. In view of these results and common use of L. anguillarum as a challenge pathogen for toxicological studies, it seems unlikely that the consequences of pathogenesis impact the important cardiorespiratory changes associated with exercise.     

Constraints of body size and swimming velocity on the ability of juvenile rainbow trout to endure periods without food

The hypothesis that body size and swimming velocity affect proximate body composition, wet mass and size‐selective mortality of fasted fish was evaluated using small (107 mm mean total length, L _T) and medium (168 mm mean L _T) juvenile rainbow trout Oncorhynchus mykiss that were sedentary or swimming ( c . 1 or 2 body length s⁻¹) and fasted for 147 days. The initial amount of energy reserves in the bodies of fish varied with L _T. Initially having less lipid mass and relatively higher mass‐specific metabolic rates caused small rainbow trout that were sedentary to die of starvation sooner and more frequently than medium‐length fish that were sedentary. Swimming at 2 body length s⁻¹ slightly increased the rate of lipid catabolism relative to 1 body length s⁻¹, but did not increase the occurrence of mortality among medium fish. Death from starvation occurred when fish had <3·2% lipid remaining in their bodies. Juvenile rainbow trout endured long periods without food, but their ability to resist death from starvation was limited by their length and initial lipid reserves.     

Anaemia and salmonid swimming performance: the potential effects of sub‐lethal sea lice infection

The effect of two known rates of repeated blood loss on rainbow trout Oncorhynchus mykiss swimming performance was measured and blood‐feeding rates of sea lice Lepeophtheirus salmonis were calculated to predict the point at which blood ingestion causes anaemia in infected fish. Known quantities of blood were sampled from rainbow trout over a 5 day period followed by critical swimming performance ( U _crit) testing. A predictive equation was developed using masses of blood‐feeding sea lice and host blood loss calculated for increasing levels of sea lice infection. Blood loss of 8% total blood volume caused a decrease in U _crit for rainbow trout. Total blood volume losses of 3·2% reduced erythrocyte stores, but did not affect fish swimming performance. The predictive feeding rate model suggests that 15–25% of the tissue consumed by sea lice is blood. This consumption of blood at higher sub‐lethal infection levels (≥0·5 sea lice g⁻¹) may cause anaemia and a further decrease in swimming performance. Anaemia would compound the osmotic balance problems due to infection and potentially precipitate the morbidity seen at lethal sea lice levels (0·75–1·0 lice g⁻¹).     

Physiological and Endocrinological Responses During Prolonged Exercise in Hatchery-Reared Rainbow Trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) were subjected to vigorous exercise (1.5 body length s−1), low exercise (0.5 body length s−1) or still-water (0.0 body length s−1). Hematocrit, glucose, growth hormone (GH), Cortisol and triiodo-L-thyronine (T3) were monitored at the start of exercise, after 24 h, and after 2, 4, 8, 16 and 32 days of continuous swimming. Morphological indices and food intake were also monitored. At the end of the experiment, trout subjected to low exercise had gained significantly (p<0.05) more weight than both the control (still-water) and vigorously exercised fish. This low exercised group of fish also consumed more food than the 2 other groups. Hematocrit increased significantly in both exercised groups at the onset of swimming but returned to pre-exercise levels within 8 hrs. Plasma glucose appeared to be generally unaffected by exercise. Likewise, plasma concentrations of both GH and T3 were not influenced by exercise. Plasma Cortisol levels increased in an exercise dependent fashion at the onset of swimming, but returned to pre-swimming levels within 24 h and there was no apparent effect of sustained swimming. The results suggest: (i) the onset of exercise elicits transient changes in plasma components, (ii) the observed weight gain in low exercising salmonids occur without increases in circulating levels of GH or T3.     

The recovery of locomotory activity following exhaustive exercise in juvenile rainbow trout (Oncorhynchus mykiss)

This study investigated the recovery of locomotory activity in exhausted juvenile rainbow trout (Oncorhynchus mykiss, approximately 6-10-cm fork length) in response to two conditions: (1) direct transfer to a range of velocities (0-15 cm s(-1)) in a swim flume (forced swimming) and (2) direct transfer to a pool downstream of a swim channel where a choice of velocities was presented: 2-3 cm s(-1) in the lower half of the pool, a range of velocities from 7 to 40 cm s(-1) in the upper half the pool near the channel entrance, and a velocity of 57 cm s(-1) in a swim channel emptying into the pool (volitional swimming). Exhausted trout showed a pronounced delay in the recovery of normal locomotory activity. With forced swimming, the time required to resume swimming was inversely proportional to water velocity. At 15 cm s(-1), almost all exhausted fish recovered immediately, whereas it took about 1 h for recovery at a current of 5 cm s(-1). In contrast, nonexhausted fish responded to imposed velocity with immediate rheotactic responses (orientation and station holding) at all test velocities. In voluntary swim trials, exhausted trout showed a marked preference for holding station in current in the downstream pool (approximately 11 cm s(-1)) but took, on average, 2 h longer than nonexhausted fish to make transits in the swim channel. Moreover, their ground speed in the swim channel was significantly slower. We conclude that swimming performance is impaired for at least 6 h by exhaustive exercise. Maladaptive behaviors during this time include a preference for current near the surface over cover and a reduced capacity for burst activity, both of which would translate into greater predation risk and reduced ability to forage.     

Magnetic field perception in the rainbow trout Oncorynchus mykiss: magnetite mediated, light dependent or both?

In the present study, we demonstrate the role of the trigeminal system in the perception process of different magnetic field parameters by heartbeat conditioning, i.e. a significantly longer interval between two consecutive heartbeats after magnetic stimulus onset in the salmonid fish Oncorhynchus mykiss. The electrocardiogram was recorded with subcutaneous silver wire electrodes in freely swimming fish. Inactivation of the ophthalmic branch of the trigeminal nerve by local anaesthesia revealed its role in the perception of intensity/inclination of the magnetic field by abolishing the conditioned response (CR). In contrast, experiments with 90° direction shifts clearly showed the normal conditioning effect during trigeminal inactivation. In experiments under red light and in darkness, CR occurred in case of both the intensity/inclination stimulation and 90° direction shifts, respectively. With regard to the data obtained, we propose the trigeminal system to perceive the intensity/inclination of the magnetic field in rainbow trouts and suggest the existence of another light-independent sensory structure that enables fish to detect the magnetic field direction.     

Sub-lethal plasma ammonia accumulation and the exercise performance of salmonids

The proposal that plasma ammonia accumulation might impair the swimming performance of fish was first made over a decade ago, and has now proven to be the case for a number of salmonid species. The first experimental evidence was indirect, when a negative linear relationship between plasma ammonia concentrations and maximum sustainable swimming speed (U(crit)) was found following the exposure of brown trout (Salmo trutta) to sub-lethal concentrations of copper in soft acidic water. Since then, negative linear relationships between plasma ammonia concentration and U(crit) have been demonstrated following exposure of brown trout, rainbow trout (Oncorhynchus mykiss) and coho salmon (Oncorhynchus kisutch) to elevated water ammonia. For brown trout, the relationships between plasma ammonia and U(crit) were remarkably similar following either exposure to elevated water ammonia or to sub-lethal copper. This indicates that the impairment of swimming performance resulting from exposure to sub-lethal concentrations of heavy metals may be attributable in large part to an accumulation of endogenous ammonia. The negative relationship between plasma ammonia concentration and U(crit) was similar in size-matched rainbow and brown trout but, under similar regimes of ammonia exposure, rainbow trout were able to maintain a significantly lower plasma ammonia concentration, revealing inter-specific differences in ammonia permeability and/or transport. One primary mechanism by which ammonia accumulation may impair exercise performance is a partial depolarisation of membrane potential in tissues such as the brain and white muscle. This may prejudice the co-ordination of swimming movements and reduce or abolish the development of muscle tension, thus, compromising swimming efficiency and performance at the top end of the range.     

Behaviour of rainbow trout Oncorhynchus mykiss presented with a choice of normoxia and stepwise progressive hypoxia

The objective of this study was to identify behavioural adjustments leading to avoidance of hypoxia. Using the oxygen-sensitive species rainbow trout Oncorhynchus mykiss as a model, individual fish were recorded while moving freely between two sides of a test arena: one with normoxia and one with stepwise progressive hypoxia [80-30% dissolved oxygen (DO) air saturation]. The results demonstrated a gradual decrease in the total time spent in hypoxia starting at 80% DO air saturation. At this DO level, the avoidance of hypoxia could not be attributed to changes in spontaneous swimming speed, neither in normoxia nor in hypoxia. Reducing the DO level to 60% air saturation resulted in decreased spontaneous swimming speed in normoxia, yet the number of trips to the hypoxic side of the test arena remained unchanged. Moreover, data revealed increased average residence time per trip in normoxia at DO levels ≤60% air saturation and decreased average residence time per trip in hypoxia at DO levels ≤50% air saturation. Finally, the spontaneous swimming speed in hypoxia increased at DO levels ≤40% air saturation and the number of trips to hypoxia decreased at the 30% DO air saturation level. Thus, avoidance of the deepest hypoxia was connected with a reduced number of trips to hypoxia as well as decreased and increased spontaneous swimming speed in normoxia and hypoxia, respectively. Collectively, the data support the conclusions that the mechanistic basis for avoidance of hypoxia may (1) not involve changes in swimming speed during mild hypoxia and (2) depend on the severity of hypoxia.     

Non-invasive recording of heart rate and ventilation rate in rainbow trout during rest and swimming. Fish go wireless!

Resting heart rates and ventilation rates in rainbow trout Oncorhynchus mykiss at 15°C are 31·8±1·8 beat min⁻¹ and 53·1±3·7 breaths min⁻¹, respectively. The non-invasive recording system picked up the bioelectric potentials generated by the fish in the water and was based on an array of six silver-silver chloride electrodes covered with agar-gel, which provided a better signal-to-noise ratio than in previously described systems, and allowed the determination of heart rate and ventilation rates at different swimming speeds up to 21 s⁻¹. In concert with the lower rates, the scope for changes in heart rate and ventilation rate during swimming was also considerably larger than in earlier studies (2·4- and 2·0-fold, respectively). Two main conclusions result from this work: (i) short recovery times under 48 h after anaesthesia and surgery are unlikely to provide truly resting heart rates and ventilation rates in trout at 15°C; (ii) heart rate regulation during exercise is more important than previously thought and might account for a larger proportion of the increase in cardiac output observed in swimming trout.     

Variability in swimming performance and underlying physiology in rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta)

We investigated intra- and interspecific variation in swimming performance and related physiological parameters in two members of the salmonid family. For our comparisons, we sourced juvenile brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) from one hatchery and a second strain of rainbow trout from another. The hatcheries maintain genetic stocks obtained several decades ago from very different environments. We tested competing hypotheses: that there would be greater interspecific (across species) variation or that there would be greater intraspecific (within species) variation, owing to regional adaptations. To test these hypotheses, individual and small schools of five fish were taken to fatigue using the critical swimming speed test (U(crit)), and three post-exercise physiological metrics, packed red cell volume (hematocrit), citrate synthase and lactate dehydrogenase activity, were assessed. The majority of the results in swimming performance and hematocrit support that intraspecific variation was greater than interspecific variation, i.e. the location had a stronger effect than did genus. Variation in lactate dehydrogenase activity supported neither intra- nor interspecific variation as determining factors. In sum, our findings suggest that the performance of different species of salmonids from the same locale can be more similar than those of the same species from different areas.     

What information do Kármán streets offer to flow sensing?

In this work, we focus on biomimetic lateral line sensing in Kármán vortex streets. After generating a Kármán street in a controlled environment, we examine the hydrodynamic images obtained with digital particle image velocimetry (DPIV). On the grounds that positioning in the flow and interaction with the vortices govern bio-inspired underwater locomotion, we inspect the fluid in the swimming robot frame of reference. We spatially subsample the flow field obtained using DPIV to emulate the local flow around the body. In particular, we look at various sensor configurations in order to reliably identify the vortex shedding frequency, wake wavelength and downstream flow speed. Moreover, we propose methods that differentiate between being in and out of the Kármán street with >70% accuracy, distinguish right from left with respect to Kármán vortex street centreline (>80%) and highlight when the sensor system enters the vortex formation zone (>75%). Finally, we present a method that estimates the relative position of a sensor array with respect to the vortex formation point within 15% error margin.     

Trophic interactions among native and introduced fishes in a northern Patagonian oligotrophic lake

In summer the littoral zone of Lake Rivadavia contained almost all the juveniles of the native fish species present in the lake together with juveniles of the introduced salmonid Oncorhynchus mykiss . In particular, a high degree of foraging interaction was found among juveniles of the native species Aplochiton zebra and Percichthys trucha and juveniles O. mykiss. Differences in the juvenile assemblage composition, both in the presence and in the relative proportion of the species were associated with areas with different densities of vegetation. The adults of nearly all species were generalized benthic invertebrate predators. Only adults of A. zebra were absent in the littoral. Juvenile and adult O. mykiss were the only fish that preyed on planktonic organisms. Oncorhynchus mykiss was the only species that performed an ontogenetic diet shift between juveniles and adults, changing main prey categories from benthic to planktonic species.     

Exhaustive exercise does not affect the preferred temperature for recovery in juvenile rainbow trout (Oncorhynchus mykiss)

We tested the hypothesis that juvenile rainbow trout (Oncorhynchus mykiss) would select a temperature colder than their acclimation temperature (16 deg +/-1 deg C) to minimize postexhaustive exercise metabolic demands and enhance oxygen availability. After an initial 3-h exploratory period in a thermal gradient (6 degrees -25 degrees C), fish selected a temperature of approximately 14 degrees C and had a baseline exploratory swimming activity of approximately 60 cm min(-1). Subsequently, experimental (chased) fish were individually removed, exhaustively exercised for 1.5 min, and replaced. Both control (unchased) and experimental fish were allowed to explore the thermal gradient for another 2 h. Immediately after being chased, trout had a metabolic profile that was consistent with being exhausted; levels of plasma and muscle lactate were 4.38+/-0.25 mmol L(-1) and 28.0+/-2.0 mmol kg(-1), respectively, and levels of muscle glycogen, adenosine triphosphate, and phosphocreatine were 3.89+/-0.95, 4.23+/-0.62, and 3.07+/-0.73 mmol kg(-1), respectively. Although exploratory swimming activity of the chased fish was significantly lower (by 81%) as compared with control fish during the first 5 min postchase, differences in the mean, median, and mode values for selected temperatures during the next 2 h were neither large (<1 degrees C) nor significant (P>0.05). Contrary to our initial hypothesis, these findings suggest that juvenile rainbow trout do not select a colder temperature to decrease metabolic rate following exhaustive exercise. Instead, rainbow trout selected a temperature marginally cooler than their acclimation temperature (16 degrees C) regardless of whether they had been previously exhausted.     

Assessment of cardiac output as a predictor of metabolic rate in rainbow trout

When water temperature was increased from 12 to 27°C at a rate of 2°C h⁻¹, oxygen consumption of rainbow trout Oncorhynchus mykiss was correlated strongly with both heart rate and blood oxygen extraction but the relationship with cardiac output was variable and weak. On the other hand, when water temperature was decreased from 21 to 12°C at a rate of 0·5°C h⁻¹, oxygen consumption was correlated with both heart rate and cardiac output but not with blood oxygen extraction. When fish were forced to swim increasingly faster, heart rate, cardiac output and blood oxygen extraction all correlated positively with oxygen consumption. For both cardiac output and heart rate, the slope of the regression line with oxygen consumption was elevated significantly more when the fish were forced to swim at increasingly higher swimming speeds than when water temperature was increased or decreased. The variation of the regression lines between cardiac output and oxygen consumption indicated that cardiac output presents few advantages over heart rate as a predictor of metabolic rate.     

Use of a self-propelled,fish-shaped,computer model to study the effects of shape and tail-beat frequency on torque and velocity in salmon-shaped fish

The relationship between fish shape, swimming ability and energy consumption during swimming in fish is complex and not well understood. In this paper, we show how a self-propelled 3-D fish model can be used to examine the effect of controlled changes in some shape parameters. Parameters of the model fish are modified and the resulting fish activated for short swimming episodes during which swimming velocity, torque and energy expenditure are calculated in the computer environment. The effect of shape was determined for two different fish shapes swimming at three different tail-beat frequencies (1.43, 0.94 and 0.64?Hz). The simulation results indicate that fish model one (based on a salmon) has stronger swimming ability than fish model two (a modified salmon fish shape) even though energy expenditure of fish shape two is greater than that of fish shape one. In the same fish types, the fish-swimming velocity and energy expenditure are proportional to tail-beat frequency. This model has the potential to be useful, particularly for predicting fish behavior in fish swim ways and the tail-water of energy turbines.