Intermittent propulsion in largemouth bass, Micropterus salmoides, increases power production at low swimming speeds.

Locomotion dominates animal energy budgets, and selection should favour behaviours that minimize transportation costs. Recent fieldwork has altered our understanding of the preferred modes of locomotion in fishes. For instance, bluegill employ a sustainable intermittent swimming form with 2-3 tail beats alternating with short glides. Volitional swimming studies in the laboratory with bluegill suggest that the propulsive phase reflects a fixed-gear constraint on body-caudal-fin activity. Largemouth bass (Micropterus salmoides) also reportedly display intermittent swimming in the field. We examined swimming by bass in a static tank to quantify the parameters of volitional locomotion, including tailbeat frequency and glide duration, across a range of swimming speeds. We found that tailbeat frequency was not related to speed at low swimming speeds. Instead, speed was a function of glide duration between propulsive events, with glide duration decreasing as speed increased. The propulsive Strouhal number remained within the range that maximizes propulsive efficiency. We used muscle mechanics experiments to simulate power production by muscle operating under intermittent versus steady conditions. Workloop data suggest that intermittent activity allows fish to swim efficiently and avoid the drag-induced greater energetic cost of continuous swimming. The results offer support for a new perspective on fish locomotion: intermittent swimming is crucial to aerobic swimming energetics.

Swimming from coast to coast: a novel fixed-gear swimming gait in fish.

Bluegill sunfish use intermittent propulsion during volitional swimming. The function of this propulsive mode during routine swimming has not been well quantified. At low speeds, propulsive cycle frequencies and amplitudes were constant, and average speed and power output were controlled by modulating coasting duration. This fixed-gear gait may accommodate muscle level constraints on power production. At higher speeds bluegills switched to a mixed power-modulation strategy, increasing speed and power through increased propulsive cycle frequency and reduced coasting time.

Variation in the diet and feeding morphology of polyphenic Lepomis macrochirus.

Bluegill Lepomis macrochirus showed variation in their diet and trophic morphology based on habitat. Pelagic L. macrochirus feed almost exclusively on cladocerans; littoral L. macrochirus feed on a variety of benthic invertebrates, molluscs, cladocerans and insects. Fish from the littoral habitat had wider pharyngeal jaws, which probably allowed them to crush gastropods and process benthic invertebrates.

A new approach to quantifying morphological variation in bluegill Lepomis macrochirus.

Bluegill Lepomis macrochirus showed intraspecific morphological and behavioural differences dependent on the environment. Pelagic L. macrochirus had more fusiform bodies, a higher pectoral fin aspect ratio, a larger spiny dorsal fin area and pectoral fins located farther from the centre of mass than littoral L. macrochirus (P < 0·05). The shape of the body and pectoral fins, in particular, were suggestive of adaptation for sustained high-speed and economical labriform swimming. Littoral L. macrochirus had a deeper and wider body, deeper caudal fins and wider mouths than pelagic L. macrochirus (P < 0·05). Additionally, the soft dorsal, pelvic, anal and caudal fins of littoral L. macrochirus were positioned farther from the centre of mass (P < 0·05). The size and placement of these fins suggested that they will be effective in creating turning moments to facilitate manoeuvring in the macrophyte-dense littoral habitat.

The effects of acute temperature change on cost of transport at maximal labriform speed in bluegill Lepomis macrochirus.

The effects of acute temperature change on the cost of bluegill Lepomis macrochirus swimming were quantified. At 14 degrees C, maximum labriform swimming speed (U(lab,max)) was reduced relative to that at the acclimation temperature of 22 degrees C, but total cost of transport (T(TC)) remained unchanged. At 30 degrees C, U(lab,max) was the same as at 22 degrees C, but T(TC) was 66% greater.

The mechanical power requirements of avian flight.

A major goal of flight research has been to establish the relationship between the mechanical power requirements of flight and flight speed. This relationship is central to our understanding of the ecology and evolution of bird flight behaviour. Current approaches to determining flight power have relied on a variety of indirect measurements and led to a controversy over the shape of the power-speed relationship and a lack of quantitative agreement between the different techniques. We have used a new approach to determine flight power at a range of speeds based on the performance of the pectoralis muscles. As such, our measurements provide a unique dataset for comparison with other methods. Here we show that in budgerigars (Melopsittacus undulatus) and zebra finches (Taenopygia guttata) power is modulated with flight speed, resulting in U-shaped power-speed relationship. Our measured muscle powers agreed well with a range of powers predicted using an aerodynamic model. Assessing the accuracy of mechanical power calculated using such models is essential as they are the basis for determining flight efficiency when compared to measurements of flight metabolic rate and for predicting minimum power and maximum range speeds, key determinants of optimal flight behaviour in the field.

ISOFIT: a model-based method to measure muscle-tendon properties simultaneously.

Estimation of muscle parameters specifying force-length and force-velocity behavior requires in general a large number of sophisticated experiments often including a combination of isometric, isokinetic, isotonic, and quick-release experiments. This study validates a simpler method (ISOFIT) to determine muscle properties by fitting a Hill-type muscle model to a set of isovelocity data. Muscle properties resulting from the ISOFIT method agreed well with muscle properties determined separately in in vitro measurements using frog semitendinosus muscles. The force-length curve was described well by the results of the model. The force-velocity curve resulting from the model coincided with the experimentally determined curve above approximately 20% of maximum isometric force (correlation coefficient R>0.99). At lower forces and thus higher velocities the predicted curve underestimated velocity. The stiffness of the series elastic component determined with direct experiments was approximately 10% lower than that determined by the ISOFIT method. Use of the ISOFIT method can decrease experimental time up to 80% and reduce potential changes in muscle parameters due to fatigue.

Spatial variation in fast muscle function of the rainbow trout Oncorhynchus mykiss during fast-starts and sprinting.

Fish fast-starts and sprints are rapid kinematic events powered by the lateral myotomal musculature. A distinction can be made between fast-starts and sprint-swimming activity. Fast-starts are kinematic events involving rapid, asymmetrical movements. Sprints involve a series of symmetrical, high-frequency tailbeats that are kinematically similar to lower-frequency, sustained swimming. The patterns of muscle recruitment and strain associated with these swimming behaviours were determined using electromyography and sonomicrometry. Axial patterns of fast muscle recruitment during sprints were similar to those in slow muscle in that the duration of electromyograhic (EMG) activity decreased in a rostro-caudal direction. There was also an axial shift in activity relative to the strain cycle so that activity occurred relatively earlier in the caudal region. This may result in caudal muscle performing a greater proportion of negative work and acting as a power transmitter as well as a power producer. The threshold tailbeat frequency for recruitment of fast muscle differed with location in the myotome. Superficial muscle fibres were recruited at lower tailbeat frequencies and shortening velocities than those deeper in the musculature. During sprints, fast muscle strain ranged from +/- 3.4% l(0) (where l(0) is muscle resting length) at 0.35FL (where FL is fork length) to +/- 6.3% l(0) at 0.65FL. Fast-starts involved a prestretch of up to 2.5% l(0) followed by shortening of up to 11.3% l(0). Stage 1 EMG activity began simultaneously, during muscle lengthening, at all axial locations. Stage 2 EMG activity associated with the major contralateral contraction also commenced during lengthening and proceeded along the body as a wave. Onset of muscle activity during lengthening may enhance muscle power output.

Fast muscle function in the European eel (Anguilla anguilla L.) during aquatic and terrestrial locomotion.

Eels are capable of locomotion both in water and on land using undulations of the body axis. Axial undulations are powered by the lateral musculature. Differences in kinematics and the underlying patterns of fast muscle activation are apparent between locomotion in these two environments. The change in isometric fast muscle properties with axial location was less marked than in most other species. Time from stimulus to peak force (T(a)) did not change significantly with axial position and was 82+/-6 ms at 0.45BL and 93+/-3 ms at 0.75BL, where BL is total body length. Time from stimulus to 90% relaxation (T(90)) changed significantly with axial location, increasing from 203+/-11ms at 0.45BL to 239+/-9 ms at 0.75BL. Fast muscle power outputs were measured using the work loop technique. Maximum power outputs at +/-5% strain using optimal stimuli were 17.3+/-1.3W kg(-1) in muscle from 0.45BL and 16.3+/-1.5W kg(-1) in muscle from 0.75BL. Power output peaked at a cycle frequency of 2Hz. The stimulus patterns associated with swimming generated greater force and power than those associated with terrestrial crawling. This decrease in muscle performance in eels may occur because on land the eel is constrained to a particular kinematic pattern in order to produce thrust against an underlying substratum.

Slow muscle power output of yellow- and silver-phase European eels (Anguilla anguilla L.): changes in muscle performance prior to migration.

Eels swim in the anguilliform mode in which the majority of the body axis undulates to generate thrust. For this reason, muscle function has been hypothesised to be relatively uniform along the body axis relative to some other teleosts in which the caudal fin is the main site of thrust production. The European eel (Anguilla anguilla L.) has a complex life cycle involving a lengthy spawning migration. Prior to migration, there is a metamorphosis from a yellow (non-migratory) to a silver (migratory) life-history phase. The work loop technique was used to determine slow muscle power outputs in yellow- and silver-phase eels. Differences in muscle properties and power outputs were apparent between yellow- and silver-phase eels. The mass-specific power output of silver-phase slow muscle was greater than that of yellow-phase slow muscle. Maximum slow muscle power outputs under approximated in vivo conditions were 0.24 W kg(-1) in yellow-phase eel and 0.74 W kg(-1) in silver-phase eel. Power output peaked at cycle frequencies of 0.3--0.5 Hz in yellow-phase slow muscle and at 0.5--0.8 Hz in silver-phase slow muscle. The time from stimulus offset to 90 % relaxation was significantly greater in yellow- than in silver-phase eels. The time from stimulus onset to peak force was not significantly different between life-history stages or axial locations. Yellow-phase eels shifted to intermittent bursts of higher-frequency tailbeats at a lower swimming speed than silver-phase eels. This may indicate recruitment of fast muscle at low speeds in yellow-phase eels to compensate for a relatively lower slow muscle power output and operating frequency.

Slow muscle function of Pacific bonito (Sarda chiliensis) during steady swimming.

The Pacific bonito, Sarda chiliensis, is anatomically intermediate between mackerel and tuna. The specialisations exhibited by tuna are present in the bonito, but to a lesser degree. Slow-twitch muscle strain and activity patterns were determined during steady swimming (tailbeat frequency 1.2-3.2 Hz) at four locations on the body of Sarda chiliensis using sonomicrometry and electromyography. Both strain and the phase of electromygraphic activity were independent of tailbeat frequency. The strain of superficial slow-twitch muscle increased from +/-3.1 % l(0) at 0.35FL to +/-5.8 % l(0) at 0.65FL, where l(0) is muscle resting length and FL is the body length from snout to tail fork. Between 0.35 and 0.65FL, there was a negative phase shift of 16 degrees in the onset of electromygraphic activity in superficial slow-twitch muscle relative to the strain cycle. Muscle activity patterns are comparable with those of tuna. At 0.58FL, the onset of activity in deep slow-twitch muscle was approximately synchronous with the onset of activity in superficial muscle in the same myotome at 0.65FL. The distribution of slow-twitch muscle along the body of Sarda chiliensis and four additional fish species, Anguilla anguilla, Oncorhynchus mykiss, Scomber scombrus and Thunnus albacares, was also measured. Slow-twitch muscle appears to become more concentrated at approximately 0.5FL as swimming kinematics become more thunniform.

Fish swimming: patterns in muscle function.

Undulatory swimming in fish is powered by the segmental body musculature of the myotomes. Power generated by this muscle and the interactions between the fish and the water generate a backward-travelling wave of lateral displacement of the body and caudal fin. The body and tail push against the water, generating forward thrust. The muscle activation and strain patterns that underlie body bending and thrust generation have been described for a number of species and show considerable variation. This suggests that muscle function may also vary among species. This variation must be due in large part to the complex interactions between muscle mechanical properties, fish body form, swimming mode, swimming speed and phylogenetic relationships. Recent work in several laboratories has been directed at studying patterns of muscle power output in vitro under simulated swimming conditions. This work suggests that the way that fish generate muscle power and convert it into thrust through the body and caudal fin does indeed vary. However, despite the differences, several features appear to be common to virtually all species studied and suggest where future effort should be directed if muscle function in swimming fish is to be better understood.