Labriform Swimmers Research Articles

Design of a Labriform-Steering Underwater Robot Using a Multiphysics Simulation Environment

Bio-inspired solutions devised for Autonomous Underwater Robots are currently investigated by researchers as a source of propulsive improvement. To address this ambitious objective, the authors have designed a carangiform swimming robot, which represents a compromise in terms of efficiency and maximum velocity. The requirements of stabilizing a course and performing turns were not met in their previous works. Therefore, the aim of this paper is to improve the vehicle maneuvering capabilities by means of a novel transmission system capable of transforming the constant angular velocity of a single rotary actuator into the pitching–yawing rotation of fish pectoral fins. Here, the biomimetic thrusters exploit the drag-based momentum transfer mechanism of labriform swimmers to generate the necessary steering torque. Aside from inertia and encumbrance reduction, the main improvement of this solution is the inherent synchronization of the system granted by the mechanism’s kinematics. The system was sized by using the experimental results collected by biologists and then integrated in a multiphysics simulation environment to predict the resulting maneuvering performance.

A simplified computational model of possible hydrodynamic interactions between respiratory and swimming-related water flows in labriform-swimming fishes

Hydrodynamic interactions in bony fishes between respiratory fluid flows leaving the opercular openings and simultaneous flows generated by movements of downstream pectoral fins are both poorly understood and likely to be complex. Labriform-swimming fishes that swim primarily by moving only their pectoral fins are good subjects for these studies. We performed a computational fluid dynamics investigation of a simplified 2D model of these interactions based on previously published experimental observations of both respiratory and pectoral fin movements under both resting and slow, steady swimming conditions in two similar labriform swimmers: the bluegill sunfish (L. macrochirus) and the largemouth bass (M. salmoides). We carried out a parametric study investigating the effects that swimming speed, strength of opercular flow and phase difference between the pectoral fin motion and the opercular opening and closing have on the thrust and sideslip forces generated by the pectoral fins during both the abduction and adduction portions of the fin movement cycle. We analyzed pressure distributions on the fin surface to determine physical differences in flows with and without opercular jets. The modeling indicates that complex flow structures emerge from the coupling between the opercular jets and vortex shedding from pectoral fins. The jets from the opercular openings appear to exert significant influence on the forces generated by the fins; they are potentially significant in the maneuverability of at least some labriform swimmers. The numerical simulations and the analysis establish a framework for the study of these interactions in various labriform swimmers in a variety of flow regimes. Similar situations in groups of fishes using other swimming modes should also be investigated.

Turbulent flow reduces oxygen consumption in the labriform swimming shiner perch, Cymatogaster aggregata.

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, Cymatogaster aggregata (a labriform swimmer), were affected by turbulence, two flow conditions were constructed in a swim-tunnel respirometer. A low-turbulence flow was created using a common swim-tunnel respirometry setup with a flow straightener and fine-mesh grid to minimize velocity fluctuations. A high-turbulence flow condition was created by allowing large velocity fluctuations to persist without a flow straightener or fine grid. The two conditions were tested with particle image velocimetry to confirm significantly different turbulence properties throughout a range of mean flow speeds. Oxygen consumption rate of the swimming fish increased with swimming speed and pectoral fin beat frequency in both flow conditions. Higher turbulence also caused a greater positional variability in swimming individuals (versus low-turbulence flow) at medium and high speeds. Surprisingly, fish used less oxygen in high-turbulence compared with low-turbulence flow at medium and high swimming speeds. Simultaneous measurements of swimming kinematics indicated that these reductions in oxygen consumption could not be explained by specific known flow-adaptive behaviours such as Kármán gaiting or entraining. Therefore, fish in high-turbulence flow may take advantage of the high variability in turbulent energy through time. These results suggest that swimming behaviour and energetics measured in the lab in straightened flow, typical of standard swimming respirometers, might differ from that of more turbulent, semi-natural flow conditions.

Intraspecific variation in aerobic and anaerobic locomotion: gilthead sea bream (Sparus aurata) and Trinidadian guppy (Poecilia reticulata) do not exhibit a trade-off between maximum sustained swimming speed and minimum cost of transport.

Intraspecific variation and trade-off in aerobic and anaerobic traits remain poorly understood in aquatic locomotion. Using gilthead sea bream (Sparus aurata) and Trinidadian guppy (Poecilia reticulata), both axial swimmers, this study tested four hypotheses: (1) gait transition from steady to unsteady (i.e., burst-assisted) swimming is associated with anaerobic metabolism evidenced as excess post exercise oxygen consumption (EPOC); (2) variation in swimming performance (critical swimming speed; Ucrit) correlates with metabolic scope (MS) or anaerobic capacity (i.e., maximum EPOC); (3) there is a trade-off between maximum sustained swimming speed (Usus) and minimum cost of transport (COTmin); and (4) variation in Usus correlates positively with optimum swimming speed (Uopt; i.e., the speed that minimizes energy expenditure per unit of distance traveled). Data collection involved swimming respirometry and video analysis. Results showed that anaerobic swimming costs (i.e., EPOC) increase linearly with the number of bursts in S. aurata, with each burst corresponding to 0.53 mg O2 kg−1. Data are consistent with a previous study on striped surfperch (Embiotoca lateralis), a labriform swimmer, suggesting that the metabolic cost of burst swimming is similar across various types of locomotion. There was no correlation between Ucrit and MS or anaerobic capacity in S. aurata indicating that other factors, including morphological or biomechanical traits, influenced Ucrit. We found no evidence of a trade-off between Usus and COTmin. In fact, data revealed significant negative correlations between Usus and COTmin, suggesting that individuals with high Usus also exhibit low COTmin. Finally, there were positive correlations between Usus and Uopt. Our study demonstrates the energetic importance of anaerobic metabolism during unsteady swimming, and provides intraspecific evidence that superior maximum sustained swimming speed is associated with superior swimming economy and optimum speed.

The morphological basis of labriform rowing in the deep-sea Bigscale Scopelogadus beanii (Percomorpha: Beryciformes)

A recent shipboard video reveals that the deep-sea melamphaeid fish Scopelogadus beanii is capable of rowing labriform propulsion. These data indicate that S. beanii engages in powerful and highly maneuverable drag-based locomotion, an energetically expensive swimming mode in which the pectoral fin produces thrust from a fore-aft rowing stroke. The pectoral-girdle musculoskeletal morphology, including muscle insertions and origins is described herein, and estimations of isometric force produced by each division are reported based on calculations of physiological cross-sectional area. The study species possesses similar adductor muscle configuration but has one fewer abductor muscle as compared to previously studied rowers. In addition, girdle muscle masses are compared with a previously published morphospace of labriform swimmers. From this analysis, it is inferred that muscles occupying a portion of morphospace not yet described for rowing fishes, power the dynamic sculling of S. beanii. Placing these results in an ecomorphological context, the resource utilization of S. beanii is considered, specifically that it is a consumer of gelatinous zooplankton, a consistently distributed food resource. Although S. beanii resides in the dimensionless bathypelagic zone of the open ocean, a swimming mode that increases maneuverability is perhaps an adaptation to feed among dense aggregations of its prey.

Unsteady flow affects swimming energetics in a labriform fish (Cymatogaster aggregata)

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, during station holding. Using intermittent-flow respirometry, we measured critical swimming speed (Ucrit), oxygen consumption rates (O2) and pectoral fin use in steady flow versus unsteady flows with either low- [0.5 body lengths (BL) s(-1)] or high-amplitude (1.0 BL s(-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.

How to build a pectoral fin: functional morphology and steady swimming kinematics of the spotted ratfish (Hydrolagus colliei)

Aquatic flight is the primary locomotor mode for many animals, including penguins and other diving birds, turtles, and fishes, where labriform and rajiform swimming have been the focus of much interest. However, despite its interesting phylogenetic placement, little is known about the aquatic flight of the sister lineage to the elasmobranchs, the chimaerids. This study investigates the pectoral fin morphology of the spotted ratfish ( Hydrolagus colliei (Lay and Bennett, 1839)) as a possible factor underlying the kinematics of their steady swimming by comparing muscle mass, distribution, and abductor to adductor ratio with those of a closely related shark ( Squalus acanthias L., 1758). Despite fundamental differences in swimming mode, abductor to adductor muscle ratio did not differ between species (P = 0.49). However, the muscle ratio in the spotted ratfish was similar to the range determined in other flapping labriform swimmers. Ratfish had larger, distally placed pectoral fin muscles relative to body size than dogfish (P < 0.0001) possibly aiding in fine control. Stroke amplitude remained constant across body size (P = 0.26) and relative swimming speed (P = 0.23) in the ratfish, whereas the downstroke was significantly faster than the upstroke (P = 0.006). The similar muscle ratio, despite differences in stroke phases, may be explained by physiological or in vivo recruitment differences between abductors and adductors in the ratfish.

Partition of aerobic and anaerobic swimming costs related to gait transitions in a labriform swimmer

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.

Gait transition and oxygen consumption in swimming striped surfperch Embiotoca lateralis Agassiz

A flow‐through respirometer and swim tunnel was used to estimate the gait transition speed (Up‐c) of striped surfperch Embiotoca lateralis, a labriform swimmer, and to investigate metabolic costs associated with gait transition. The Up‐c was defined as the lowest speed at which fish decrease the use of pectoral fins significantly. While the tail was first recruited for manoeuvring at relatively low swimming speeds, the use of the tail at these low speeds [as low as 0·75 body (fork) lengths s−1, LF s−1) was rare (<10% of the total time). Tail movements at these low speeds appeared to be associated with occasional slow manoeuvres rather than providing power. As speed was increased beyond Up‐c, pectoral fin (PF) frequencies kept increasing when the tail was not used, while they did not when PF locomotion was aided by the tail. At these high speeds, the tail was employed for 40–50% of the time, either in addition to pectoral fins or during burst‐and‐coast mode. Oxygen consumption increased exponentially with swimming speeds up to gait transition, and then levelled off. Similarly, cost of transport (CT) decreased with increasing speed, and then levelled off near Up‐c. When speeds ≥Up‐c are considered, CT is higher than the theoretical curve extrapolated for PF swimming, suggesting that PF swimming appears to be higher energetically less costly than undulatory swimming using the tail.

Mode of locomotion places selective pressures on Antarctic and temperate labriform swimming fish

The physiological responses to exercise and stress of the Antarctic labriform swimmer Pagothenia borchgrevinki were compared to the temperate labriform swimmers Notolabrus celidotus and Notolabrus fucicola. Basic swimming characteristics were very similar amongst the three species with P. borchgrevinki showing a reduced capacity for exercise. P. borchgrevinki showed large increases in haematocrit (Hct) following exercise that were not seen in the temperate species. Lactate dehydrogenase (LDH) activities were high in the white myotomal muscle from the Antarctic fish, with a distinct indication of metabolic cold adaptation in this enzyme. Nevertheless, although the temperate fish showed elevated muscle lactate concentrations following either exercise or electrical stimulation the Antarctic fish did not. The data suggest that poor anaerobic performance of white muscle is associated with the labriform mode of locomotion.

Gait transition speed, pectoral fin‐beat frequency and amplitude in Cymatogaster aggregata, Embiotoca lateralis and Damalichthys vacca

Surfperches are labriform swimmers and swim primarily with their pectoral fins, using the tail to assist only at higher speeds. The transition, from pectoral to pectoral and caudal fins, occurs at a threshold speed that has been termed physiologically and biomechanically ‘equivalent’ for fishes of different size. The gait transition (UP‐C) of Cymatogaster aggregata occurred at a higher speed (measured in bodylengths s−1) for smaller fish than larger fish. At UP‐C, pectoral fin‐beat frequency was size‐dependent: smaller fish have a higher pectoral fin‐beat frequency than larger fish. In contrast, at low speeds (i.e. <60% of UP‐C) the pectoral fin‐beat frequency was independent of the size of the fish. Inter‐specific comparisons of UP‐C, pectoral fin‐beat frequency and amplitude among C. aggregata, Embiotoca lateralis and Damalichthys vacca showed that C. aggregata had a higher UP‐C than E. lateralis and D. vacca. The pectoral fin‐beat frequency at UP‐C showed no significant differences among species. Cymatogaster aggregata achieved higher UP‐C, in part, through increased fin beat amplitude rather than frequency. These differences in performance may be related to the different habitats in which these species live.

Labriform propulsion in fishes: kinematics of flapping aquatic flight in the bird wrasse Gomphosus varius (Labridae)

Labriform, or pectoral fin, propulsion is the primary swimming mode for many fishes, even at high relative speeds. Although kinematic data are critical for evaluating hydrodynamic models of propulsion, these data are largely lacking for labriform swimmers, especially for species that employ an exclusively labriform mode across a broad range of speeds. We present data on pectoral fin locomotion in Gomphosus varius (Labridae), a tropical coral reef fish that uses a lift-based mechanism to fly under water at sustained speeds of 1­6 total body lengths s-1 (TL s-1). Lateral- and dorsal-view video images of three fish swimming in a flow tank at 1­4 TL s-1 were recorded at 60 Hz. From the two views, we reconstructed the three-dimensional motion of the center of mass, the fin tip and two fin chords for multiple fin beats of each fish at each of four speeds. In G. varius, the fin oscillates largely up and down: the stroke plane is tilted by approximately 20 ° from the vertical. Both frequency and the area swept by the pectoral fins increase with swimming speed. Interestingly, there are individual differences in how this area increases. Relative to the fish, the fin tip in lateral view moves along the path of a thin, inclined figure-of-eight. Relative to a stationary observer, the fin tip traces a sawtooth pattern, but the teeth are recumbent (indicating net backwards movement) only at the slowest speeds. Distal fin chords pitch nose downward during the downstroke and nose upward during the upstroke. Hydrodynamic angles of attack are largely positive during the downstroke and negative during the upstroke. The geometry of the fin and incident flow suggests that the fin is generating lift with large upward and small forward components during the downstroke. The negative incident angles during the upstroke suggest that the fin is generating largely thrust during the upstroke. In general, the large thrust is combined with a downward force during the upstroke, but the net backwards motion of the fin at slow speeds generates a small upward component during slow swimming. Both the alternating sign of the hydrodynamic angle of attack and the observed reduced frequencies suggest that unsteady effects are important in G. varius aquatic flight, especially at low speeds. This study provides a framework for the comparison of aquatic flight by fishes with aerial flight by birds, bats and insects.

Effect of stimulus train duration and cycle frequency on the capacity to do work in the pectoral fin muscle of the pumpkinseed sunfish, Lepomis gibbosus

The goal of our experiment was to elucidate the effect of stimulus duty cycle (the percentage of the cycle that the muscle was stimulated), phase (the relative timing of the imposed sinusoidal length change and stimulation), and muscle cycle frequency (the speed at which the muscle was cycled) on work and power in the pectoral fin muscle of a labriform swimmer, the pumpkinseed sunfish, Lepomis gibbosus. Stimulus train duration was varied from a twitch to a 40% duty cycle; cycle frequency was varied from 1 to 8 Hz. Work was calculated as the area of work loops produced by muscle contractions while the muscle was undergoing sinusoidal length changes. Maximum net work per cycle (6.2 J/kg) was produced at 1 Hz cycle frequency and a 32% duty cycle. Maximum power (26.7 W/kg) was produced at 5 Hz cycle frequency and a 16% duty cycle. As cycle frequency increased, the duty cycle and the stimulus train duration that produced maximum work decreased. The relatively long relaxation time compared with the length of time required to complete the whole cycle precluded the muscle from doing net positive work at high cycle frequencies.

Energetics of swimming in fishes using different methods of locomotion: I. Labriform swimmers

The patterns relating rates of oxygen consumption to steady sustained and prolonged swimming at different speeds were determined in adults or near adults of two species of marine fishes that use the labriform mode of swimming (labriform swimmers). Effects of acute temperature changes on these patterns were measured. Species were the shiner surfperch,Cymatogaster aggregata and the señorita wrasse,Oxyjulis californica.Metabolic data were analyzed three different ways. The first (method of Brett) was based upon mass specific oxygen uptake and length specific swim speed; data in this form were analyzed both as best-fit power functions and as the mathematically equivalent least squares linear regressions for semi-log plots. The second and third methods were based upon drag based hydromechanical theory concerning power requirements for swimming in fishes: total metabolic ratesvs. absolute swimming speeds, analyzed both as best-fit power functions and least squares linear regressions for log-log plots.The main finding, demonstrated by all three methods of calculation, was that the slopes of all regression lines (both semi-log and log-log) and the exponents of almost all power functions (five out of six) were very low. The Brett method applied to subcarangiform swimmers usually produces slopes averaging 0.36 (using base-10 logarithms). The slopes calculated by that method in the present study were 0.02-0.08. Low slope values could result from the interactions of many factors. Additional data are needed to determine which combinations of factors actually produced them. On this basis metabolic rate data on intact labriform swimmers, by themselves, appear unusable as empirical tests of theory based predictions concerning power requirements for fish swimming.

Pectoral Fin Morphology: a Simple Relation With Movement Pattern?

Adaptation of form to function of the pectoral fin is usually straightforward and clear in teleost fishes when the fins are used for special purposes. Adaptations are not obvious when species are compared which predominantly use the pectorals either for manoeuvring or for labriform swimming. Two explanations are possible: 1. The differences in movement patterns between manoeuvring and labriform swimmers originate entirely from a cybernetic level and the fin morphology can therefore be identical. 2. The different functions are related to small morphological differences which thus far have been overlooked. To test this, the pectoral fin morphology of a manoeuvring species, Sarotherodon niloticus (Cichlidae) and of two species showing labriform swimming, Coris formosa and C. julis (Labridae), are compared in detail. The morphological differences between the two Coris species are smaller than the differences between S. niloticus and the two Coris species. It is concluded that the pectoral fin morphology of these three species differs in small details, part of which can be related to differences in fin movement patterns. The cybernetic origin of these differences predominates, supported by only minute morphological adaptations.