A Three-Dimensional Kinematics Analysis of a Koi Carp Pectoral Fin by Digital Image Processing

Pectoral fins fascinate researchers for their important role in fish maneuvers. By possessing a complicated flexible structure with several fin rays made by a thin film, the fin exhibits a three-dimensional (3D) motion. The complex 3D fin kinematics makes it challenging to study the performance of pectoral fin. Nevertheless, a detailed study on the 3D motion pattern of pectoral fins is necessary to the design and control of a bio-inspired fin rays. Therefore, a highspeed photography system is introduced in this paper to study the 3D motion of a Koi Carp by analyzing the two views of its pectoral fin simultaneously. The key motions of the pectoral fins are first captured in both hovering and retreating. Next, the 3D configuration of the pectoral fins is reconstructed by digital image processing, in which the movement of fin rays during fish retreating and hovering is obtained. Furthermore, the method of Singular Value Decomposition (SVD) is adopted to extract the basic motion patterns of pectoral fins from extensive image sequences, i.e. expansion, bending, cupping, and undulation. It is believed that the movement of the fin rays and the basic patterns of the pectoral fins obtained in the present work can provide a good foundation for the development and control of bionic flexible pectoral fins for underwater propeller.     

Maneuvering hydrodynamics of fish and small underwater vehicles

The understanding of fish maneuvering and its application tounderwater rigid bodies are considered. The goal is to gaininsight into stealth. The recent progress made in NUWC is reviewed.Fish morphology suggests that control fins for maneuverabilityhave unique scalar relationships irrespective of their speedtype. Maneuvering experiments are carried out with fish thatare fast yet maneuverable. The gap in maneuverability betweenfish and small underwater vehicles is quantified. The hydrodynamicsof a dorsal fin based brisk maneuvering device and a dual flappingfoil device, as applied to rigid cylindrical bodies, are described.The role of pectoral wings in maneuvering and station keepingnear surface waves is discussed. A pendulum model of dolphinswimming is presented to show that body length and tail flappingfrequency are related. For nearly neutrally buoyant bodies,Froude number and maneuverability are related. Analysis of measurementsindicates that the Strouhal number of dolphins is a constant.The mechanism of discrete and deterministic vortex sheddingfrom oscillating control surfaces has the property of largeamplitude unsteady forcing and an exquisite phase dependence,which makes it inherently amenable to active control for precisionmaneuvering. Theoretical control studies are carried out todemonstrate the feasibility of maneuverability of biologicallyinspired bodies under surface waves. The application of fishhydrodynamics to the silencing of propulsors is considered.Two strategies for the reduction of radiated noise are developed.The effects of a reduction of rotational rate are modeled. Theactive cambering of blades made of digitally programmable artificialmuscles, and their thrust enhancement, are demonstrated. Next,wake momentum filling is carried out by artificial muscles atthe trailing edge of a stator blade of an upstream stator propulsor,and articulating them like a fish tail. A reduction of radiatednoise, called blade tonals, is demonstrated theoretically.     

Establishment of a biomimetic device based on tri-layer polymer actuators--propulsion fins

We propose to use bending type tri-layer polymer actuators as propulsion fins for a biomimetic device consisting of a rigid body, like a box fish having a carapace, and paired fins running through the rigid body, like a fish having pectoral fins. The fins or polymer bending actuators can be considered as individually controlled flexible membranes. Each fin is activated with sinusoidal inputs such that there is a phase lag between the movements of successive fins to create enough thrust force for propulsion. Eight fins with 0.125 aspect ratio have been used along both sides of the rigid body to move the device in the direction perpendicular to the longitudinal axis of the body. The designed device with the paired fins was successfully tested, moving in an organic solution consisting of solvent, propylene carbonate (PC), and electrolyte. The design procedure outlined in this study is offered as a guide to making functional devices based on polymer actuators and sensors.     

Ecomorphology of Locomotion in Labrid Fishes

The Labridae is an ecologically diverse group of mostly reef associated marine fishes that swim primarily by oscillating their pectoral fins. To generate locomotor thrust, labrids employ the paired pectoral fins in motions that range from a fore-aft rowing stroke to a dorso-ventral flapping stroke. Species that emphasize one or the other behavior are expected to benefit from alternative fin shapes that maximize performance of their primary swimming behavior. We document the diversity of pectoral fin shape in 143 species of labrids from the Great Barrier Reef and the Caribbean. Pectoral fin aspect ratio ranged among species from 1.12 to 4.48 and showed a distribution with two peaks at about 2.0 and 3.0. Higher aspect ratio fins typically had a relatively long leading edge and were narrower distally. Body mass only explained 3% of the variation in fin aspect ratio in spite of four orders of magnitude range and an expectation that the advantages of high aspect ratio fins and flapping motion are greatest at large body sizes. Aspect ratio was correlated with the angle of attachment of the fin on the body (r = 0.65), indicating that the orientation of the pectoral girdle is rotated in high aspect ratio species to enable them to move their fin in a flapping motion. Field measures of routine swimming speed were made in 43 species from the Great Barrier Reef. Multiple regression revealed that fin aspect ratio explained 52% of the variation in size-corrected swimming speed, but the angle of attachment of the pectoral fin only explained an additional 2%. Labrid locomotor diversity appears to be related to a trade-off between efficiency of fast swimming and maneuverability in slow swimming species. Slow swimmers typically swim closer to the reef while fast swimmers dominate the water column and shallow, high-flow habitats. Planktivory was the most common trophic associate with high aspect ratio fins and fast swimming, apparently evolving six times.     

Does body and fin form affect the maneuverability of fish traversing vertical and horizontal slits?

Synopsis The purpose of this study was to determine if body and fin form affected the maneuverability of teleostean fishes as measured by their ability to negotiate simple obstacles. Obstacles were vertical and horizontal rectangular slits of different widths, for which width was defined as the minimum dimension of a slit irrespective of slit orientation. Performance was measured as the smallest slit width traversed. Three species with different body and fin patterns were induced to swim through slits. Species tested were; goldfish Carassius auratus with a fusiform body, anterio-ventral pectoral fins and posterio-ventral pelvic fins; silver dollars Metynnis hypsauchen with the same fin configurations but a gibbose body; angelfish Pterophyllum scalare with a gibbose body and anterio-lateral pectoral fins. Minimum slit widths negotiated were normalized with the length of various body dimensions: total length, maximum width, span at the pectoral fins, and volume^1/3 (numerically equal to mass^1/3). Goldfish had the poorest performance, requiring the largest slit widths relative to these body dimensions. No consistent patterns in performance were found for silver dollars vs. angelfish. There were no differences among species in the ratio of minimum vertical slit width negotiated to that for horizontal slits, indicating fish were equally able to control posture while swimming on their sides. There were also no consistent patterns in the times taken to transit slits. Although the deep-bodied fish were able to maneuver through smaller slits, the most striking result is the similarity of minimum slit widths traversed in spite of the large variation in body form. Body form and fin plan may be more important for maneuvering and posture control during sub-maximum routine activities.     

对胸鳍棘鉴定鱼类年龄方法的技术改进——简易脱钙切片法

用大鳍Hu、粗唇Wei、瓦氏黄颡鱼等的胸鳍棘作为实验材料,用1％－5％的硝酸脱钙切片后,鉴定年龄。为适应大规模的年龄鉴定,对常规的组织切片步骤和时间进行了简化、缩短。与传统的锯片法及磨片法相比,该方法易于操作,有助于准确的年龄鉴定、年轮半径测量和生长推算,特别适用于中、小型无鳞鱼类的年龄鉴定。     

Synchronized swimming: coordination of pelvic and pectoral fins during augmented punting by the freshwater stingray Potamotrygon orbignyi

Benthic animals live at the juncture of fluid and solid environments, an interface that shapes many aspects of their behavior, including their means of locomotion. Aquatic walking and similar substrate-dependent forms of underwater propulsion have evolved multiple times in benthic invertebrate and vertebrate taxa, including batoid elasmobranchs. Skates (Rajidae) use the pelvic fins to punt across the substrate, keeping the pectoral fin disc still. Other batoids combine pelvic fin motions with pectoral fin undulation in augmented punting, but the coordination of these two modes has not been described. In this study of an augmented punter, the freshwater stingray Potamotrygon orbignyi, we demonstrate the synchrony of pelvic and pectoral fin cycles. The punt begins as the pelvic fins, held in an anterior position, are planted into the substrate and used to push the body forward. Meanwhile, a wave of pectoral fin undulation begins, increasing to maximum height just before the cycle's halfway point, when the pelvic fins reach their furthest posterior extension. The pectoral fin wave subsides as the pelvic fins return to their starting position for subsequent punts. Despite definitive links between pectoral and pelvic fin activity, we find no significant relationship between pectoral fin kinematics (frequency, wave height, and wave speed) and punt performance. However, slip calculations indicate that pectoral undulation can produce thrust and augment punting. Pelvic fin kinematics (frequency and duty factor) have significant effects, suggesting that while both sets of fins contribute to thrust generation, the pelvic fins likely determine punt performance.     

Microanatomy of the paired‐fin pads of ostariophysan fishes (Teleostei: Ostariophysi)

Members of the teleost superorder Ostariophysi dominate freshwater habitats on all continents except Antarctica and Australia. Obligate benthic and rheophilic taxa from four different orders of the Ostariophysi (Gonorynchiformes, Cypriniformes, Characiformes, and Siluriformes) frequently exhibit thickened pads of skin along the ventral surface of the anteriormost ray or rays of horizontally orientated paired (pectoral and pelvic) fins. Such paired‐fin pads, though convergent, are externally homogenous across ostariophysan groups (particularly nonsiluriform taxa) and have been considered previously to be the result of epidermal modification. Histological examination of the pectoral and/or pelvic fins of 44 species of ostariophysans (including members of the Gonorynchiforms, Cypriniformes, Characiformes, and Siluriformes) revealed a tremendous and previously unrecognized diversity in the cellular arrangement of the skin layers (epidermis and subdermis) contributing to the paired‐fin pads. Three types of paired‐fin pads (Types 1–3) are identified in nonsiluriform ostariophysan fishes, based on differences in the cellular arrangement of the epidermis and subdermis. The paired‐fin pads of siluriforms may or may not exhibit a deep series of ridges and grooves across the surface. Two distinct patterns of unculus producing cells are identified in the epidermis of the paired‐fin pads of siluriforms, one of which is characterized by distinct bands of keratinization throughout the epidermis and is described in Amphilius platychir (Amphiliidae) for the first time. General histological comparisons between the paired fins of benthic and rheophilic ostariophysan and nonostariophysan percomorph fishes are provided, and the possible function(s) of the paired‐fin pads of ostariophysan fish are discussed. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.     

The evolution of paired fins

Summary The Archipterygium is Gegenbaur’s most lasting contribution to the study of vertebrate limb evolution. This transformational hypothesis of gill arches to limb girdles, rays to fins, and proposal of a vertebrate fin-limb groundplan, is generally treated as a flawed alternative to the more widely accepted lateral fin-fold hypothesis of vertebrate limb evolution. When compared to the phylogenetic distribution and diversity of fins and limbs, both hypotheses fail. Dermal skeletal lateral folds, spines and keels originate repeatedly in vertebrate evolution, but paired fins with girdles originate at pectoral level and are anteroposteriorly restricted. Pelvic fins emerge later in phylogeny; pectoral and pelvic appendages primitively differ. Endoskeletal girdles never exhibit characteristics of gill arches. The emergent sequence of paired fin evolution depends upon phylogenetic hypotheses within which extant agnathan interrelationships are uncertain; positions of jawless fossil fish along the gnathostome stem are insecure; the fossil data set is patchy. However, certain features of the data set are robust. This has prompted a reconsideration of Gegenbaur’s hypothesized arch-girdle relationship, and an iterative homology between scapulocoracoid and extrabranchial cartilages is suggested. No transformation of arch to girdle is necessarily implied, but some signal of developmental relatedness is predicted.     

Fish and chips: implementation of a neural network model into computer chips to maximize swimming efficiency in autonomous underwater vehicles

Recent developments in the design and propulsion of biomimetic autonomous underwater vehicles (AUVs) have focused on boxfish as models (e.g. Deng and Avadhanula 2005 Biomimetic micro underwater vehicle with oscillating fin propulsion: system design and force measurement Proc. 2005 IEEE Int. Conf. Robot. Auto. (Barcelona, Spain) pp 3312-7). Whilst such vehicles have many potential advantages in operating in complex environments (e.g. high manoeuvrability and stability), limited battery life and payload capacity are likely functional disadvantages. Boxfish employ undulatory median and paired fins during routine swimming which are characterized by high hydromechanical Froude efficiencies (approximately 0.9) at low forward speeds. Current boxfish-inspired vehicles are propelled by a low aspect ratio, 'plate-like' caudal fin (ostraciiform tail) which can be shown to operate at a relatively low maximum Froude efficiency (approximately 0.5) and is mainly employed as a rudder for steering and in rapid swimming bouts (e.g. escape responses). Given this and the fact that bioinspired engineering designs are not obligated to wholly duplicate a biological model, computer chips were developed using a multilayer perception neural network model of undulatory fin propulsion in the knifefish Xenomystus nigri that would potentially allow an AUV to achieve high optimum values of propulsive efficiency at any given forward velocity, giving a minimum energy drain on the battery. We envisage that externally monitored information on flow velocity (sensory system) would be conveyed to the chips residing in the vehicle's control unit, which in turn would signal the locomotor unit to adopt kinematics (e.g. fin frequency, amplitude) associated with optimal propulsion efficiency. Power savings could protract vehicle operational life and/or provide more power to other functions (e.g. communications).     

Functional morphology of the pectoral fins in bamboo sharks, Chiloscyllium plagiosum: benthic vs. pelagic station-holding

Bamboo sharks (Chiloscyllium plagiosum) are primarily benthic and use their relatively flexible pectoral and pelvic fins to rest on and move about the substrate. We examined the morphology of the pectoral fins and investigated their locomotory function to determine if pectoral fin function during both benthic station-holding and pelagic swimming differs from fin function described previously in leopard sharks, Triakis semifasciata. We used three-dimensional kinematics and digital particle image velocimetry (DPIV) to quantify pectoral fin function in five white-spotted bamboo sharks, C. plagiosum, during four behaviors: holding station on the substrate, steady horizontal swimming, and rising and sinking during swimming. During benthic station-holding in current flow, bamboo sharks decrease body angle and adjust pectoral fin angle to shed a clockwise fluid vortex. This vortex generates negative lift more than eight times that produced during open water vertical maneuvering and also results in an upstream flow that pushes against the posterior surface of the pectoral fin to oppose drag. In contrast, there is no evidence of significant lift force in the wake of the pectoral fin during steady horizontal swimming. The pectoral fin is held concave downward and at a negative dihedral angle during steady horizontal swimming, promoting maneuverability rather than stability, although this negative dihedral angle is much less than that observed previously in sturgeon and leopard sharks. During sinking, the pectoral fins are held concave upward and shed a clockwise vortex with a negative lift force, while in rising the pectoral fin is held concave downward and sheds a counterclockwise vortex with a positive lift force. Bamboo sharks appear to sacrifice maneuverability for stability when locomoting in the water column and use their relatively flexible fins to generate strong negative lift forces when holding position on the substrate and to enhance stability when swimming in the water column.     

Numerical and Experimental Research on Modular Oscillating Fin

Fishes are famous for their ability to position themselves accurately even in turbulent flows. This ability is the result of the coordinated movement of fins which extend from the body. We have embarked on a research program designed to develop an agile and high efficient biologically inspired robotic fish based on the performance of hybrid mechanical fms. To accomplish this goal, a mechanical ray-like fin actuated by Shape Memory Alloy （SMA） is developed, which can realize both oscillatory locomotion and undulatory locomotion. We first give a brief introduction on the mechanical structure of our fin and then carry out theoretic analysis on force generation. Detailed information of these theoretical results is later revealed by Computational Huid Dynamic （CFD）, and is final validated by experiments. This robotic fin has potential application as a propulsor for future underwater vehicles in addition to being a valuable scientific instrument.     

Single rays as indicators of fin vestigialization in coho salmon: patterns and perspectives

Although finrays in salmon normally contain a pair of elements (biramous), finrays with a single element (uniramous) occasionally develop. Exposure to chronic stress during character development has been shown to increase fluctuating asymmetry, suggesting the occurrence of single finrays may be stress‐induced. On the other hand, single finrays may be evolutionary atavisms, reflecting fin vestigialization caused by reduced selection pressure. To assess the merits of these hypotheses, cleared and stained paired and median fins were examined for single finrays in juvenile coho salmon (Oncorhynchus kisutch Walbaum) from two compatible hatchery stocks and their reciprocal hybrids which had been exposed to different patterns of chronic temperature fluctuation throughout embryogenesis. In the median fins, uniramous secondary finrays predominated, and single primary finrays were infrequent. Single finrays in the median fins did not respond to thermal treatment or cross, suggesting the fins were evolutionarily stable and under strong developmental control. The paired fins were observed to contain only primary finrays. Frequencies of single pelvic finrays increased under thermal stress, as did fluctuating asymmetry, suggesting increased sensitivity to stress due to reduced developmental control in this fin. However, the presence or absence of single finrays in the paired fins did not alter the statistical significance of the conclusions regarding levels of fluctuating asymmetry, the number of asymmetric fish, or the contribution to meristic variation from asymmetry. Locations of single finrays in the paired fins were unaffected by thermal treatment or cross. Single finrays were most commonly observed in the trailing margins of both paired fins, a finding consistent with vestigialization theory. Frequency histograms of single pectoral finray locations revealed a second peak in the leading quarter of the fin. The esults support the hypothesis that single primary finrays are evolutionary atavisms, and that reduced selection pressure is differentially influencing the paired fins.     

The morphology of the cephalic lobes and anterior pectoral fins in six species of batoids

Many benthic batoids utilize their pectoral fins for both undulatory locomotion and feeding. Certain derived, pelagic species of batoids possess cephalic lobes, which evolved from the anterior pectoral fins. These species utilize the pectoral fins for oscillatory locomotion while the cephalic lobes are used for feeding. The goal of this article was to compare the morphology of the cephalic lobes and anterior pectoral fins in species that possess and lack cephalic lobes. The skeletal elements (radials) of the cephalic lobes more closely resembled the radials in the pectoral fin of undulatory species. Second moment of area (I), calculated from cephalic lobe radial cross sections, and the number of joints revealed greater flexibility and resistance to bending in multiple directions as compared to pectoral fin radials of oscillatory species. The cephalic lobe musculature was more complex than the anterior pectoral fin musculature, with an additional muscle on the dorsal side, with fiber angles running obliquely to the radials. In Rhinoptera bonasus, a muscle presumably used to help elevate the cephalic lobes is described. Electrosensory pores were found on the cephalic lobes (except Mobula japonica) and anterior pectoral fins of undulatory swimmers, but absent from the anterior pectoral fins of oscillatory swimmers. Pore distributions were fairly uniform except in R. bonasus, which had higher pore numbers at the edges of the cephalic lobes. Overall, the cephalic lobes are unique in their anatomy but are more similar to the anterior pectoral fins of undulatory swimmers, having more flexibility and maneuverability compared to pectoral fins of oscillatory swimmers. The maneuverable cephalic lobes taking on the role of feeding may have allowed the switch to oscillatory locomotion and hence, a more pelagic lifestyle. J. Morphol. 274:1070–1083, 2013. © 2013 Wiley Periodicals, Inc.     

Wing design and scaling of flying fish with regard to flight performance

Fin and body dimensions of six genera of flying fish (Exocoetidae) were examined to study variation in morphological parameters in relation to aerodynamics performance. The fins are modified as wings for gliding flight. Fin area and fin span increase with increasing body mass, whereas the percentage of wing area contributed by the pectoral fins and the percentage of the caudal fin area contributed by the hypocaudal lobe remain constant. The aerodynamic design of flying fish approximates the monoplane-biplane classification proposed by Breder (1930). Scaling relationships for wing loading and aspect ratio indicate that wing morphology in the Exocoetidae is more similar to birds and bats than to other gliders. The flight performance of flying fish is a high-speed glide with a relatively flat trajectory. The wing, as indicated by the aspect ratio, is designed for high lift with low drag characteristics.     

Wake dynamics and locomotor function in fishes: interpreting evolutionary patterns in pectoral fin design

The great anatomical diversification of paired fins within theActinopterygii (ray-finned fishes) can be understood as a suiteof evolutionary transformations in design. At a broad taxonomicscale, two clear trends exist in the morphology of the anteriorlysituated pectoral fins. In comparing basal to more derived clades,there are general patterns of (i) reorientation of the pectoralfin base from a nearly horizontal to more vertical inclination,and (ii) migration of the pectoral fin from a ventral to mid-dorsalbody position. As yet, the functional significance of thesehistorical trends in pectoral fin design remains largely untestedby experiment. In this paper we test the proposal that variationin pectoral fin structure has an important influence on themagnitude and orientation of fluid forces generated during maneuveringlocomotion. Using digital particle image velocimetry for quantitativewake visualization, we measure swimming forces in ray-finnedfishes exhibiting the plesiomorphic and apomorphic pectoralfin anatomy. Our experiments focus on rainbow trout (Oncorhynchusmykiss), a lower teleost with pectoral fins positioned ventrallyand with nearly horizontally inclined fin bases, and bluegillsunfish (Lepomis macrochirus), a relatively derived perciformfish with more vertically oriented pectoral fins positionedmid-dorsally on the body. In support of hypotheses arising fromour prior wake studies and previously untested models in theliterature, we find that the pectoral fins of sunfish generatesignificantly higher forces for turning and direct braking forcescloser to the center of mass of the body than the pectoral finsof trout. These results provide insight into the hydrodynamicimportance of major evolutionary transformations in pectoralfin morphology within the Actinopterygii.     

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 ( U _P-C) of Cymatogaster aggregata occurred at a higher speed (measured in bodylengths s⁻¹) for smaller fish than larger fish. At U _P-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 U _P-C) the pectoral fin-beat frequency was independent of the size of the fish. Inter-specific comparisons of U _P-C, pectoral fin-beat frequency and amplitude among C. aggregata, Embiotoca lateralis and Damalichthys vacca showed that C. aggregata had a higher U _P-C than E. lateralis and D. vacca . The pectoral fin-beat frequency at U _P-C showed no significant differences among species. Cymatogaster aggregata achieved higher U _P-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.     

Functional Morphology of Aquatic Flight in Fishes: Kinematics, Electromyography, and Mechanical Modeling of Labriform Locomotion

Labriform locomotion is the primary swimming mode for many fishesthat use the pectoral fins to generate thrust across a broadrange of speeds. A review of the literature on hydrodynamics,kinematics, and morphology of pectoral fin mechanisms in fishesreveals that we lack several kinds of morphological and kinematicdata that are critical for understanding thrust generation inthis mode, particularly at higher velocities. Several needsinclude detailed three-dimensional kinematic data on speciesthat are pectoral fin swimmers across a broad range of speeds,data on the motor patterns of pectoral fin muscles, and thedevelopment of a mechanical model of pectoral fin functionalmorphology. New data are presented here on pectoral fin locomotionin Gomphosus varius, a labrid fish that uses the pectoral finsat speeds of 1 –6 total body lengths per second. Three-dimensionalkinematic data for the pectoral fins of G. varius show thata typical "drag-based" mechanism is not used in this species.Instead, the thrust mechanics of this fish are dominated bylift forces and acceleration reaction forces. The fin is twistedlike a propeller during the fin stroke, so that angles of attackare variable along the fin length. Electromyographic data onsix fin muscles indicate the sequence of muscle activity thatproduces antagonistic fin abduction and adduction and controlsthe leading edge of the fin. EMG activity in abductors and adductorsis synchronous with the start of abduction and adduction, respectively,so that muscle mechanics actuate the fin with positive work.A mechanical model of the pectoral fin is proposed in whichfin morphometrics and computer simulations allow predictionsof fin kinematics in three dimensions. The transmission of forceand motion to the leading edge of the fin depends on the mechanicaladvantage of fin ray levers. An integrative program of researchis suggested that will synthesize data on morphology, physiology,kinematics, and hydrodynamics to understand the mechanics ofpectoral fin swimming.     

Pectoral fin size in a fish species with paternal care: a condition-dependent sexual trait revealing infection status

1. The three-spined stickleback, Gasterosteus aculeatus L., is a territorial fish with exclusive male parental care. Males oxygenate the eggs with fanning movements of their pectoral fins. The present authors investigated whether the apparent sexual differences in the functional demands of the pectoral fins have resulted in sexual differences in fin size. If males have relatively larger pectoral fins, females may use this as a signal to aid their mate choice for good fathers. Therefore, further objectives were to study the condition-dependency of relative pectoral fin size in males and the relationship with male parasite load. 2. Reproductively active males possessed relatively larger pectoral fins than females in both wild-caught and laboratory-bred fish. 3. In the field, caring males with relatively large pectoral fins were in better physical condition and had more food in their stomachs. 4. Relatively small pectoral fins and poor body condition were associated with infection by the intestinal parasite Pomphorhynchus laevis (Acanthocephala), the prevalent parasite species in the study population.     

Effect of an Artificial Caudal Fin on the Performance of a Biomimetic Fish Robot Propelled by Piezoelectric Actuators

This paper addresses the design of a biomimetic fish robot actuated by piezoeeramic actuators and the effect of artificial caudal fins on the fish robot＇s performance. The limited bending displacement produced by a lightweight piezocomposite actuator was amplified and transformed into a large tail beat motion by means of a linkage system. Caudal fins that mimic the shape of a mackerel fin were fabricated for the purpose of examining the effect of caudal fm characteristics on thrust production at an operating frequency range. The thickness distribution of a real mackerel＇s fin was measured and used to design artificial caudal fins. The thrust performance of the biomimetic fish robot propelled by fins of various thicknesses was examined in terms of the Strouhal number, the Froude number, the Reynolds number, and the power consumption. For the same fm area and aspect ratio, an artificial caudal fin with a distributed thickness shows the best forward speed and the least power consumption.