Tail Beat Research Articles

Seasonal variation in activity and nearshore habitat use of Lake Trout in a subarctic lake

BackgroundIn lake ecosystems, predatory fish can move and forage across both nearshore and offshore habitats. This coupling of sub-habitats, which is important in stabilizing lake food webs, has largely been assessed from a dietary perspective and has not included movement data. As such, empirical estimates of the seasonal dynamics of these coupling movements by fish are rarely quantified, especially for northern lakes. Here we collect fine-scale fish movement data on Lake Trout (Salvelinus namaycush), a predatory cold-water fish known to link nearshore and offshore habitats, to test for seasonal drivers of activity, habitat use and diet in a subarctic lake.MethodsWe used an acoustic telemetry positioning array to track the depth and spatial movements of 43 Lake Trout in a subarctic lake over two years. From these data we estimated seasonal 50% home ranges, movements rates, tail beat activity, depth use, and nearshore habitat use. Additionally, we examined stomach contents to quantify seasonal diet. Data from water temperature and light loggers were used to monitor abiotic lake conditions and compare to telemetry data.ResultsLake Trout showed repeatable seasonal patterns of nearshore habitat use that peaked each spring and fall, were lower throughout the long winter, and least in summer when this habitat was above preferred temperatures. Stomach content data showed that Lake Trout acquired the most nearshore prey during the brief spring season, followed by fall, and winter, supporting telemetry results. Activity rates were highest in spring when feeding on invertebrates and least in summer when foraging offshore, presumably on large-bodied prey fish. High rates of nearshore activity in fall were associated with spawning. Nearshore habitat use was widespread and not localized to specific regions of the lake, although there was high overlap of winter nearshore core areas between years.ConclusionsWe provide empirical demonstrations of the seasonal extent to which a mobile top predator links nearshore and offshore habitats in a subarctic lake. Our findings suggest that the nearshore is an important foraging area for Lake Trout for much of the year, and the role of this zone for feeding should be considered in addition to its traditional importance as spawning habitat.

On the influence of head motion on the swimming kinematics of robotic fish.

Up to now bio-inspired fish-mimicking robots fail when competing with the swimming performance of real fish. While tail motion has been studied extensively, the influence of the head motion is still not fully understood and its active control is challenging. In this experimental study, we show that head yawing strongly impacts on the propulsion force and determines the optimal fin actuation amplitude and tail beat frequency when aiming for a maximal propulsion force. In a parametric experimental study on a tethered 367 mm long fish robot the pivot point location of the head yaw has been varied along with tail beat frequency and actuation amplitude. The experiments took place in a still water tank and the swimming force has been measured with a single axis load cell. The robot is actuated with non-conventional area actuators based on micro fiber composites. 105 parameter sets have been investigated while the highest pivot point distance of roughly 0.36 body length from the nose tip provided the highest propulsion force of 500 mN with the lowest actuation frequency of 2.5 Hz and the highest head motion amplitude of a magnitude of 0.18 body length. Even though the pivot point location on a free swimming robot is a consequence of the complex fluid-structure interactions of fish and fluid, the results provide valuable information for the design of fish mimicking robots and questions the paradigm that head yaw is a simple recoil effect from tail motion and has to be minimized for an effective propulsion.

Effects of body stiffness on propulsion during fish self-propelled swimming

Many fish propel themselves using wave-like lateral flexion of their body and tail in the water. The undulatory body is driven by the distributed muscles, and locomotion is achieved by internal muscular stimulation and the external action of the fluid. As one of the material properties, the stiffness of the body being propelled plays an important role in the deformation process, especially for the muscle power input and phase lag. In this paper, a three-dimensional self-propelled elongated body model is employed to numerically investigate the effects of stiffness on the propulsion performance, including the forward speed, energy consumption, and energy-utilization ratio. According to various deformation characteristics and energy-utilization ratios, three deformation modes corresponding to high, medium, and low stiffness are identified. Our results indicate that a deforming body with medium stiffness has the highest efficiency, and its corresponding deformation is closest to that of fish in nature. When the stiffness of the fish body is higher than the normal level, more muscle energy is needed to sustain the tail beating of the same amplitude. A lower level of stiffness produces a more obvious phase lag in the fish body, which might lead to slow control responses. We also show that the stiffness of the fish body affects the scaling relationship between the swimming speed and the tail beating velocity. The upper and lower limits of the scaling exponent correspond to high and low levels of stiffness, respectively, and are also affected by the wavelength of the muscle contraction.

Ontogenetic Plasticity in Shoaling Behavior in a Forage Fish under Warming.

Shoaling behavior is known to increase survival rates during attacks from predators, minimize foraging time, favor mating, and potentially increase locomotor efficiency. The onset of shoaling typically occurs during the larval phase but it is unclear how it may improve across ontogenetic stages in forage fishes. Warming is known to increase metabolic rates during locomotion in solitary fish, and shoaling species may adjust their collective behavior to offset the elevated costs of swimming at higher temperatures. In this study, we quantified the effects of warming on shoaling performance across ontogeny of a small forage fish, zebrafish (Danio rerio) at different speeds. Shoals of larval, juvenile, and adult zebrafish were acclimated at two temperatures (28○C and 32○C), and metabolic rates were quantified prior and following non-exhaustive exercise at high speed. Shoals of 5 individuals were filmed in a flow tank to analyze kinematics of collective movement. We found that zebrafish improve shoaling swimming performance from larvae to juveniles to adults. In particular, shoals become more cohesive, and both tail beat frequency and head-to-tail amplitude decrease with ontogeny. Early life stages have higher thermal sensitivity in metabolic rates and tail beat frequency especially at high speeds, when compared to adults. Our study shows that shoaling behavior and thermal sensitivity improve as zebrafish shift from larval to juvenile to adult stages.

Effects of water temperature on swimming performance of Siniperca knerii Garman under the Yuanshui River cascade development

We examined the swimming parameters and oxygen consumption rate at four temperature levels (15，20，25 and 30°C) of Siniperca knerii Garman (11.81 ±2.21 cm, 26.4 ± 6.28g) from Yuanshui River for 30 days to analyze the ecological adaptability of the typical fish and the conservation of fishery resources from the Dongting Lake water system. Their relationship was also analyzed, and the results showed an approximately linear increasing trend of the fish’s critical swimming speed and preferred swimming speed with the change of temperature (P<0.05). In contrast, the induction velocity of fish decreased with the increase in water temperature. The relative induction velocities of the fish at four temperatures were (1.16±0.07), (0.94±0.06), (0.86±0.07), and (0.70±0.09) BL/s (Body Length/s). The preferred swimming speed was (1.86±0.04), (2.23±0.35), (2.65±0.28), and (2.74±0.33) BL/s. The relative critical speed was (2.58 ±0.32), (3.31±0.41), (4.31±0.52), and (5.22±0.48) BL/s. According to oxygen consumption rate at different temperatures, four nonlinear function models of the relationship between oxygen consumption rate of water temperature and swimming speed behavior parameters were obtained by nonlinear fitting. The model proved that the oxygen consumption rate, tail beating frequency, and respiratory rate increased with the increase in swimming speed. The higher the temperature, the more significant the changes were. The results showed that water temperature significantly affected the swimming characteristics of juvenile Siniperca knerii Garman. The changes were due to physiological and biochemical regulation with temperature and environmental changes. This experiment provided essential data support for the adaptive mechanism of sports physiology and ecology of typical fishes in the Yuanshui River.

Regulation of the swimming kinematics of lampreys Petromyzon marinus across changes in viscosity.

The bodies of most swimming fishes are very flexible and deform as result of both external fluid dynamic forces and internal musculoskeletal forces. If fluid forces change, the body motion will also change unless the fish senses the change and alters its muscle activity to compensate. Lampreys and other fishes have mechanosensory cells in their spinal cords that allow them to sense how their body is bending. We hypothesized that lampreys (Petromyzon marinus) actively regulate body curvature to maintain a fairly constant swimming waveform even as swimming speed and fluid dynamic forces change. To test this hypothesis, we measured the steady swimming kinematics of lampreys swimming in normal water, and water in which the viscosity was increased by 10 or 20 times by adding methylcellulose. Increasing the viscosity over this range increases the drag coefficient, potentially increasing fluid forces up to 40%. Previous computational results suggested that if lampreys did not compensate for these forces, the swimming speed would drop by about 52%, the amplitude would drop by 39%, and posterior body curvature would increase by about 31%, while tail beat frequency would remain the same. Five juvenile sea lampreys were filmed swimming through still water, and midlines were digitized using standard techniques. Although swimming speed dropped by 44% from 1× to 10× viscosity, amplitude only decreased by 4%, and curvature increased by 7%, a much smaller change than the amount we estimated if there was no compensation. To examine the waveform overall, we performed a complex orthogonal decomposition and found that the first mode of the swimming waveform (the primary swimming pattern) did not change substantially, even at 20× viscosity. Thus, it appears that lampreys are compensating, at least partially, for the changes in viscosity, which in turn suggests that sensory feedback is involved in regulating the body waveform.

Impacts of Deoxygenation and Hypoxia on Shark Embryos Anti-Predator Behavior and Oxidative Stress.

Climate change is leading to the loss of oxygen content in the oceans and endangering the survival of many marine species. Due to sea surface temperature warming and changing circulation, the ocean has become more stratified and is consequently losing its oxygen content. Oviparous elasmobranchs are particularly vulnerable as they lay their eggs in coastal and shallow areas, where they experience significant oscillations in oxygen levels. Here, we investigated the effects of deoxygenation (93% air saturation) and hypoxia (26% air saturation) during a short-term period (six days) on the anti-predator avoidance behavior and physiology (oxidative stress) of small-spotted catshark (Scyliorhinus canicula) embryos. Their survival rate decreased to 88% and 56% under deoxygenation and hypoxia, respectively. The tail beat rates were significantly enhanced in the embryos under hypoxia compared to those exposed to deoxygenation and control conditions, and the freeze response duration showed a significant opposite trend. Yet, at the physiological level, through the analyses of key biomarkers (SOD, CAT, GPx, and GST activities as well as HSP70, Ubiquitin, and MDA levels), we found no evidence of increased oxidative stress and cell damage under hypoxia. Thus, the present findings show that the projected end-of-the-century deoxygenation levels elicit neglectable biological effects on shark embryos. On the other hand, hypoxia causes a high embryo mortality rate. Additionally, hypoxia makes embryos more vulnerable to predators, because the increased tail beat frequency will enhance the release of chemical and physical cues that can be detected by predators. The shortening of the shark freeze response under hypoxia also makes the embryos more prone to predation.

Muscle fiber plasticity, stress physiology, and muscle transcriptome determine the inter-individual difference of swimming performance in the large yellow croaker (Larimichthys crocea)

Swimming performance is extremely important to critical activities of fishes, such as foraging, anti-predator, and migration. As one of primary stock enhancement fish species in China, it is imperative to study on swimming performance of the large yellow croaker (Larimichthys crocea). In the present study, the swimming performance of juvenile large yellow croaker was investigated, including the behavior, muscle morphology, stress physiology, and genetic mechanisms underlying the individual difference. Juveniles of the croaker were individually subjected to the critical swimming speed (Ucrit) test, and thereby divided into fast (36.47 cm/s) and slow (18.65 cm/s) groups. The juveniles in the fast group had significantly higher tail beat frequency, smaller muscle fiber diameter and more muscle fiber number, as well as lower plasma cortisol and corticotropin releasing hormone (CRH) levels than those in the slow group. Meanwhile, expression levels of hsp70 and pcna in the brain were significantly higher in the fast group than in the slow group, however no significant difference was observed in syt1a expression. Furthermore, the key genes and pathways involved in the swimming performance were assessed by mapping the white skeletal muscle transcriptome. We found that a total of 157 transcripts was differentially expressed between the fast and slow groups, enriched in oxidative phosphorylation, glycosaminoglycan biosynthesis, nicotinate and nicotinamide metabolism, cellular senescence, and cardiac muscle contraction pathways. A multitude of mitochondrial NADH dehydrogenase subunits and solute carrier family genes were especially related. In conclusion, we for the first time found that fish swimming performance directly links to muscle fiber plasticity, stress physiology, and molecular base divergence in the large yellow croaker. The present results lay a foundation for ethological-character-based selective breeding for the large yellow croaker in the regards of swimming performance.

Quantal Response and Histopathological Effects of Sub-lethal Concentrations of a Selected Oilfield Chemical on African Catfish (Clarias gariepinus)

The behavioural and histological effects of sublethal concentrations (0.0 ml/L, 12.8 ml/L, 25.59 ml/L, 38.39 ml/L, 51.19 ml/L, and 63.99 ml/L) of Xylene were evaluated in African Catfish (Clarias gariepinus) after 28 days of exposure. Physico-chemical parameters such as temperature, conductivity, hydrogen ion concentration (pH), total hardness, total dissolved solids, dissolved oxygen, total alkalinity, ammonia, and nitrate levels in the experiment were monitored using the standard method. Significant variations were observed in the different units except for the controlled unit. Behavioural changes were observed closely during the sublethal toxicity test using standard procedures. The bioassay experiments were repeated three times and the renewable test method was used. concentrations showed histopathological alterations in the gills and liver. Severely deformations were observed at 12.80ml/l, 38.39ml/l), 51.19ml/l, and 63.99ml/l. No form of abnormalities was observed in the fish gill and liver in the controlled unit. Progressive hyperventilation, faster operculum and tail beat movement, erratic movement, gulping of air, and spiralling. jumping, display of vigorous jerky movement suffocation, and loss of reflex were observed in C. gariepinus exposed to higher sublethal concentrations of Xylene. There was a significant dose-dependent variation in parameters in the experiment. In conclusion, xylene caused an alteration in the histopathological parameters and the behaviour of C. garienpinus. Therefore, we recommend the need for realistic regulatory measures and proper monitoring and sensitization on use to stakeholders.

Development of a Novel Underactuated Robotic Fish with Magnetic Transmission System

In this study, a robotic fish inspired to carangiform swimmers has been developed. The artifact presents a new transmission system that employs the magnetic field interaction of permanent magnets to ensure waterproofness and prevention from any overload for the structure and the actuating motor. This mechanism converts the rotary motion of the motor into oscillatory motion. Such an oscillating system, along with the wire-driven mechanism of the tail, generates the required traveling wave in the robotic fish. The complete free swimming robotic fish, measuring 179 mm in length with a mass of only 77 g, was able to maintain correct posture and neutral buoyancy in water. Multiple experiments were conducted to test the robotic fish performance. It could swim with a maximal speed of 0.73 body lengths per second (0.13 m/s) at a tail beat frequency of 3.25 Hz and an electric power consumption of 0.67 W. Furthermore, the robotic fish touched the upper bound of the efficient swimming range, expressed by the dimensionless Strouhal number: 0.43 at 1.75 Hz tail beat frequency. The lowest energy to travel 1 meter was 4.73 Joules for the final prototype. Future works will focus on endowing the robot with energy and navigation autonomy, and on testing its potential for real-world applications such as environmental monitoring and animal–robot interaction.

Empirical Analysis of the Hugh Gray 'Nessie' Photograph

The first photograph said to be of the Loch Ness Monster was taken on 12th November 1933 around noon by a local man by the name of Hugh Gray. I say "Loch Ness Monster" because I believe the photograph to be genuine and part of the evidence portfolio. The picture that generally circulates is shown below. The Scottish Daily Record took his picture and Mr. Gray gave the following account to them having been interviewed by Hugh Mackenzie (the future Provost of Inverness), Peter Munro representing Hugh Gray's employers at the British Aluminium Company and a Daily Record staff member:
 Four Sundays ago, after church I went for my usual walk near where the river enters the Loch. The Loch was like a mill pond and the sun shining brightly. An object of considerable dimensions rose out of the water not very far from where I was. I immediately got my camera ready and snapped the object which was two or three feet above the surface of the water. I did not see any head, for what I took to be the front parts were under the water, but there was considerable movement from what seemed to be the tail, the part furthest from me. The object only appeared for a few minutes then sank out of sight.
 A contemporary picture of Hugh Gray was printed later which I don't think flatters him much but is shown below to show you the man behind the monster.
 The tenor of the account suggests some throwing up of spray and water as the presumed tail beat about the waters and hence caused some blurriness around that region of the picture. Mackenzie described Gray as a man highly respected by his fellow workmen, employers and locals. Likewise, the Daily Record had the negative examined by four experts who deemed it as untampered. It caused a stir, was panned by zoologists and faded along with general Nessie-lore as the World entered war six years later. Twenty-two years on, Nessie author, Constance Whyte, visited Hugh Gray in May 1955 who was sticking to his story and still had vivid memories of that day plus he also recounted five other times he claimed to have seen the monster over those decades. Renowned monster hunter, Tim Dinsdale, also recounts how he visited Gray in April 1960 and described him as "a most courteous individual" as he took him to the spot of the sighting[4]. He spoke with "complete conviction" about that day as well as maintaining an accuracy of his account. He also added some detail of his other sightings which partly consisted of rapidly moving bow waves with no visible cause. What remains of the photograph today is uncertain.

Aquatic Walking and Swimming Kinematics of Neonate and Juvenile Epaulette Sharks.

The epaulette shark, Hemiscyllium ocellatum, is a small, reef-dwelling, benthic shark that-using its paired fins-can walk, both in and out of water. Within the reef flats, this species experiences short periods of elevated CO2 and hypoxia as well as fluctuating temperatures as reef flats become isolated with the outgoing tide. Past studies have shown that this species is robust (i.e., respiratory and metabolic performance, behavior) to climate change-relevant elevated CO2 levels as well as hypoxia and anoxia tolerant. However, epaulette shark embryos reared under ocean warming conditions hatch earlier and smaller, with altered patterns and coloration, and with higher metabolic costs than their current-day counterparts. Findings to date suggest that this species has adaptations to tolerate some, but perhaps not all, of the challenging conditions predicted for the 21st century. As such, the epaulette shark is emerging as a model system to understand vertebrate physiology in changing oceans. Yet, few studies have investigated the kinematics of walking and swimming, which may be vital to their biological fitness, considering their habitat and propensity for challenging environmental conditions. Given that neonates retain embryonic nutrition via an internalized yolk sac, resulting in a bulbous abdomen, while juveniles actively forage for worms, crustaceans, and small fishes, we hypothesized that difference in body shape over early ontogeny would affect locomotor performance. To test this, we examined neonate and juvenile locomotor kinematics during the three aquatic gaits they utilize-slow-to-medium walking, fast walking, and swimming-using 13 anatomical landmarks along the fins, girdles, and body midline. We found that differences in body shape did not alter kinematics between neonates and juveniles. Overall velocity, fin rotation, axial bending, and tail beat frequency and amplitude were consistent between early life stages. Data suggest that the locomotor kinematics are maintained between neonate and juvenile epaulette sharks, even as their feeding strategy changes. Studying epaulette shark locomotion allows us to understand this-and perhaps related-species' ability to move within and away from challenging conditions in their habitats. Such locomotor traits may not only be key to survival, in general, as a small, benthic mesopredator (i.e., movements required to maneuver into small reef crevices to avoid aerial and aquatic predators), but also be related to their sustained physiological performance under challenging environmental conditions, including those associated with climate change-a topic worthy of future investigation.

Behavioural Toxicity of a Combined Oilfield Chemicals on African Catfish (Clarias gariepinus) (Burchell 1822)

The toxicity of the combination of xylene and diesel at a 50:50 ratio on the African catfish (Clarias gariepinus) was investigated using a static bioassay for 96hrs. No significant difference (P>0.05) was observed in the Physicochemical parameters of the experimental water after exposure for 24 hours among the different concentration gradients and the controlled unit. Although there was an increased variation along the concentration gradient observed after 96hours. The behavioral responses of the test fish from 24-96 hours of exposure show normal behavioral responses in the control. C. gariepinus exposed to 25 ml/l to 50 mg/l concentration of the toxicant showed normal behavior from 24 to 48 hours. Afterward, the fish that were active stopped swimming and remained static for a while in response to the sudden changes in the surrounding environment. Generally, fish exposed to higher concentrations such as 100 ml/l to 250 ml/l of the test chemicals showed progressive hyperventilation and abnormal behavior like gulping air, erratic swimming movement, very fast swimming, jumping, and displaying vigorous jerky movement suffocation, and loss of reflex. A faster operculum and tail beat movement was also observed with Spiraling. The behavioral responses increased significantly (P<0.05) with an increase in concentration per time as compared to the control group of fish. The noticeable behavioural difference was recorded for the different concentrations of the test chemical. An eco-friendly chemical that is within the acceptable limits recommended by WHO and DPR should be used in well stimulation and cleaning for sustainable biodiversity and a healthy aquatic environment.

Sperm tail beating

Sperm tail beating

Sperm tail beating

Sperm tail beating

Sperm tail beating

Sperm tail beating

Lab-on-a-Fish: Wireless, Miniaturized, Fully Integrated, Implantable Biotelemetric Tag for Real-Time In Vivo Monitoring of Aquatic Animals

In vivo electronic monitoring systems for underwater applications are promising technologies for obtaining information about aquatic animals. State-of-the-art devices are constrained by limits on the number of integrated sensors, large dimensions and weight, and short device longevity. Here, we report the Lab-on-a-Fish: the world’s first biotelemetry tag that combines edge computing with wireless sensing of in vivo physiology [electrocardiogram (ECG) and electromyogram (EMG)], behavior [activity level and tail beat frequency (TBF)], and ambient environment (temperature, pressure, and magnetic field). The Lab-on-a-Fish has a miniaturized form (dry weight: 2.4 g; wet weight: 0.8 g; and dimensions: 5.5 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\times }\,\,6.5$ </tex-math></inline-formula> mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\times }\,\,37$ </tex-math></inline-formula> mm) for studying small animals. Engineering efforts spanning improvements in battery chemistry, electronic circuit efficiency, and power-saving algorithms extend the longevity of the device to as much as eight months. The designed piezoelectric transducer and its driving circuit enable underwater wireless communication of multiplexed digital sensor data over a distance up to 400 m. The Lab-on-a-Fish can also store the raw data using flash memory for use in locations that are challenging for acoustic communications or when more complex data postprocessing is needed. Long-term in vivo validation in three species—rainbow trout (Oncorhynchus mykiss), white sturgeon (Acipenser transmontanus), and walleye (Sander vitreus)—demonstrated the device’s sensing potential for biological and environmental applications.

Hydrodynamic Interaction of Two Self-Propelled Fish Swimming in a Tandem Arrangement

Collective locomotion in biological systems is ubiquitous and attracts much attention, and there are complex hydrodynamics involved. The hydrodynamic interaction for fish schooling is examined using two-dimensional numerical simulations of a pair of self-propelled swimming fish in this paper. The effects of different parameters on swimming speed gain and energy-saving efficiency are investigated by adjusting swimming parameters (initial separation distance d0, tail beat amplitude A, body wavelength λ, and period of oscillation T) at different phase difference δϕ between two fish. The hydrodynamic interaction performance of fish swimming in a tandem arrangement is analyzed with the help of the instantaneous vorticity contours, pressure contours, and mean work done. Using elementary hydrodynamic arguments, a unifying mechanistic principle, which characterizes the fish locomotion by deriving a scaling relation that links swimming speed u to body kinematics (A, T, and λ), arrangement of formation (d0), and fluid properties (kinematic viscosity ν), is revealed. It is shown that there are some certain scaling laws between similarity criterion number (Reynolds number (Re) and Strouhal number (St)) and energy-consuming coefficient (CE) under different parameters (Δ). In particular, a generality in the relationships of St–Re and CE–(Re ·Δ) can emerge despite significant disparities in locomotory performance.

Propulsion optimization of a jellyfish-inspired robot based on a nonintrusive reduced-order model with proper orthogonal decomposition

In this research, the propulsion of the proposed jellyfish-inspired mantle undulated propulsion robot (MUPRo) is optimized. To reliably predict the hydrodynamic forces acting on the robot, the proposed nonintrusive reduced-order model (NIROM) based on proper orthogonal decomposition (POD) additionally considers the POD basis that makes an important contribution to the features on the specified boundary. The proposed model establishes a mapping between the parameter-driven motion of the mantle and the evolution of the fluid characteristics around the swimmer. Moreover, to predict new cases where the input needs to be updated, the input of the proposed model is taken from the kinematics of the robot rather than extracted from full-order high-fidelity models. In this paper, it takes approximately 950 s to perform a simulation using the full-order high-fidelity model. However, the computational cost for one prediction with the proposed POD-NIROM is around 0.54 s, of which about 0.2 s is contributed by preprocessing. Compared with the NIROM based on the classic POD method, the proposed POD-NIROM can effectively update the input and reasonably predict the characteristics on the boundary. The analysis of the hydrodynamic performance of the MUPRo pinpoints that, over a certain period and with a certain undulation amplitude, the hydrodynamic force generated by the swinging-like mantle motion (k < 0.5) is greater, outperforming Aequorea victoria in startup acceleration. It is demonstrated that considering a certain power loss and a certain tail beat amplitude, the wave-like mantle motion (k > 0.5) can produce greater propulsion, which means higher propulsion efficiency.

Sex Differences in Mate Choice Preference Characteristics of Aequidens rivulatus.

Simple SummaryGenerally, animals prefer mating with partners of the opposite sex with specific features, which suggests that animals tend to choose mates with particular phenotypic traits. However, there are some differences in mate choice behavior and criteria between males and females. This study analyzed these differences between males and females in Aequidens rivulatus by quantifying body size, behavioral intention, and appearance. The results showed that males paid more attention to preference degree and female attractiveness, whereas females focused on ability and physical strength displays. Consequently, males who chose to mate were primarily associated with body size, behavioral intention, and appearance, whereas the preferences of females were body size, appearance, and behavioral intention. Collectively, our initial findings revealed that males and females have different criteria for mate choice, which is vital in determining successful mating and improving artificial mating.The mating roles of males and females, to a certain extent, are dynamic and variable. Several factors influence the mate choice process. Nonetheless, the main preference features have not yet been fully understood in Aequidens rivulatus. In this study, because of its natural pairing characteristics, A. rivulatus was selected to explore the mate choice preferences of different sexes. Specifically, male and female behavioral performances were described and quantified through a “no-choice paradigm” during mate choice. A total of 12 behavioral performances were defined in male mate choice (experiment 1), whereas 14 behavioral performances were defined in female mate choice (experiment 2). According to the obtained results, unselected females did not display any proactive behaviors in experiment 1, whereas unselected males exhibited proactive behaviors in experiment 2, including quivering, nipping, tail beating, swimming up and down, and aggression. It was also found that both male and female individuals tend to express dislike rather than like. Those behaviors with higher frequencies (e.g., quivering) often mean less energy expenditure, thus easier repeatability. Moreover, principal component analysis (PCA) was employed to extract and identify mate choice preference features. Preliminary results indicated that male preferences for a mate were mainly associated with body size, behavioral intention, and appearance, whereas the intensity of female preferences was in the order of body size, appearance, and behavioral intention. In addition, sex hormone levels were associated with mate choices.