Swimming Speed Research Articles

LUO-V2 and MSPerception: A multi-fin co-drive robotic fish and its multi-sensor-based experimental system

Experimental systems for analyzing robotic fish swimming play a crucial role in optimizing robotic fish, which prompted us to design an experimental system that combines information from multiple sensors to address the shortcomings of current experimental systems with a single measurement. Furthermore, we are interested in a multi-fin co-drive robotic fish. This paper presents the design of a robotic fish, LUO-V2, and an experimental system, MSPerception. The LUO-V2 represents a novel solution for developing multi-fin co-drive robotic fish. It also provides a controller for LUO-V2, which can synchronously control the multi-fin of the robotic fish. Furthermore, the MSPerception system has been designed based on the fusion of multi-sensor information, which can sense the average thrust, swimming speed, and flow field, which provides an effective tool for studying robotic fish swimming. MSPerception was employed to investigate the factors influencing the swimming performance of LUO-V2 and to compare it with the flow field around the caudal fin of a real fish. The experimental results demonstrated that the multi-fin co-drive significantly enhanced the robotic fish’s performance. This research can provide a theorectical foundation for developing multi-fin co-drive robotic fish and experimental systems.

The calculated voyage: benchmarking optimal strategies and consumptions in the Japanese eel’s spawning migration

Eels migrate along largely unknown routes to their spawning ground. By coupling Zermelo’s navigation solution and data from the Japan Coastal Ocean Predictability Experiment 2 (JCOPE2M), we simulated a range of seasonal scenarios, swimming speeds, and swimming depths to predict paths that minimize migration duration and energy cost. Our simulations predict a trade-off between migration duration and energy cost. Given that eels do not refuel during their migration, our simulations suggest eels should travel at speeds of 0.4–0.6 body-length per second to retain enough energy reserves for reproduction. For real eels without full information of the ocean currents, they cannot optimize their migration in strong surface currents, thus when swimming at slow swimming speeds, they should swim at depths of 200 m or greater. Eels swimming near the surface are also influenced by seasonal factors, however, migrating at greater depths mitigates these effects. While greater depths present more favorable flow conditions, water temperature may become increasingly unfavorable, dropping near or below 5 °C. Our results serve as a benchmark, demonstrating the complex interplay between swimming speed, depth, seasonal factors, migration time, and energy consumption, to comprehend the migratory behaviors of Japanese eels and other migratory fish.

Honey Enriched with Additives Alleviates Behavioral, Oxidative Stress, and Brain Alterations Induced by Heavy Metals and Imidacloprid in Zebrafish

Environmental concerns have consistently been a focal point for the scientific community. Pollution is a critical ecological issue that poses significant threats to human health and agricultural production. Contamination with heavy metals and pesticides is a considerable concern, a threat to the environment, and warrants special attention. In this study, we investigated the significant issues arising from sub-chronic exposure to imidacloprid (IMI), mercury (Hg), and cadmium (Cd), either alone or in combination, using zebrafish (Danio rerio) as an animal model. Additionally, we assessed the potential protective effects of polyfloral honey enriched with natural ingredients, also called honey formulation (HF), against the combined sub-chronic toxic effects of the three contaminants. The effects of IMI (0.5 mg·L−1), Hg (15 μg·L−1), and Cd (5 μg·L−1), both individually and in combination with HF (500 mg·L−1), on zebrafish were evaluated by quantifying acetylcholinesterase (AChE) activity, lipid peroxidation (MDA), various antioxidant enzyme activities like superoxide dismutase and glutathione peroxidase (SOD and GPx), 2D locomotor activity, social behavior, histological and immunohistochemical factors, and changes in body element concentrations. Our findings revealed that all concentrations of pollutants may disrupt social behavior, diminish swimming performances (measured by total distance traveled, inactivity, and swimming speed), and elevate oxidative stress (OS) biomarkers of SOD, GPx, and MDA in zebrafish over the 21-day administration period. Fish exposed to IMI and Hg + Cd + IMI displayed severe lesions and increased GFAP (Glial fibrillary acidic protein) and S100B (S100 calcium-binding protein B) protein expression in the optic tectum and cerebellum, conclusively indicating astrocyte activation and neurotoxic effects. Furthermore, PCNA (Proliferating cell nuclear antigen) staining revealed reduced cell proliferation in the IMI-exposed group, contrasting with intensified proliferation in the Hg + Cd group. The nervous system exhibited significant damage across all studied concentrations, confirming the observed behavioral changes. Moreover, HF supplementation significantly mitigated the toxicity induced by contaminants and reduced OS. Therefore, the exposure to chemical mixtures offers a more complete picture of adverse impacts on aquatic ecosystems and the supplementation with bioactive compounds can help to reduce the toxicity induced by exposure to environmental pollutants.

The differences effects of lunges vs. squats exercise programs on the swimming speed 50-meters butterfly style: a quasi-experimental study

Objective: This study aims to investigate the impact of lunges vs. squats exercise on the swimming speed of the 50-meter butterfly stroke among athletes aged 10-13 in KU III and IV categories. Approach: An experimental method employing a two-group pre-test and post-test design was utilized. The study population consisted of athletes affiliated with the SeaRia Aquatic swimming association. Purposive sampling was employed, selecting male swimmers aged 10-13 who were members of the Searia Aquatic swimming club and willing to participate in training during the study. Twenty athletes met the inclusion criteria. The speed test was conducted using the 50-meter butterfly stroke. Statistical data analysis was performed using t-test with SPSS 25 software, employing a significance level of 0.05. Results: The analysis revealed significant effects: (1) lunge training demonstrated a significant improvement in the swimming speed of the 50-meter butterfly stroke among athletes aged 10-13 at the SeaRia Aquatic swimming association (t-count = 6.046, t-table = 2.23, P < 0.05); (2) similarly, squat training led to a significant enhancement in the swimming speed of the 50-meter butterfly stroke among the same age group at the SeaRia Aquatic swimming association (t-count = 6.086, t-table = 2.23, P < 0.05). Collectively, both lunges and squats positively influenced swimming speed in the 50-meter butterfly stroke among athletes aged 10-13 affiliated with the Searia Aquatic swimming association. Conclusion: This study underscores the beneficial effects of incorporating lunges vs. squats into training regimens for young athletes aiming to improve their swimming performance, particularly in the butterfly stroke. This study found that squats are more effective than lunges in improving performance in the butterfly swimming stroke. These findings offer valuable insights for coaches, trainers, and athletes interested in enhancing their competitive edge in swimming, particularly in butterfly style.

Patterns of sperm swimming behaviour depend on male mating tactic and spawning environment in chinook salmon

Many species exhibit alternative mating tactics (ARTs), with larger socially dominant males competing for females and smaller males adopting “sneaker” strategies to exploit fertilisation opportunities without competition or courtship. Females typically prefer larger socially dominant males, but their ability to manipulate mating or fertilisation outcomes is largely unknown. Here, using chinook salmon Oncorhynchus tshawytscha, we examined whether the female’s ovarian fluid (OF) differentially influences the temporal patterns of sperm swimming traits in ejaculates from non-preferred sneaker (‘parr’) and preferred (dominant) males. Results demonstrate that OF improves sperm swimming speed and linearity compared to river water, regardless of male mating tactic. We report a novel tactic-specific difference in sperm linearity in which parr male sperm initially maintain straighter trajectories in river water, compared to dominant males, but then rapidly change to less linear and more circular paths over time. Intriguingly, we show that OF counteracts this change in sperm linearity in parr males so that patterns become indistinguishable from dominants when parr sperm swim in OF. Together, these results show that male chinook salmon exhibit differential sperm trait investment strategies depending on reproductive tactic.

A typology of potential hydraulic barriers to adult salmon migration in a bedrock river

Adult Pacific salmon (Oncorhynchus spp.) in the Fraser River, British Columbia, can die trying to retrace and ascend the river network to their natal spawning grounds due to hydraulic barriers, where encounter velocities exceed swim speeds of adult salmon. We evaluated river hydraulics, river morphology, and swimming ability to better understand these potential hydraulic barriers. A 375 km centerline velocity survey of the Fraser Canyon identified 22 high velocity locations where the distribution of velocity within the reach could produce a hydraulic barrier. We identified and studied three flow types associated with these 22 high velocity locations: 1) plunging flows, 2) rapids, and 3) overfalls, using drone footage at various discharges to examine flow structure and compare surface velocities with swimming modes. Complex flow within the major hydraulic features highlight the spatial locations requiring anaerobic swimming and areas of potential recovery that change with discharge. This approach can be used to improve the understanding of fish migration limits in a natural river system and aid in future mitigation.

Establishment of a dexamethasone-induced zebrafish skeletal muscle atrophy model and exploration of its mechanisms

BackgroundSkeletal muscle atrophy is one of the main side effects of high-dose or continuous use of glucocorticoids (such as dexamethasone). However, there are limited studies on dexamethasone-induced skeletal muscle atrophy in zebrafish and even fewer explorations of the underlying molecular mechanisms. This study aimed to construct a model of dexamethasone-induced skeletal muscle atrophy in zebrafish and to investigate the molecular mechanisms. MethodsZebrafish soaked in 0.01 % dexamethasone solution for 10 days. Loli Track (Denmark) and Loligo Swimming Respirometer were used to observe the effect of dexamethasone on swimming ability. The effects of dexamethasone on zebrafish skeletal muscle were observed by Transmission electron microscopy, H&E, and wheat germ agglutinin techniques. Enriched genes and signaling pathways were analyzed using Transcriptome sequencing. Further, the levels of mitochondrial and endoplasmic reticulum-related proteins were examined to investigate possible mechanisms. Results0.01 % dexamethasone reduced zebrafish skeletal muscle mass (p < 0.05), myofibre size and cross-sectional area (p < 0.001), and increased protein degradation (ubiquitination and autophagy) (p < 0.05). In addition, 0.01 % dexamethasone reduced the swimming ability of zebrafish, as evidenced by the reluctance to move, fewer movement trajectories, decreased total distance traveled (p < 0.001), average velocity of movement (p < 0.001), oxygen consumption (p < 0.001), critical swimming speed (p < 0.01) and increased exhaustive swimming time (p < 0.001). Further, 0.01 % dexamethasone-induced mitochondrial dysfunction (decreased mitochondrial biogenesis, disturbs kinetic homeostasis, increased autophagy) and endoplasmic reticulum stress. Conclusions0.01 % dexamethasone induces skeletal muscle atrophy and impairs the swimming ability of zebrafish through mitochondrial dysfunction and endoplasmic reticulum stress.

Assessing the chronic toxicity of climbazole to Daphnia magna: Physiological, biochemical, molecular, and reproductive perspectives

The widespread use of climbazole (CBZ) has led to its increased presence in aquatic environments, potentially threatening freshwater ecosystems. However, evidence regarding the harmful effects of CBZ on aquatic organisms remains limited. In this study, Daphnia magna was exposed to CBZ at concentrations of 0, 0.2, 20, and 200 μg/L for 21 days to evaluate its chronic toxicity through assessment of life-history traits, physiological parameters, biochemical analyses, and gene expression. The results indicated that CBZ exposure delayed the days to the first brood, reduced the frequency of molting per adult, decreased the offspring number at first brood, diminished the body length, and decreased both the total number of broods per female and the total number of offspring per female. Additionally, CBZ inhibited the swimming speed, filtration rate, and ingestion rate. Moreover, CBZ altered the levels of superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH), while increasing malondialdehyde (MDA) levels. Gene expression analysis revealed varied responses in mRNA levels related to metabolic detoxification (cyp360a8, gst, and p-gp), digestive enzymes (α-amylase, α-esterase, and trypsin), energy (ak), oxygen transport (dhb), and reproduction (nvd, cyp314, ecr, vtg, and jhe) following CBZ exposure. These results indicate that the presence of CBZ in aquatic environments can induce toxicity by altering energy acquisition, supply, and metabolism; impairing metabolic detoxification pathways; eliciting oxidative stress; and causing reproductive toxicity in D. magna.

Effects of Successive Annual Training on Young Swimmers’ Strength Asymmetries and Performance

This study aimed to compare changes in swimmers’ performance, biomechanical variables, and strength asymmetries within two successive training years. Eight competitive age-group swimmers (four males and four females; age: 14.8 ± 1.3 years) were tested before and after the same 12-week mesocycle period within two successive years (Year-1, Year-2). The swimmers were timed in 50, 200, and 400 m, and the stroke rate (SR), stroke length (SL), and stroke index (SI) were calculated. SI was calculated by the product of SL with swimming speed. Dryland shoulder isometric strength (ISO), hand grip isometric strength test (HG), and in-water maximum 30 s tethered swimming force (TF) were evaluated. The asymmetry index was calculated using ISO, HG, and TF tests as [(Fd − Fnd)/0.5 × (Fd + Fnd)] × 100, where Fd is strength in the dominant hand and Fnd is strength in the non-dominant hand. Performance time improved in 200 and 400 m, while the asymmetry indices calculated by the ISO, HG, and TF tests were similar after 12 weeks of training in both Year-1 and Year-2 (p = 0.01). Changes (Δ) in HG strength asymmetries correlated with Δ in 200 and 400 m in Year-2 (r = 0.78–0.87, p = 0.01). The asymmetry index does not change after two successive years of training but may be connected to performance changes in 200 and 400 m front crawl.

A piezoelectric driven amphibious microrobot capable of fast and controllable movement

Abstract Due to its excellent adaptability to the environment and flexibility in narrow spaces, amphibious microrobots have become an important research direction recently. This study proposes an amphibious microrobot driven by piezoelectric actuators with a body length of 4.5 cm and a mass of 1.4 g. The microrobot consists of two active front legs, two passive rear legs, two caudal fins, and a support frame. Each front leg and each caudal fin are designed as structures integrated with their respective piezoelectric actuators. The microrobot has a tilted body, and the ground exerts an oblique upward impact force that makes it jump forward when its front legs swing backwards. The opposite swing of the two caudal fins generates propulsion for swimming. The components of the microrobot are manufactured based on the monolithic laminate process. The monolithic front actuator-leg and monolithic actuator-fin both emerge from a multi-layer material laminate. The support frame is designed and fabricated as a monolithic structure to improve assembly accuracy and reduce redundant assembly steps. The manufactured microrobot demonstrates its flexible and fast amphibious movements. Its maximum land walking speed reaches 15.3 cm/s and its turning speed reaches 48.2 degrees per second. The microrobot has a maximum payload capacity of 5 g moving on land. When the front legs and caudal fins work simultaneously, its underwater swimming speed reaches 9.1 cm/s, and the maximum turning speed is 20.5 degrees per second. The microrobot also confirms a maximum payload of 3 g during its underwater movement.&amp;#xD;

Long-term exposure to environmentally relevant Bisphenol-A levels affects growth, swimming, condition factor, sex ratio and histology of juvenile zebrafish

Bisphenol A (BPA) is an environmental estrogen which perturbs hormone signaling pathways adversely affecting aquatic organisms. To evaluate the impact of developmental exposure to long term yet environmentally relevant low doses of BPA, wild-type juvenile zebrafish of 35 days post fertilization were treated with BPA (1 and 10 µg/L), treatment control (0.5% v/v methanol) and control for 60 days. Both BPA treatments led to significantly increased morality overtime. Length increment and specific growth rates became significantly high in BPA exposed zebrafish overtime. Obesogenic property of BPA was not evident with longexposure to low BPA doses. A significantly high and BPA dose-dependent female-biased sex ratios were observed following the juvenile exposure. Significantly low swimming speed was recorded in the fish of both BPA-treated tanks than that of control. Condition factor was significantly low in BPA exposed fish indicating the poor-wellness. There were numerous histopathological alterations of gonads, liver and kidney indicating impacts of juvenile exposure in zebrafish. Altered growth, swimming, mortality, feminization and histopathological changes in zebrafish induced by BPA indicate the risks associated with developmental exposures. The findings call for more comprehensive studies to comprehend the ecological risks imposed by low concentrations of environmental estrogens in urban aquatic ecosystems.

Long-Term Neurotoxic Effects and Alzheimer's Disease Risk of Early EHDPP Exposure in Zebrafish: Insights from Molecular Mechanisms to Adult Pathology.

2-Ethylhexyl diphenyl phosphate (EHDPP), ubiquitously monitored in environmental media, is highly bioaccumulative and may pose long-term risks, even after short-term exposure. In this investigation, larval zebrafish were exposed to 0.05, 0.5, and 5.0 μg/L EHDPP from 4 to 120 h postfertilization (hpf) to examine the long-term neurotoxicity effects of early exposure. Exposure to 5.0 μg/L EHDPP yielded hyperactive locomotor behavior, which was characterized by increased swimming speed, larger turning angles, and heightened sensitivity to light-dark stimulation. The predicted targets of EHDPP (top 100 potential macromolecules) were primarily associated with brain diseases like Alzheimer's disease (AD). Comparisons of differentially expressed genes (DEGs) from AD patients (GSE48350) and RNA-seq data from EHDPP-exposed zebrafish confirmed consistently abnormal regulatory pathways. EHDPP's interaction with M1 and M5 muscarinic acetylcholine receptors likely disrupted calcium homeostasis, leading to mitochondrial dysfunction and neurotransmitter imbalance as well as abnormal locomotor behavior. Especially, 5.0 μg/L EHDPP exposure during early development (4-120 hpf) triggered early- and midstage AD-like symptoms in adulthood (180 dpf), characterized by cognitive confusion, aggression, blood-brain barrier disruption, and mitochondrial damage in brains. These findings provide deep insights into the long-term neurotoxicity effects and Alzheimer's disease risks of early EHDPP exposure at extremely low dosages.

Surface-active microrobots can propel through blood faster than inert microrobots

Abstract Microrobots that can move through a network of blood vessels have promising medical applications. Blood contains a high volume fraction of blood cells, so in order for a microrobot to move through the blood, it must propel itself by rearranging the surrounding blood cells. However, swimming form effective for propulsion in blood is unknown. This study shows numerically that a surface-active microrobot, such as a squirmer, is more efficient in moving through blood than an inert microrobot. This is because the surface velocity of the microrobot steers the blood cells laterally, allowing them to propel themselves into the hole they are digging. When the microrobot size is comparable to a red blood cell or when the microrobot operates under a low Capillary number, the puller microrobot swims faster than the pusher microrobot. The trend reverses under considerably smaller microrobot sizes or high Capillary number scenarios. Additionally, the swimming speed is strongly dependent on the hematocrit and magnetic torque used to control the microrobot orientation. A comparative analysis between the squirmer and Janus squirmer models underscores the extensive applicability of the squirmer model. The obtained results provide new insight into the design of microrobots propelled efficiently through blood, paving the way for innovative medical applications.

Exploring Sound Frequency Detection in the Golden Rabbitfish, Siganus guttatus: A Behavioral Study.

This study investigates the auditory capabilities of Golden Rabbitfish (Siganus guttatus) and the potential efficacy of sound-based deterrent methods for behavior control. Behavioral experiments were conducted on Golden Rabbitfish to assess their responses to sound stimuli. Sinusoidal pulses in the range of 100~800 Hz, based on previous research on auditory evoked potentials (AEPs), were utilized. An analysis of behavioral trajectories, swimming speed, and acceleration changes revealed the fish's reactions to varying frequency sound stimuli. The results indicate that Golden Rabbitfish exhibited increased swimming activity and speed when stimulated by sound and notably moved away from the source under prolonged exposure to low-frequency acoustic signals. Specifically, the fish displayed the most significant response to 200 Hz sinusoidal pulses with a response threshold of 113~126 dB. These findings suggest that Golden Rabbitfish are particularly sensitive to low-frequency noise, aligning with AEP study outcomes. This study concludes that employing sound stimuli to deter Golden Rabbitfish in practical settings holds promise for mitigating economic losses in seaweed farming due to Golden Rabbitfish grazing.

Respiratory Intervals and Swimming Speed as Remotely Sensed Health Metrics in Free-Ranging Killer Whales (Orcinus orca).

Respiratory rate (mean number of breaths per minute) and respiratory interval (mean time between breaths) can offer insight into a diving mammal's activity state, metabolic rate, behavior, and synchronization due to social cohesion. Also, respiratory rate can reflect an individual animal's health and has the potential to be an informative remotely assessed health metric for monitoring individual animal health in endangered whale species and populations such as southern resident killer whales (Orcinus orca). Using data collected from noninvasive, land-based theodolite tracking, we analyzed swimming speed and surfacing intervals (i.e., mean dive time or mean time between breaths) from 20,613 surfacings of 98 individuals from two populations of the fish-eating, resident killer whale ecotype, namely, one growing (northern resident) and one declining and endangered (southern resident) population. Focal animal sampling was used to measure behavior of individuals of known age and sex in various activity states. Our objective was to evaluate variability and generate normal ranges for respiratory intervals and swimming speeds for killer whales of the Northeast Pacific Ocean resident, fish-eating ecotype to identify baseline respiratory intervals. We found that median respiratory intervals for fish-eating killer whales were between 26 and 29 s for all activity states and that swimming speeds varied by activity state. Median swimming speeds were similar for foraging and traveling (1.6 and 1.7 m/s, respectively), but were significantly slower during resting (1.1 m/s) and social activity (1.3 m/s) states. Three southern resident killer whales in poor body condition (had body condition scores in the lowest 20th percentile of the population) swam at reduced speeds and had shorter median respiratory intervals than outwardly healthy whales of similar age and sex. Respiratory rates, respiratory intervals, and swimming speeds are valuable remotely sensed metrics of health for free-swimming killer whales, especially when combined with other metrics as is the standard in veterinary examinations.

Near maximally swimming schoolmaster snapper (Lutjanus apodus) have a greater metabolic capacity, and only a slightly lower thermal tolerance, than when tested at rest.

To assess the relationship among various measures of thermal tolerance and performance suggested for use in fish, we determined the critical thermal maximum (CTmax), Ucrit, maximum thermal tolerance while swimming [CTSmax] and realistic aerobic scope (ASR) of juvenile schoolmaster snapper (Lutjanus apodus). Their CTSmax (37.5±0.1°C) was only slightly lower than their CTmax (38.9±0.1°C), and this is likely because their maximum metabolic rate (MMR) and ASR during the former test were∼42 and 65% higher, respectively. Further, we did not observe a transition to unsteady (i.e., anaerobically fueled) swimming in the CTSmax test as we did in the Ucrit protocol. These data strongly suggest that thermal tolerance tests on fishes whose lifestyle involves schooling or sustained activity should be performed at ecologically-relevant swimming speeds. Further, they do not support the hypothesis that failure during a CTSmax test is due to a fish's inability to meet its tissue oxygen demands.

An Experimental Approach for the Quantitative Assessment of Downstream Swimming Fish Behavior

ABSTRACTBehavior of fish influences the mortality risk during turbine and pump passages. Knowledge about species‐specific behavior and its triggers is necessary for improving numerical models and the development of autonomous sensor probes to estimate fish mortality in turbines and pumps. A primary objective of the RETERO project is the study of fish behavior in hydraulic conditions similar to turbine and pump intakes in controlled conditions. For this purpose, an experimental conduit was constructed at the Hubert‐Engels Laboratory of the TUD Dresden University of Technology (Germany) equipped with a 3D camera infrared tracking system. The conduit was designed to model hydraulic conditions typical for turbine and pump intakes. In the experimental setup, the effects of flow velocities exceeding the maximum swim speed of fish, as well as spatial velocity gradients and illumination conditions on the fish behavior are studied. The data from brown trout (Salmo trutta) allow for an analysis of how these fish react to flow accelerations and velocities surpassing their sprint speed, using quantitative metrics for movement and activity. An initial evaluation of these experiments highlights the potential of this approach for further research.

Feeding Behavior and Bait Selection Characteristics for the Portunidae Crabs Portunus sanguinolentus and Charybdis natator

Understanding the feeding behavior of Portunidae crabs with different baits can improve bait selection and is crucial for improving the effectiveness of crab fishing gear. This study, conducted in indoor experimental tanks, used trajectory tracking software and two types of natural baits (mackerel (Scomber australasicus) and squid (Uroteuthis chinensis)) to understand the behavior of Portunus sanguinolentus and Charybdis natator. Spatial distribution results showed that P. sanguinolentus was frequently present in the starting area (S1) and bait area (S3) in the control and treatment groups. However, C. natator was frequently present and concentrated in the S1 area compared to the middle areas S2 and S3, and only in the mackerel treatments were they observed to move to the S3 areas. The spatial distribution results indicate that P. sanguinolentus shows a stronger willingness to explore its surroundings, while C. natator is generally in a stationary, wait-and-see state. The swimming speeds of P. sanguinolentus and C. natator showed different trends. P. sanguinolentus showed continuous movement with no fixed speed when no bait was present in the control groups. However, when treated with mackerel and squid, the average swimming speed of P. sanguinolentus was faster (&gt;5 cm/s) in the first 10 min and showed a more stable movement speed when searching for the baits. C. natator showed a stationary or low movement speed when no bait was present in the control groups. However, when C. natator perceived the presence of the baits in the treatment groups, their movement speed increased in the first 10 min. In addition, there was no significant difference between male and female crabs of P. sanguinolentus and C. natator in movement speed in the control and treatment groups. Compared to C. natator, P. sanguinolentus might be more sensitive to natural baits, as shown by its movement from S1 to S3. The results indicate that the species of Portunidae crabs show different bait selections. Natural baits (mackerel and squid) are recommended for catching P. sanguinolentus in crab fisheries.

Numerical simulation on the interaction of median fins for enhancing vortex dynamics and propulsion performance in fish self-propelled swimming

Studies have shown that fish can enhance propulsion performance by utilizing the interaction between median fins (dorsal, anal, and caudal fins), compared to fish with only caudal fin. However, most of the current studies are based on the fish oscillating in-place, and the analysis of median fins interaction to improve swimming propulsion performance is still insufficient, and the mechanism needs further study. This study applied three-dimensional numerical simulation methods to solve the process of grass carp accelerating from a stationary state to cruising state under different body and median fins combination, as well as different motion parameter models. A comparative quantitative analysis of different models was conducted to assess the impact of median fins interactions on enhancing swimming performance, with a detailed analysis of the hydrodynamic mechanisms and their relationship with vortex dynamics. The results indicated that interactions between median fins could generate significant hydrodynamic benefits, with the fish's average swimming speed increasing up to 4.6 times, thrust up to 33.47%, and swimming efficiency up to 25.48%. This study found that the enhancement of propulsion performance was due to the formation of high-intensity and persistent posterior body vortices by the movements of the dorsal and anal fins, which were captured by the leading-edge of the caudal fin, greatly enhancing the strength of the leading-edge vortex. This study elucidates the hydrodynamic mechanisms of the interaction between median fins and could provide new insights into the efficient swimming mechanism of fish in nature.

A coupled machine-learning-individual-based model for migration dynamics simulation: A case study of migratory fish in fish passage facilities

The extensive development of hydropower projects has notably changed the ecohydrological conditions of fish habitats, affecting fish behavior, including habitat usage and migration, to varying extents. Understanding fish migration dynamics is essential for quantitatively assessing the impact of ecological restoration measures on migratory fish. However, no model has yet demonstrated sufficient accuracy to be considered valuable in ecological restoration engineering. To address this issue, in this article, a coupled machine-learning-individual-based model (ML-IBM) consisting of random forest (RF) and Eulerian–Lagrangian–agent method (ELAM) is constructed for predicting fish migration, aiming to find effective fish passage solutions before implementation. In this study, the passage data of ya-fish (Schizothorax prenanti) in vertical slot fishways (VSFs) is compiled to train ML-IBM to simulate fish migration in fish passage facilities. In movement prediction, the accuracy of swimming behavior classification reaches 83.4 %, and the R² for swimming speed regression exceeds 0.77. Compared with other state-of-the-art migration dynamic models, the proposed ML-IBM achieves the lowest root mean square error (RMSE) of 7.35 and a mean absolute error (MAE) of 6.26 in migration simulation results. Further, RF is used to quantitatively calculate the importance of input features. The contributions of each feature are analyzed and discussed from a hydrodynamic perspective, with the importance ranked as follows: flow velocity (FV) > turbulent kinetic energy (TKE) > total hydraulic strain (THS). This approach enhances the interpretability of the model and provides further insights into the mechanism of fish migration. The results presented in this study have significant implications for informing decision-making in the management of living resources and guiding engineering design processes.