Search Results (43)

Accurate identification and quantitative assessment of fish feeding intensity are pivotal for enhancing aquaculture production efficiency. Currently, feeding intensity is mainly assessed based on fish school feeding images with a single feature, overlooking the interdependencies between individual fish and the fish school’s behavior. Therefore, this paper presents a method based on detecting individual fish heads to characterize the feeding aggregation speed and the average swimming speed of the fish school, thereby quantifying the fish school’s feeding intensity. First, the improved YOLOv11n-ALL model was employed to detect individual fish heads, resulting in improved detection performance, increasing inference speed, and reducing computational complexity. Additionally, feeding aggregation speed and average swimming speed indices for fish schools were constructed by combining the YOLOv11n-ALL model with the ByteTrack algorithm to track and extract the centers of individual fish heads’ detection boxes. Finally, the fish school feeding kinetic energy was assessed using the feeding aggregation speed and average swimming speed dual indices, and the fish school feeding intensity levels were classified according to the feeding kinetic energy. Experimental results reveal that the improved YOLOv11n-ALL model achieved an average detection precision (mAP50) of 94.13% for detecting fish heads, reduced the parameter count by 22.09%, and exhibited a computational complexity of 6.4 GFLOPs. Furthermore, the classification model of fish school feeding intensity, quantified by the dual indices of average swimming speed and feeding aggregation speed, achieved a detection accuracy of 97.41%. This method digitizes detection results, enabling rapid classification of fish school feeding intensity and demonstrating its effectiveness for feeding intensity assessment and the development of scientific feeding strategies. Full article

Hydraulic engineering structures can threaten freshwater fish by entraining them into hazardous areas. Acoustic barriers have been proposed as a non-physical method to guide fish away from these zones. In this study, we investigated the behavioral responses of juvenile grass carp to different acoustic stimuli under semi-natural conditions using outdoor net cages. Four sound types were tested: a 1000 Hz pure tone and three broadband sounds, including Alligator sinensis hissing, pile-driving noise, and outboard motor noise. Behavioral responses were quantified using response frequency, total midline crossings, first-response time, maximum swimming speed, and average swimming speed. The results showed that Alligator sinensis hissing elicited the highest number of midline crossings, representing the strongest behavioral response among all tested sounds. In addition, both Alligator sinensis hissing and outboard motor noise induced significantly stronger avoidance responses than the pure tone or pile-driving noise, as indicated by higher response frequency and faster swimming speeds. Furthermore, manipulation of pulse repetition intervals in the most effective deterrent sounds generated a novel broadband sound, which altered fish distribution patterns and elicited avoidance behavior. These findings indicate that both sound type and temporal structure influence negative phonotaxis behavior in grass carp and provide experimental evidence for the optimization of acoustic barriers in fish management. Full article

Golden pompano (Trachinotus ovatus) ranks among the most commercially important and high-yield marine finfish species in Chinese mariculture. In response to the requirement for monitoring fish in aquaculture, this study employed Adaptive Resolution Imaging Sonar (ARIS) to observe the body length, swimming speed, and spatial distribution of untreated (GI group), anesthetized (GII group), and injured (GIII group) T. ovatus in a small offshore cage (1.5 × 1.5 × 2.5 m³). The results demonstrated that the relative error range of the length measurement of the T. ovatus spanned from −3.24 to 4.35, and there was no significant difference between the observed and actual body lengths (ANOVA, p > 0.05). We failed to detect a significant difference in the average speed between the untreated group and the anesthetized group (ANOVA, p > 0.05; Tukey’s HSD, p > 0.05). The injured fish exhibited a significantly lower swimming speed compared to untreated and anesthetized individuals (ANOVA, p < 0.01; Tukey’s HSD, p < 0.01). Untreated individuals and fish with physical injuries exhibited mean vertical distribution depths of 1.06 ± 0.47 m and 1.70 ± 0.51 m, respectively, with the injured fish occupying a significantly greater water depth than the untreated conspecifics (one-way ANOVA, p < 0.01). There was a highly significant association between the treatment status of the fish (untreated/injured) and the frequency of water layer distribution (χ²(2) = 196.78, p < 0.01). The findings of the present study can furnish specific methodological references for the imaging sonar-based monitoring of T. ovatus within aquaculture cage systems. Nevertheless, the study is subject to several inherent limitations, including a small sample size for the injured group (n = 3), the employment of an artificial injury model, and the confinement of experimental subjects to a closed cage environment; these factors may introduce statistical uncertainty and thus exert a considerable impact on the external validity of the study’s results. Full article

To enhance the flexibility and adaptability of underwater robots in complex environments, this paper designs an octopus-inspired soft underwater robot capable of both bipedal walking and multi-arm swimming. The robot features a rigid–flexible coupling structure consisting of a head module and eight rope-driven soft tentacles and integrates buoyancy adjustment and center-of-gravity balancing systems to achieve stable posture control in both motion modes. Based on the octopus’s bipedal walking and multi-arm swimming mechanisms, this study formulates gait generation strategies for each mode. In walking mode, the robot achieves underwater linear movement, turning, and in-place rotation through coordinated tentacle actuation; in swimming mode, flexible three-dimensional propulsion is realized via synchronous undulatory gaits. Experimental results demonstrate the robot’s peak thrust of 14.1 N, average swimming speed of 8.6 cm/s, and maximum speed of 15.1 cm/s, validating the effectiveness of the proposed structure and motion control strategies. This research platform offers a promising solution for adaptive movement and exploration in unstructured underwater environments. Full article

Animal-borne tags are widely used for tracking and monitoring the movements, behaviour, and ecology of marine animals. Tagging can, however, adversely affect the hydrodynamic force balance and welfare of tagged animals, and consequently, the reliability and accuracy of data, such as by increasing drag, altering swimming characteristics, and reducing the survival rate of tagged animals. Therefore, it is important to understand and quantify the impact of tagging on marine animal hydrodynamics and to optimize the choice of tag and attachment position. In this study, computational fluid dynamics (CFD) modelling is used to simulate the flow around tagged and untagged mako sharks (Lamnidae) across their swim speed range for two dominant tag shapes, tagging sites, and body sizes. The results indicate that fin mounted tags can have a significant impact on shark hydrodynamics and energetic balance, increasing drag between 17.6% and 31.2% for a mako shark (2.95 m fork length) across the range of flow velocities tested (0.5 to 9.1 m/s). In comparison, the optimal tagging site for archival tags attached to the dorsal musculature leads to a minimal increase in drag for the larger sharks (>1.5 m), which becomes considerable for small sharks (1 m fork length; 5.1% to 7.6% increase) and leads to an average energetic cost equivalent to 7% of the daily energetic requirement of an untagged animal. Other aspects of the force balance are considered, which reveal a range of varied and complex effects. Recommendations for animal size thresholds (>1.5 m FL) and refinements of tagging practice are suggested. Full article

Water treatment systems in swimming ponds support the natural self-cleaning capabilities of water based on the functions of repository macrophytes in their regeneration zone and the regulation of the internal metabolism of the reservoirs. As part of the project, a functional modular filtration chamber with system multiplication capabilities was designed and created. This element is dedicated to water treatment systems in natural swimming ponds. The prototype system consisted of modular filtration chambers and pump sections, as well as equipment adapted to the conditions prevailing in the eco-pool. An innovative solution for selective shutdown of the filtration chamber without closing the circulation circuit was also used, which forms the basis of a patent application. A verified high-performance adsorbent, Rockfos^® modified limestone, was used in the filtration chamber. In order to determine the effective filtration rate for three small test ponds with different flow rates (5 m/h, 10 m/h and 15 m/h), the selected physicochemical parameters of water (temperature, pH, electrolytical conductivity, oxygen saturation, total hardness, nitrites, nitrates, and total phosphorus, including adsorption efficiency and bed absorption capacity) were researched before and after filtration. Tests were also carried out on the composition of fecal bacteria and phyto- and zooplankton. Based on high effective phosphorus filtration efficiency of 32.65% during the operation of the bed, the following were determined: no exceedances of the standards for the tested parameters in relation to the German standards for eco-pools (FLL—Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e. V., 2011); lower number of fecal pathogens (on average 393—coliform bacteria; 74—Escherichia coli; 34—fecal enterococci, most probably number/100 mL); the lowest share of problematic cyanobacteria in phytoplankton (<250,000 individuals/dm³ in number and <0.05 µg/dm³—biomass); low chlorophyll a content (2.2 µg/dm³—oligotrophy) and the presence of more favorable smaller forms of zooplankton, an effective filtration speed of 5 m/h. This velocity was recommended in the FLL standards for swimming ponds, which were adopted in this study as a reference for rapid filters. In testing the functional efficiency of a dedicated filtration system for a Type II test pond (50 m²—area and 33 m³—capacity), at a filtration rate of 5 m/h, an average effective phosphorus adsorption efficiency of 18.28–53.98% was observed under the bed work-in-progress conditions. Analyses of other physicochemical water parameters, with appropriate calculations and statistical tests, indicated progressive functional efficiency of the system under bathing conditions. Full article

Understanding the motion behaviors of animals is crucial for unraveling the mechanisms underlying ethology across various domains, such as movement patterns, food detection, and defense strategies. In this study, we devised a simplified method enabling the movement of small animals to be tracked conveniently using high-resolution smartphone videos and freely available tracking software. Employing a laboratory video setup, we traced the swimming trajectory of the small copepod zooplankton Eodiaptomus japonicus, which has a body size of approximately 1 mm. From the tracked position data, we analyzed key motion parameters, including swimming distance, speed, and jump frequency. The results of our video analysis showed that adult female E. japonicus exhibited an average swimming speed of 9.8 mm s⁻¹, displaying a predominant cruising pattern with speeds of around 5.0 mm s⁻¹, punctuated by sporadic jumps, showcasing maximum instantaneous speeds reaching a remarkable 190.1 mm s⁻¹. Our successful tracking of the high-speed swimming copepod not only sheds light on its locomotion dynamics but also underscores the potential to refine this method to study the motion trajectories of diverse animal species. Full article

Background: To cope with their horizontal swimming phases, water polo players use different swimming techniques, such as specific variants of the crawl swimming style. Thus, this study aimed to investigate the swimming skills of young water polo players. Methods: An all-out 25-m sprint swimming test in crawl style was completed by 273 international youth water polo players (age = 14.0 ± 0.8 yrs) in two modalities: basic crawl with the head in the water (25C_HeadIN), and a crawl performed while dribbling the ball (25C_Ball). Results: We registered an average time of 14.79 and 15.64 s for 25C_HeadIN and 25C_Ball, respectively, in which the ball dribbling increased to 5% of the swimming time. A swimming skill index (25C_SIC) was calculated to account for differences in ball dribbling speeds, which, considering our international sample and in the absence of previous data, we could speculate as the first international standard value for 14-year-old male water polo players competing at international level. The averaged values for 25C_SI and 25C_SIC were 0.94 ± 0.04 (a.u.) and 1.52 ± 0.15 (a.u.), respectively. Factor analysis indicated that swimming with and without the ball are structurally distinct technical skills, highlighting the specificity of these water polo players’ abilities. Moreover, the study shows significant differences (p < 0.05) between players from different countries and despite some limitations, its results provide valuable insights for the assessment and development of sprint swimming skills in youth water polo players. Conclusions: In summary, the findings of this research provide practical implications for training, player selection, player development and the optimization of youth water polo player performance. Full article

To maximize the limited space of aquaculture vessels and achieve a more efficient layout for aquaculture compartments at the bow and stern, this study proposes two design schemes: modifying the compartment configuration and removing the deflector baffle. The study focused on the impact of compartment configuration and fish movement on the flow field characteristics under the two proposed schemes. The results showed that the mean flow velocity in the octagonal tanks was higher at jet angles of 30° and 45°, with the trend index ($\gamma$) being more stable at 30°. Within jet angles ranging from 0° to 45°, the mean flow velocity increased with rising jet velocity. Retaining the deflector baffle helped stabilize the flow field, making it more effective than scheme A, which, in turn, outperformed scheme B. In circular tanks, the mean flow velocity was higher at 0° and 15°, with the trend index being more stable at 0°. Retaining the deflector baffle at low jet angles further stabilized the flow field. Retaining the deflector baffle at low jet angles helped maintain high average flow velocity, while at high jet angles, it reduced turbulence. Therefore, scheme A demonstrated a better balance between aquaculture volume and flow field stability. Fish simulation experiments revealed that the presence of fish significantly hinders fluid flow and disrupts the stability of the flow field. In practical aquaculture, the jet angle and the use of deflector baffles should be selected based on the tank geometry, while the jet velocity should be adjusted according to the fish species and their swimming speed to establish a flow environment conducive to fish survival and growth. Full article

The agricultural production process contributes to the global issue of pesticide pollution. Based on the static toxicity test of diuron (DCMU) on Daphnia magna (D. magna) for EC₅₀-48 h, a concentration range of 0.2 to 1 mg/L was set as sublethal concentrations, while lethal concentrations were set at 2 mg/L and 4 mg/L. This study analyzes the toxic response patterns of the swimming behavior indicators of D. magna exposed to different concentrations of DCMU. The results showed that the average speed (V) of D. magna decreased step by step with exposure time, regardless of exposure to sublethal concentration or lethal concentration. However, during the same short-term exposure period, the V of D. magna at lethal concentration was higher than that at sublethal concentration, which indicates that the swimming behavior of D. magna exposed to DCMU may be stimulated and accelerated. Compared to the control group, there is a statistically significant difference in the V of D. magna after short-term exposure, especially showing an extremely significant difference after 5 min of exposure. Evidently, compared to the traditional 48 h static toxicity testing method, the swimming behavior indicators of D. magna show a more sensitive response to DCMU after 5 min of exposure, making it more suitable for rapid toxicity detection. By expanding the range of exposure concentrations, it was found that the V indicator of D. magna responded significantly to a DCMU concentration of 0.05 mg/L after only 5 min of exposure, and a high degree of correlation was observed between the indicator and the exposure concentration. Through nonlinear fitting, the relationship between V and the dose–effect of DCMU toxicity presents an S-shaped curve, with R² > 0.9. Consequently, it becomes possible to study the dose–effect relationship between the changes in the swimming behavior indicators of D. magna and the stress concentration based on this theory. This further establishes a foundation for the development of comprehensive aquatic toxicity rapid detection technology based on the toxic response of swimming behavior indicators. Full article

Different pollutants often coexist in natural environments, making it crucial to monitor and study the ecotoxicological effects of composite pollutants in aquatic environments. Nanoplastics and heavy metals are emerging environmental pollutants that can affect the health of aquatic organisms and threaten human health via the food chain. In this study, zebrafish was employed as a model organism to explore the effects of short-term exposure to polystyrene nanoplastics (PS-NPs) and heavy metal copper ions (Cu²⁺) either individually or in combination on fish behavior. First, the single and combined toxicity of Cu²⁺ and PS-NPs to adult zebrafish was investigated to obtain the LC₅₀ values of the two pollutants at 24, 48, 72, and 96 h. Then, the effects of sub-lethal concentrations of Cu²⁺ (0.06, 0.15, and 0.3 mg/L), PS-NPs (5, 10, and 15 mg/L) and binary mixtures containing Cu²⁺ and PS-NPs (0.06 mg/L + 10 mg/L, 0.15 mg/L + 10 mg/L, and 0.3 mg/L + 10 mg/L) on the swim speed and individual distance of zebrafish within 4 h were studied. The results show that the LC₅₀ value for single exposure of zebrafish to Cu²⁺ decreased with the increase in the exposure time, while PS-NPs showed no significant acute toxicity to zebrafish when the concentration was less than 20 mg/L and the exposure time was less than 96 h. The combined exposure of zebrafish to Cu²⁺ and PS-NPs resulted in a 3.1–32.2% reduction in the LC₅₀ value at different time points compared with Cu²⁺ alone. In the behavioral study, both single and combined exposure to Cu²⁺ and PS-NPs induced hyperactivity and aggregation phenomena in the zebrafish at different levels; the duration of these two phenomena was correlated with the concentration of the pollutants. The combined exposure to Cu²⁺ and PS-NPs exacerbated the behavioral changes in zebrafish compared with exposure to Cu²⁺ alone, reducing their hyperactivity time, average swim speed and aggregation time by 30.7–41.0%, 13.6–15.4%, and 28.3–28.8%, respectively. Therefore, this study indicates that the combined short-term exposure to PS-NPs and Cu²⁺ can exacerbate the toxicity of pollutants, and also proves the feasibility for early warning of combined NPs and heavy metals pollution based on adult zebrafish behavioral indicators. Full article

Background: The main aim of this study was to identify the differences between subgroups of swimmers based on physiological (peak oxygen uptake—VO₂peak), strength (average tethered swimming force—60F_ave), stroke kinematics (v₁₀₀—swimming speed at 100 m front crawl, stroke rate—SR, stroke length—SL), and anthropometrical (i.e.,: biological age—BA, body height—BH, body mass—BM) factors within swimmers at different levels of maturity (BA). Methods: This study involved 39 female swimmers (age: 12.88 ± 0.54 years, BA: 13.98 ± 1.91 years). Cluster analysis (k-cluster) and stepwise multiple regression was performed. Results: Significant correlations were observed between v₁₀₀ and BA, 60F_ave, AS, VO₂peak. Stepwise multiple regression indicated 60F_ave and VO₂peak as the main explanatory variables of v₁₀₀ (R² = 0.60, p < 0.0001). Cluster analysis allowed us to distinguish three groups of swimmers, differing in BA (cluster 1: 14.07 ± 0.96 years, cluster 2: 17.05 ± 1.53, cluster 3: 11.94 ± 0.95) and v₁₀₀, as well as in BH, FFM, AS. Conclusions: There were differences between cluster groups, with early mature swimmers characterized by the highest BH, FFM, AS, 60F_ave, and VO₂peak. Probably, biologically younger late mature swimmers (cluster 3) are slower than the other 2 groups (cluster 1 and 2) because of being less somatically developed. Based on these study results, coaches should ensure further development of aerobic and anaerobic conditioning among normal mature swimmers with simultaneous focus on improving technique skills among early mature ones. Full article

Observation of manta rays exiting water has been rarely reported, as there are various difficulties in observing and obtaining data on their behavior in a marine environment. Therefore, the movement mechanism of manta rays exiting water is still unclear. This paper proposes the idea of using CFD (based on Ansys Fluent, version 2022) to simulate the water-exit process of the manta ray. The study discusses the changes in the mechanical and kinematic parameters of the manta ray over time and obtains the evolution of vortex structures during the underwater movement phase of the manta ray. Time history variations of the mechanical and kinematics parameters in the vertical water-exit motion are discussed. The evolution of vortex structures during the underwater movement of the manta ray is obtained. The direction in which the manta ray approaches the free surface is the X-direction and the direction of its flapping motion is the Z-direction. V_X and V_Z are the velocities of the manta ray in the X- and Z-directions, respectively. F_X and F_Z represent the forces acting on the manta ray in the X- and Z-directions, respectively. The results indicate that the vertical water-exit of the manta ray mainly undergoes three stages: underwater acceleration, crossing the free surface, and aerial movement. During the underwater acceleration phase, the force F_X of the manta ray fluctuates, but its average value is positive within one cycle. V_X also shows a stepwise increase, while F_Z and V_Z exhibit periodic changes. During the stage of crossing the free liquid surface, F_X first increases and then sharply decreases, V_X also shows an increase and then decrease, F_Z fluctuates greatly, producing a peak, and the swimming speed V_Z of the manta ray is negative. During the aerial motion phase, F_X is mainly affected by gravity, V_X decreases linearly, F_Z approaches 0, and V_Z remains constant. During the process of swimming underwater, the tail vortex of the manta ray presents a double row staggered structure to generate thrust. Increasing the flapping frequency and decreasing the wave number can improve the swimming speed of the manta ray, and then increase its water-exit height. The findings may provide an important hydrodynamics basis for biomimetic trans-media vehicle designs. Full article

The high-speed and efficient swimming characteristics of tuna are valuable for designing bio-inspired underwater vehicles. Tuna use their highly deformable caudal fins as propulsors during swimming. Caudal fin deformation is categorized into skeletal-controlled active deformation and fluid-induced flexible passive deformation. To investigate how flexible passive deformation affects propulsion performance, simulations of four caudal fins with varying flexibilities under two $St$ numbers in a uniform flow are conducted using the finite volume method. This study finds that the medium-flexibility caudal fin achieves a higher time-averaged thrust coefficient without sacrificing efficiency under both high and low $St$ numbers. At a high $St$ number, the medium-flexibility caudal fin enhances thrust by reducing detrimental secondary flows. At a low $St$ number, the medium-flexibility caudal fin increases thrust by strengthening vortex rings, which induces a stronger backward jet. Full article

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 (>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. Full article