Search Results (55)

Data of experimental, comparative, and allometric studies was examined in relation to the wider oxygen transport cascade, including branchial ventilation, diffusion across the water–blood barrier, blood oxygen transport, muscle capillarization, and mitochondrial content. Experimental reductions in functional gill area are associated with lower maximal oxygen consumption and reduced critical swimming speed, whereas reversible gill remodelling may increase exposed lamellar surface under hypoxia or increased oxygen demand. Comparative evidence indicates that gill area accounts for a measurable, but incomplete, component of variation in metabolic rate and hypoxia tolerance. A descriptive comparison of ten published paired gill surface area (GSA) and standard metabolic rate (SMR) datasets did not reveal a consistently negative difference between gill surface area and standard metabolic demand across the species and experimental conditions examined. This comparison addresses maintenance metabolism but does not test oxygen-supply constraints during routine or maximal activity. The broader evidence reviewed includes large salmonids with cardiovascular compensation, cyprinids with reversible gill remodelling, haemoglobinless icefishes, and active pelagic taxa with high cardiorespiratory and locomotor investment. Collectively, these examples show that the functional significance of gill area depends on interacting branchial, cardiovascular, haematological, tissue-level, and ecological traits. Full article

Swimming performance and energetics of the Japanese eel (Anguilla japonica) across growth and early migratory phases remain poorly quantified. We used swim-tunnel respirometry to compare selected environmental and developmental contrasts in yellow and early silver eels from the Tone River estuary. Critical swimming speed (U_crit), optimal swimming speed (U_opt), minimum cost of transport (minCOT), oxygen consumption at U_opt, and low-flow MO₂ measured at 0.1 m s⁻¹ were evaluated in sequential freshwater trials at 25 and 18 °C, an exploratory Y2 freshwater–seawater comparison at 18 °C, and a Y2–S1 comparison in seawater at 18 °C. U_crit and low-flow MO₂ were numerically higher under FW25 than FW18, but this contrast was confounded with fixed trial order and fasting history. In Y2 eels, SW18 was associated with higher low-flow MO₂ than FW18, whereas active-speed-derived variables were limited by sample size. Under SW18, no clear stage-associated differences were detected between Y2 and S1 eels. Laboratory-derived U_opt and U_crit exceeded field-estimated active horizontal swimming speeds, but this comparison should be interpreted cautiously. Full article

To evaluate the effects of swimming training on growth, swimming performance, and osmoregulatory-related indices in juvenile coho salmon, freshwater-reared fish were subjected to current of 1 body length per second (BL·s⁻¹) from December 2024 to April 2025. Fork length, body weight, condition factor, insulin-like growth factor-1 (IGF-1), and gill and intestinal Na⁺/K⁺-ATPase (NKA) protein abundance were measured monthly, and critical swimming speed (U_crit) was evaluated after one month of training. Trained fish showed greater fork length in March and higher body weight in March and April than controls. The condition factor was higher in trained fish in February and March, but declined during spring smolt development. Swimming capacity was enhanced by training, as indicated by significantly higher U_crit. Mean IGF-1 levels did not differ between groups, but IGF-1 correlated positively with body size only in trained fish. No significant training effect was detected for either gill or intestinal NKA protein abundance, although gill NKA increased significantly in April, likely reflecting seasonal smoltification. In addition, IGF-1 was significantly correlated with gill NKA in trained fish in March. Collectively, these results indicate that sustained swimming training improves growth and swimming performance and may enhance associations among measured physiological variables during smoltification in juvenile coho salmon. Full article

Total suspended solids (TSS) have been shown to damage the structural integrity of fish gills, impairing their function, including gas exchange. However, studies showing linkages between gill damage due to TSS and fish performance are limited. There is a large diversity of fish species inhabiting aquatic environments, and whether the TSS impact on gill function is similar across a range of species has yet to be explored. Here, we exposed multiple species, including salmonids (rainbow, brook and cutthroat trout) and cyprinids (fathead minnow and longnose dace) to a range of TSS concentrations (0–1000 mg L⁻¹) for 4 d and assessed damages to gill structure (filament thickness, lamellae thickness, oxygen diffusion distance, lamellae length, epithelial lifting, and interlamellar distance) using confocal microscopy. All species tested showed similar gill structural damage, including thicker lamellae, longer oxygen diffusion distances, and reduced respiratory surface area, at concentrations ≥ 100 mg L⁻¹ TSS. To assess whether gill damage corresponds to performance dysfunction, we tested the metabolic rate and swimming capacity of a salmonid (rainbow trout) and a cyprinid (fathead minnow) after exposure to 100 mg L⁻¹ TSS using swim tunnel respirometry. Trout showed lower routine metabolic rate (RMR) and maximum metabolic rate (MMR) after TSS exposure and were unable to reach the higher swimming speeds attained by unexposed fish. Fathead minnows showed no difference in the RMR after TSS exposure, but, like trout, had a lower MMR and were unable to attain the higher swimming speed of the control fish. Both species showed a ~35% reduction in the critical swimming speed (U_crit). These findings reveal that environmentally realistic TSS concentrations damage gill structure, impair fish swimming performance, and may compromise their ability to cope with energy-demanding activities, including additional biotic and abiotic stressors. Full article

The mechanism by which fish enhance hydrodynamic performance through collective swimming is a research hotspot in the field of underwater bionic robots. This study employs the Immersed Boundary-Lattice Boltzmann Method (IB-LBM) to conduct numerical simulations on a two-dimensional, single-degree-of-freedom (1-DOF) autonomous propulsion bionic fish swarm. It systematically investigates the effects of swarm size and inter-individual spacing on swimming speed and cost of transport (CoT) under two typical configurations: series and parallel arrangements. Findings reveal that hydrodynamic benefits are highly dependent on the spatiotemporal evolution of flow field structures. In the series configuration, an optimal spacing range of 1.5 L to 2.0 L exists within the school, where the “wake capture” effect is pronounced. Trailing fish achieve a maximum speed increase of approximately 41.1% while significantly reducing energy consumption. However, as spacing increases to 2.5 L, the cooperative gain for front and middle-row individuals rapidly diminishes, and the lead fish even experiences significant performance loss. Uniquely, the trailing fish in the four-fish formation exhibits distinct flow field reorganization and performance recovery at the 4.5 L trailing position. In the parallel formation, the “channel effect” and “blocking effect” of the fluid dominate. The study identifies 0.4 L laterally as the critical instability spacing under the investigated kinematic regime, where strong destructive interference causes a sharp deterioration in individual swimming performance. Additionally, the parallel formation exhibits pronounced positional differentiation. Central individuals, constrained by dual lateral flow fields, experience restricted lateral wake expansion and accelerated energy dissipation, resulting in significantly weaker escape capabilities from low-speed conditions compared to marginal individuals. The vortex-dynamic mechanism revealed herein provides theoretical foundations for formation control in multi-fish biomimetic cooperative systems. Full article

Background: Stroke rate (SR) is a critical determinant of swimming speed and performance; however, the relationship between upper-limb movement frequency assessed on land and SR in water remains unclear. Methods: This preliminary study examined the association between dry-land upper-limb movement frequency and in-water kinematics in ten male competitive swimmers (15.23 ± 1.06 years). Dry-land upper-limb movement frequency was evaluated through two maximum-effort trials consisting of 10–12 circular arm movements performed under a straight-arm condition (STR_SR) and a swimming-technique-simulated bend-arm condition (TECH_SR). All trials were video-recorded for analysis. In-water testing included a maximum-effort 50 m sprint and 8–12 × 25 m progressively increasing speed tests to elicit maximum swimming speed and maximum SR. SR, swimming speed, stroke length, and stroke index were calculated for all trials. Results: No relationship was observed between dry-land upper-limb movement frequency and SR of the 50 m test (p > 0.05). However, the percentage difference between STR_SR and maximum SR was associated with stroke index at maximum speed (r = −0.66, p = 0.04), maximum SR (r = −0.65, p = 0.04), and swimming speed at maximum SR (r = −0.72, p = 0.01) οf the 8–12 × 25 test. Similarly, TECH_SR was correlated with stroke index at maximum speed, SR, and stroke length in the 8–12 × 25 test (r = −0.67 to −0.71, p = 0.01). Conclusions: These findings suggest that faster and more efficient swimmers exhibit a greater difference between their maximum dry-land movement frequency in upper limbs and the SR adopted in water, allowing a greater potential to adjust in a more comfortable and submaximal manner in water movements. Full article

Biological fish possess the intrinsic ability to dynamically modulate body stiffness to adapt to varying fluid environments, thereby optimizing propulsive efficiency, swimming speed, and maneuverability. In contrast, this capability remains a significant challenge for most existing robotic fish, which typically rely on fixed-stiffness configurations. This article presents a comprehensive review of variable stiffness structures and their applications in biomimetic robotic fish. The associated technologies are systematically classified into four categories: smart material-driven, bio-inspired, fluid-driven, and hybrid-driven mechanisms. A comparative analysis of state-of-the-art prototypes is conducted, evaluating critical performance metrics including physical dimensions, maximum swimming speed, minimum turning radius, maximum turning rate, and Strouhal number. Furthermore, the specific advantages and technical limitations of each variable stiffness category are critically assessed. Finally, existing challenges in current research are identified, and prospective directions are proposed. The review demonstrates that variable stiffness technology offers significant potential to advance the hydrodynamic performance of robotic fish and facilitate their deployment in practical engineering applications. Full article

Objective: This study evaluated whether higher adherence to the Mediterranean Diet (MD), specifically through increased legume consumption, is associated with improved functional, autonomic, and performance parameters in adolescents and young adult competitive swimmers. Methods: Thirty-nine swimmers (mean age 19.7  ±  2.3 years; 22 men, 17 women) monitored over a five-month period under standardized training conditions. Based on baseline dietary assessment, participants were allocated into three groups according to habitual legume intake: Control group (<1 serving/week, no dietary modification), 3Legumes group (~2 servings/week, increased to 3/week), and 6Legumes group (~3–4 servings/week, increased to 6/week). Functional evaluation encompassed bioelectrical impedance parameters (phase angle, extracellular and intracellular water, ECW/ICW ratio), heart rate variability (HRV), cardiac coherence, and critical swimming speed test (CSS) results. Results: After 5 months, the 6Legumes group showed an increase in phase angle (Δ  =  +0.34  ±  0.35°, p =  0.004), a reduction in extracellular water (Δ  =  −1.77  ±  0.93%, p <  0.001), and an increase in intracellular water (Δ  =  +1.77  ±  0.93%, p <  0.001), resulting in a lower ECW/ICW ratio (Δ  =  −0.051  ±  0.028, p <  0.001). HRV (Δ  =  +6.92  ±  5.02, p =  0.0003) and cardiac coherence (Δ  =  +0.40  ±  0.35, p =  0.0015) also demonstrated statistically significant improvements, whereas CSS exhibited a positive trend (Δ  =  +0.011  ±  0.019 m/s, p =  0.067) without reaching statistical significance. Between-group comparisons confirmed significant differences in phase angle and water-distribution parameters (all p <  0.01). Conclusions: In this cohort of adolescents and young adult competitive swimmers, increased legume consumption within a Mediterranean dietary framework was associated with beneficial adaptations in cellular hydration status, autonomic regulation, and functional performance. Full article

Background: Neuromuscular determinants such as maximal force, maximal velocity, and upper-body power are recognized as key contributors to competitive swimming performance. However, despite the relevance of these dry-land qualities, their relationships with the physiological mechanisms underpinning in-water performance, particularly aerobic and anaerobic capacities, remain insufficiently established. Purpose: This study aimed to investigate the relationships between upper-body load–velocity profile parameters (theoretical maximal force: F₀; theoretical maximal velocity: V₀; and maximal power: P_max), aerobic capacity expressed through critical velocity, and anaerobic capacity in trained swimmers. Methods: Thirty competitive male swimmers (age = 16.50 ± 0.31 years) completed an upper-body load–velocity profile test using the bench press exercise to determine F₀, V₀, and P_max. Swimming performances in the 100, 200, and 400 m freestyle events were used to calculate critical velocity and anaerobic capacity based on a linear distance–time model. Pearson correlation coefficients and linear regression analyses were conducted to examine the relationships between variables. Results: P_max (r = 0.493, p = 0.006) and V₀ (r = 0.697, p < 0.001) showed moderate to strong correlations with critical velocity, whereas F₀ showed no significant association (r = 0.152, p = 0.422). Conversely, anaerobic capacity was strongly correlated with F₀ (r = 0.842, p < 0.001) but not with V₀ (p = 0.119). Regression models indicated that F₀ explained 71% of the variance in anaerobic capacity, while V₀ explained 48% of the variance in critical velocity. Conclusion: The findings demonstrated distinct contributions of neuromuscular qualities: speed and power-oriented parameters are associated with critical velocity, whereas maximal strength strongly associated with anaerobic capacity. Monitoring the upper-body load–velocity profile appears to be a relevant tool for individualizing dry-land training according to the aerobic and anaerobic demands of swimmers. Full article

In freshwater fish, group behavior is ecologically critical for daily activities such as predator avoidance. However, species with varying shoaling preferences exhibit divergent behavioral responses under different environmental conditions. This study investigated the behavioral responses of three shoaling species (Moenkhausia costae, Puntius tetrazona, and Myxocyprinus asiaticus) and three non-shoaling species (Trichogaster trichopterus, Micropterus salmoides, and Cichlasoma managuense) to simulated predation in either an open arena or a six-arm maze with shelter available. Our findings reveal that, in open water, shoaling species employ a dual strategy against predators: maintaining high group cohesion while increasing swimming speed and acceleration. This exploits the confusion effect to mitigate individual predation risk. In contrast, non-shoaling species do not engage in evasive maneuvers; instead, they adopt a cryptic strategy by minimizing activity and often freezing in place to avoid detection. In the six-arm maze, shoaling species consistently employed group coordination strategies, whereas non-shoaling species primarily relied on shelter concealment or reduced activity. Notably, shoaling species maintained high cohesion, synchronization, and activity levels across both open and complex habitats, using coordinated movement to facilitate collective escape. Together, our findings demonstrate that habitat complexity and social tendencies jointly determine how fishes trade off risk and safety. This work provides new insights into the adaptive evolution of social behavior in dynamic aquatic ecosystems. Full article

Objectives: The aim of this study was to analyze the utilization of the EO SwimBETTER^® (EoLab, Sydney, Autralia) device for measuring kinetic and kinematic variables during 50 m and 200 m freestyle trials. Methods: Ten swimmers (seven males and three females, 20 ± 3.5 years) participated. Each completed three sets of 50 m using EO SwimBETTER^® on non-consecutive days, with a 200 m test performed during the third session after recovery to complete the Critical Swim Speed Test (CSS-T). All tests were conducted at maximal intensity. Results: The results showed high reliability for both kinetic and kinematic parameters. Regarding validity, the EO SwimBETTER^® demonstrated strong agreement with the reference device in measuring stroke frequency (SF). In addition, higher mean force values were found in the 50 m compared with the 200 m trial (Δ% = 8.75%, p = 0.099), suggesting sensitivity of the device to different exertion demands. Conclusions: Based on these findings, the EO SwimBETTER^® appears to be a useful and promising tool for monitoring technical and performance-related variables in swimming, although further research is needed. Full article

The revalorization of animal by-products, such as porcine blood, is a key strategy for sustainable aquaculture and circular economy practices. This study aimed to fill the existing knowledge gap on the effects of spray-dried porcine blood hydrolysate (PBSH), assessing its potential as a functional feed ingredient for gilthead sea bream. Two practical diets were formulated: a control diet containing 5% blood meal, and a PBSH diet including 5% PBSH previously characterized in vitro. The results indicated that the PBSH diet promoted lower hepatosomatic index, a down-regulation of key hepatic lipogenic enzymes (scd1b, hl, lpl), and a better stress condition with lower circulating levels of glucose and cortisol and a reduction in aggressive attacks. Positive findings were also achieved in energy management, obtaining lower metabolic rates along with an enhanced swimming performance (20% increase in the critical speed) and a quicker weigh recovery after a fasting period. The PBSH diet also shaped the intestinal bacterial composition, determining a redistribution of abundant genera including Aureimonas and Halomonas. Ultimately, this study demonstrated that PBSH would act as a functional ingredient capable of enhancing fish energy management and resilience in the face of stressful events, exhibiting a transient transcriptional modulation, yet persistent physiological and welfare benefits. Full article

This study focuses on the impact of wastewater discharges from the Besòs treatment plant on the coastal water quality of Barcelona, particularly under adverse weather conditions. A simplified mathematical model was developed to predict, in real time, the concentration of bacterial indicators (Enterococci and E. coli) along nearby beaches. This model aims to quickly detect contamination events and trigger alerts to evacuate swimming areas before water quality tests are completed. The simulator uses meteorological data—such as wind direction and speed, rainfall intensity, and solar irradiance, among others—to anticipate pollution levels without requiring immediate water sampling. The model was tested against real-world scenarios and validated with historical meteorological and bacteriological data collected over six years. The results show that bacterial pollution occurs mainly during intense rainfall events combined with specific wind conditions, particularly when winds blow from the southeast (SE) or east–southeast (ESE) at moderate to high speeds. These wind patterns carry under-treated wastewater toward the coast. Conversely, winds from the north or northwest tend to disperse the contaminants offshore, posing little to no risk to swimmers. This study confirms that pollution events are relatively rare—about two per year—but pose significant health risks when they do occur. The simulator proved reliable, accurately predicting contamination episodes without producing false alarms. Minor variables such as water temperature or suspended solids showed limited influence, with wind and sunlight being the most critical factors. The model’s rapid response capability allows public authorities to take swift action, significantly reducing the risk to beachgoers. This system enhances current water quality monitoring by offering a predictive, cost-effective, and preventive tool for beach management in urban coastal environments. Full article

Swimming ability is an important means for shrimp to survive in a water environment. To investigate the effects of different body lengths (L₁: 6.5 ± 0.25 cm, L₂: 8.8 ± 0.16 cm, and L₃: 11.5 ± 0.28 cm) and different measurement methods on the measured critical swimming speeds (U_crit), this study used experimental ecology methods to determine the U_crit of three body length (BL) groups of whiteleg shrimp (Litopenaeus vannamei) at different time intervals (10, 20, 30, 40, and 50 min) and speed increments (1/2 BL s⁻¹, 3/4 BL s⁻¹, and BL s⁻¹) in a biological swimming channel. The results showed that the time interval and speed increment significantly affected the U_crit. In the small-body-length group (L₁), the U_crit of the shrimp decreased and then increased as the time interval increased, with no significant difference between time intervals or velocity increments. In the medium-body-length group (L₂), at the speed increment of 1/2 BL s⁻¹, the U_crit of the shrimp under the time interval < 40 min was significantly greater than that in the other treatment groups. At the speed increment of 1/2 BL s⁻¹, the U_crit of the shrimp decreased as the time interval increased. At the speed increment of 3/4 BL s⁻¹, the U_crit of the shrimp showed a trend of decreasing and then increasing with increasing time interval, and at a high-speed increment (BL s⁻¹), the time interval had no significant effect on U_crit. In the large-body-length group (L₃), at the speed increment of 1/2 BL s⁻¹, the U_crit of the shrimp under the time interval < 30 min was significantly higher than that in the other treatment groups. The effect of the time interval on U_crit was not significant at high-speed increments, and U_crit decreased with increasing time interval only at the speed increment of 1/2 BL s⁻¹. This study showed that, in the small-body-length group, the time increment has a more significant effect on the critical swimming speed, and, as the body length increases, both the time increment and velocity increment affect the critical swimming speed. When the time interval is 20 min and the speed increment is 1/2 BL s⁻¹, the measured U_crit is the closest to the appropriate value. Full article

Background: Estimating race times for open-water swimming based on pool swimming times could be useful for talent identification and training optimisation. We aimed to compare the swimming speeds of the world’s top and other swimmers in the 2023 Aquatics Championship men’s 10 km OWS race. Methods: Sixty-five swimmers were divided into four groups: G1 (1st–10th positions), G2 (11st–30th positions), G3 (31st–47th positions), and G4 (48th–65th positions). Swimming speed, stroke frequency (SF), and stroke length (SL) for each lap (laps 1–6) were recorded. Critical speed (CS) was calculated from each participant’s personal best times in the 400, 800, and 1500 m freestyle events in the pool. Swimming speed against CS was calculated (%CS). Results: The top performance group (G1) maintained their swimming speed from beginning (lap 1, 1.53 m/s) to end (lap 6, 1.50 m/s), at 92.7 ± 1.9% of CS, characterised by longer SL (1.26 m) and lower SF (72.86 rpm). G3 and G4 were unable to maintain their swimming speed, which decreased from G3: 97.64 ± 1.62% and G4: 96.10 ± 1.96% of CS at lap 1 to G3: 88.39 ± 3.78% and G4: 85.13 ± 5.04% at lap 6. This reduction in swimming speed is consistent with the increased reliance on anaerobic metabolism reported in previous studies under similar conditions. Conclusions: Race pacing for maintaining speeds of 92%CS throughout the race could be an important resilient index in open-water swimming. %CS might be a useful index for estimating the athletic performance level in open-water swimming. Full article