The neurotoxic effects of parabens have been previously proposed, however, the mechanisms driving its neurotoxicity remain largely uncharacterized. To better understand and identify the underlying mechanistic effects, methylparaben (MeP), the most common paraben produced, was exposed to embryonic zebrafish (Danio rerio) at environmentally relevant concentrations. Nontargeted and targeted metabolomics revealed that MeP primarily disrupted neurotransmitter-related metabolic pathways, leading to altered levels of gut microbiota associated neuroactive metabolites, suggesting impairment of neurobehavioral regulatory functions. Concurrently, MeP exposure significantly reduced locomotor activity, providing behavioral evidence for its neurotoxic effects. Comparisons between germ-free and conventionally reared zebrafish demonstrated that the absence of gut microbiota markedly alleviated MeP-induced neurotoxicity, as evidenced by weaker perturbations in neurotransmitter profiles and swimming behavior. Further, stable isotope-assisted high-resolution mass spectrometry revealed that gut microbes could reverse phase II detoxification through deconjugation reactions, regenerating MeP and enhancing systemic exposure. Overall, this study first reveals that MeP induces neurotoxicity through gut microbiota-mediated metabolic remodeling and biotransformation, providing new insights into the ecological risks of parabens.

Protocol for quantitative analysis of adult zebrafish swimming behavior using DeepLabCut.

Skeletogenesis is a tightly regulated process that is highly sensitive to abiotic factors and environmental change. Any skeletal abnormalities arising in early life can have lifelong consequences. Freshwater fish must cope with increased temperatures and declining pH, as well as with pollutants released into the environment by human activities. Our study aims to determine whether warming modulates the impacts of low pH and the environmental pollutant cadmium on zebrafish skeletal development. Zebrafish larvae were exposed to warming (31.5°C), acidification (pH 4.5) and cadmium (nominal concentration of 0.3 µmoll-1) in E3 medium from 0 till 7 days post fertilisation. Whole-body calcium content and mineralisation of craniofacial structures were reduced by low pH, cadmium, and a combination of both. Warming accelerates all physiological processes, including calcification, and was shown to partly mitigate the disruption of mineralisation induced by acidification. This attenuating effect of warming was found even after accounting for the thermal effects on development by comparing fish at the same developmental stage. In contrast, cadmium-induced disruption was not attenuated by warming. By comparing larval locomotor behaviour, it was shown that the effects of cadmium and acidification on swimming behaviour are dependent on environmental temperature, and occur mainly during the night. However, the combined effects of low pH and cadmium on swimming distance were not modulated by warming. In summary, we found that multiple stressors influence each other and impact calcium metabolism, bone development and swimming behaviour of zebrafish larvae. We found evidence for a mitigation of stressor effects in a warming context.

Swimming behavior of photobiomodulated Paramecium tetraurelia cells during NIR laser light irradiation

Swimming impairment caused by pharmaceuticals in native and invasive fishes: A comparison of fluoxetine effects in two poeciliid species.

The vertical slot fishway (VSF) has been widely installed to help fish pass hydropower dams, mitigating migration barriers from dam construction. Current research on VSF construction has not fully incorporated the fundamental principles of fish swimming kinematics and the quantification of trajectory characteristics, which is of great significance for optimizing existing VSFs and guiding future development. This study investigated the swimming behaviours, kinematics and trajectory characteristics of Procypris rabaudi (P.R.), Onychostoma sima (O.S.) and Squalidus argentatus (S.A.) in a VSF. Kinematics metrics included tail-beat frequency, angle, amplitude, midline kinematics and wavelength. The results demonstrated that the passage rate for the three fish species (8-10 cm body length) decreased as the outlet velocity increased. Analysis of trajectory hydraulic complexity revealed that swimming along side walls and baffles provided greater energy benefits. Furthermore, fish exhibited the lowest tail-beat frequency in recirculation zones, whereas the midline oscillation amplitude and wavelength progressively decreased from recirculation zones to the mainstream and slots. Long-term retention behaviours were also observed to adversely affect passage efficiency. This study thereby enhances understanding of fish swimming strategies and trajectory characteristics in VSFs.

Long-Term Monitoring of Swimming and Feeding Behaviors Related to Reproductive Cycles in Captive Loggerhead Turtles, Caretta caretta

The impact of flight restriction on the welfare of captive birds has been long debated. We conducted a study of individually identifiable Mandarin ducks (Aix galericulata) in an aviary at the Toledo Zoo and Aquarium to determine whether behavioral differences existed between flighted and flight-restricted individuals. We found that flight status only affected swimming and vocalization behavior, with flighted birds swimming more than flight-restricted birds and flight-restricted birds vocalizing more than flighted birds. Time of day and season exerted strong effects on behavior, with sex being less impactful. There were no differences in body weight, morbidity, or mortality between flighted and flight-restricted birds. Flight and flight attempt behaviors were rare. We conclude that flight restriction results in limited behavioral differences and no effects on health, and thus has minimal, if any, effect on behavioral and health indicators of welfare in this species in an aviary setting.

The swimming tilt angle of fish is one of the key factors influencing the estimation of target strength (TS). Therefore, understanding how TS varies with changes in swimming tilt angle is essential. This study employed the Kirchhoff-ray-mode (KRM) model to estimate TS and examine variations in the swimming tilt angle of sardines under flowing water conditions. Swimming tilt angles were measured at flow velocities of 30 and 50 cm/s. The KRM model was utilized to estimate TS for 17 sardine samples (total length: 13.0–24.6 cm) across four frequency bands (38, 70, 120, and 200 kHz). At a flow velocity of 30 cm/s, sardines swimming against the flow exhibited a mean swimming tilt angle of 4.0° ± 14.0°, with normalized mean TScm values of −64.7 dB at 38 kHz, −65.7 dB at 70 kHz, −66.4 dB at 120 kHz, and −66.9 dB at 200 kHz. At a flow velocity of 50 cm/s, sardines swimming against the flow showed a mean swimming tilt angle of −2.2° ± 10.1°, with normalized mean TScm values of −62.9 dB at 38 kHz, −63.7 dB at 70 kHz, −64.3 dB at 120 kHz, and −64.8 dB at 200 kHz. Considering the results of this study and the swimming behavior of sardines against the flow, the target strength of sardines swimming with the flow may be of less concern. Therefore, when conducting acoustic surveys, it is more efficient to account for flow velocity conditions rather than swimming direction.

Nanoplastics (NPs) with different hydrophobic properties are widely present in marine environments. However, the role of surface hydrophobicity in the bioaccumulation of NPs in the ecosystems is largely unknown. This study explores the role of surface hydrophobicity in trophic transfer of NPs along marine microalgae (Phaeodactylum tricornutum), mysids (Neomysis awatschensis), and fish (Sebastes schlegelii). For this, two types of Pd-doped polystyrene (PS) NPs (100 nm) were successfully synthesized, including hydrophobic PS1 NPs (octanol-water partition coefficients (Kow), 11.14) and hydrophilic PS2 NPs (Kow, 0.16). After 24-h dietary (algae-mysids) exposure (nominal concentrations, 1.0, 10.0 mg/L), hydrophobic PS1 NPs had higher accumulation in mysids than hydrophilic PS2 NPs due to much higher internalization of free PS1 NPs in seawater by mysids. Along NPs transfer (nominal concentrations, 1.0, 10.0 mg/L) from algae to mysids, and then fish, the contents of PS1 NPs in fish bodies (especially, gills, stomach, skin, blood, intestine, and liver) were also significantly higher than those of PS2 NPs. After dietary exposure, bioaccumulation factors (BAFs) of the two PS NPs in mysids and fish were 44-76 and 1-40 L/kg, respectively; and biomagnification factors (BMFs) along algae-mysids and algae-mysids-fish were 0.20-0.46 and 0.08-0.62, respectively. For PS1 NPs, both BAFs and BMFs were higher than those of PS2 NPs. Additionally, due to higher accumulation in fish brains, hydrophilic PS2 NPs exhibited more pronounced adverse effects on swimming and feeding behaviors of fish than hydrophobic PS1 NPs during dietary exposure. These findings highlight the importance of surface hydrophobicity on trophic transfer and the ecological risk of NPs in marine environments.

The migratory behaviour of Atlantic salmon kelts is poorly understood. Due to the Atlantic salmon's considerable socio-economic and ecological importance, their precipitous population abundance declines, and the population resilience potential of salmon kelts, addressing these knowledge gaps is important. In this study, directional swimming behaviours and position choice were quantified for the swimming trajectories of 48 acoustically tagged kelts in a regulated river. The kelts exhibited positive rheotaxis under high flow velocities, though their response to turbulence was more varied. The kelts exhibited clear preferences for moving between positions with similar hydraulic conditions and avoided moving to positions where the flow velocity or turbulence changed rapidly. The extent to which the kelts avoided moving to positions with rapid changes in hydraulic conditions varied by individual experience, individual body size, how active the individual was during daytime and how often an individual was detected near a conspecific. This study is the first to combine data on intrinsic individual characteristics with extrinsic hydraulic factors to conduct a detailed analysis of kelt behaviour during migration in a regulated river. By examining these behaviours across different hydraulic conditions, our findings bear important implications for both hydropower development and river management practices.

A unique type of locomotion was recently discovered that honey bees (Apis mellifera L.) could propel their own body on water surface by keeping their upper wing surface dry while moving their wings. However, it was not clear whether such locomotive behavior was ecologically meaningful. Here we show that honey bees preferred a dark region (skototaxis) while hydrofoiling on the water surface in trying to reach the edge. However, this skototaxis was disrupted by a neonicotinoid insecticide thiamethoxam, via reducing the honey bees' motor control. Finally, we show that mason bees (Osmia excavata) also displayed skototaxis, showing a significantly stronger preference for dark than honey bees. The female mason bees exhibited higher efficiency than males in swimming, as indicated by their shorter durations and distances. These findings suggest that swimming behavior in bees evolved before sociality and serves important adaptive and ecological functions. However, environmental pollution from excessive pesticide use may negatively impact this behavior.

Ploidy and neuron size impact nervous system development and function in Xenopus.

Oxidative and nitrosative stress are central mechanisms in the pathogenesis of neurodegenerative diseases, where excessive production of reactive oxygen and nitrogen species (ROS/RNS) leads to mitochondrial dysfunction, membrane damage, and neuronal death. In this study, we established and compared short-term (2 h) and long-term (20 h) exposure paradigms to sodium nitroprusside (SNP), used as a xenobiotic nitric oxide donor, in two neuronal cell lines (mHippoE-18 and PC12) and zebrafish larvae, aiming to provide a preclinical framework for neurodegenerative drug discovery. In vitro, SNP exposure caused concentration-dependent reductions in viability and alterations in oxidative balance, with mHippoE-18 cells exhibiting higher susceptibility than PC12 cells. In the short-term exposure paradigm, cytotoxicity was primarily associated with membrane disruption at higher concentrations, whereas oxidative stress contributed more strongly at intermediate doses. In the long-term exposure, mHippoE-18 cells showed strong integrated correlations between ROS, LDH release, and viability loss, highlighting their increased vulnerability to nitrosative stress. In zebrafish, SNP exposure impaired metabolic activity and swimming behavior in both paradigms. Long-term exposure led to consistent dose-dependent increases in ROS, accompanied by locomotor deficits tightly linked to energy metabolism. Overall, the higher sensitivity of mHippoE-18 cells compared with PC12 cells, together with the dose-dependent metabolic and behavioral impairments observed in zebrafish, indicates that cellular responses partially mirror in vivo outcomes. This integrative approach underscores the value of combining neuronal cell lines with zebrafish larvae to capture complementary aspects of SNP-induced neurotoxicity and to strengthen preclinical evaluation of candidate compounds with protective or therapeutic potential. These findings support the use of SNP as a xenobiotic model to probe nitrosative stress-driven neurotoxicity across cellular and organismal systems.

Differential effects of gallium and indium addition on metal bioavailability and toxicity in paddy soils: Insights from a soil-water-fish exposure system.

Social interactions in medaka fish depend on discrete kinematic states of swimming behavior.

Dual-pathway synergistic catalytic mechanism based on FeN3P-CoN3P active sites: A three-channel colorimetric sensing array for efficient detection and green performance evaluation of five organophosphorus pesticides in complex matrices.

What are the toxicological effects of mixing nanoplastics with a nanopesticide on Daphnia magna and Aliivibrio fischeri?

BiFeO3/graphitic-carbon/PVDF composite with an electrical percolation network to enhance ciprofloxacin removal by photoelectrocatalytic ozonation.

Benthic habitat influences sea scallop distributions and swimming behavior based on underwater imagery and machine learning