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Chub mackerel Scomber japonicus is a migratory fish widely distributed around Japan, and is an important fishery resource. However, target strength (TS) measurements of chub mackerel are limited, and the relationship between TS and fork length has not been fully clarified, despite its importance for the estimation of chub mackerel abundance. In this study, the TS–fork length (FL) relationship in chub mackerel was evaluated under realistic conditions. TSmean and TSmax tended to increase with fork length at both 38 and 120 kHz, and TS histograms were bimodal for most individuals. In the TSmean–FL relationship, when the coefficient a was fixed at 20 (the standard for fish with swim bladders), TScm (standardized by the square of the fork length) was −67.9 dB (r2 = 0.70) at 38 kHz and −69.2 dB (r2 = 0.45) at 120 kHz. Additionally, the swimming angle had a peak of around 0° with a mean of −1.23°, and the mean swimming speed was 0.16 FL/s with a standard deviation of 0.07 FL/s. TS reached a maximum between −20° and 0° and then decreased drastically as the swimming angle increased or decreased. Our results have practical implications for the management of chub mackerel.

The changes in water flow caused by hydropower projects and river diversions have had a profound impact on aquatic ecosystems, especially due to artificial structures such as dams and bridge piers. This study investigates the swimming behavior differences between single and dual fish in the wake region behind a D-shaped obstacle, using Percocypris pingi as the experimental species. The results show that single fish efficiently utilize vortex energy through the Kármán gait, improving swimming efficiency, while the dual-fish group failed to maintain a stable Kármán gait, resulting in irregular swimming trajectories. However, the dual-fish group optimized wake utilization by maintaining a fore–aft linear alignment, improving swimming efficiency and resisting vortices. The conclusion indicates that mutual interference in group swimming affects swimming efficiency, with fish adjusting their swimming patterns to adapt to complex hydrodynamic conditions. By altering swimming formations, fish schools can adapt to the flow environment, offering new insights into the swimming behavior of fish and providing theoretical support for ecological conservation and hydropower project design.

Cellular membrane is a key component for maintaining cell shape and integrity. The classical membrane structure and function by Singer and Nicolson groundbreaking model has depicted the membrane as a homogeneous fluid structure. This view has changed by the discovery of discrete domains containing different lipid compositions, called lipid rafts, which play a key role in signal transduction in eukaryotic cells. In the past few years, lipid raft-like structures have been found in bacteria also, constituted by cardiolipin and other modified lipids, perhaps involved in generating a specific site for protein clustering. Here, we report the analysis of a protein termed YqiK from Escherichia coli, a prohibitin homolog that has been implicated in stress sensing by the formation of membrane-associated microdomains. The E. coli yqiK-deficient mutant strain showed an enhanced swimming behavior and was resistant to ampicillin but its response to other stressing conditions was similar to that of the wild-type strain. The abnormal swimming behavior is reversed when the protein is expressed in trans from a plasmid. Also, we demonstrate that YqiK is not redundant with QmcA, another flotillin homolog found in E. coli. Our results, along with the data available in the literature, suggest that YqiK may be involved in the formation of discrete membrane-associated signaling complexes that regulate and agglomerate signaling proteins to generate cell response to chemotaxis.

Fishes exhibit an astounding diversity of locomotor behaviors from classic swimming with their body and fins to jumping, flying, walking, and burrowing. Fishes that use their body and caudal fin (BCF) during undulatory swimming have been traditionally divided into modes based on the length of the propulsive body wave and the ratio of head:tail oscillation amplitude: anguilliform, subcarangiform, carangiform, and thunniform. This classification was first proposed based on key morphological traits, such as body stiffness and elongation, to group fishes based on their expected swimming mechanics. Here, we present a comparative study of 44 diverse species quantifying the kinematics and morphology of BCF-swimming fishes. Our results reveal that most species we studied share similar oscillation amplitude during steady locomotion that can be modeled using a second-degree order polynomial. The length of the propulsive body wave was shorter for species classified as anguilliform and longer for those classified as thunniform, although substantial variability existed both within and among species. Moreover, there was no decrease in head:tail amplitude from the anguilliform to thunniform mode of locomotion as we expected from the traditional classification. While the expected swimming modes correlated with morphological traits, they did not accurately represent the kinematics of BCF locomotion. These results indicate that even fish species differing as substantially in morphology as tuna and eel exhibit statistically similar two-dimensional midline kinematics and point toward unifying locomotor hydrodynamic mechanisms that can serve as the basis for understanding aquatic locomotion and controlling biomimetic aquatic robots.

Ivermectin (IVM) is a broad acting antihelmintic used in various veterinary pharmaceuticals. It has been shown that IVM enters the aquatic compartment and adversely affects organisms including fish. This study is based on the hypothesis that long term exposure to IVM affects fish and thus, the main objective was to assess the chronic effects of 0.25 and 25 µg IVM/L to zebrafish using multiple endpoints representative of several levels of biological organization: weight, behaviour (swimming and feeding) and subcellular markers including biomarkers for oestrogenicity (vitellogenin-VTG), oxidative stress (catalase-CAT and glutathione-S-transferase-GST) and neurotransmission (cholinesterase-ChE). Concentrations as low as 0.25 µg IVM/L disrupted the swimming behaviour, causing fish to spend more time at the bottom of aquaria. Such reduction of the swimming performance affected the feeding ability which is likely responsible for the weight loss. The effects on weight were gender differentiated, being more pronounced in males (0.25 µg IVM/L) than in females (25 µg IVM/L). Fish exposed to 25 µg/L exhibited darker coloration and mild curvature of the spine. No effects on VTG and AChE were observed, but a reduction on CAT and GST levels was observed in fish exposed to 25 µg IVM/L, although these alterations probably only reflect the general condition of the fish which was significantly compromised at this concentration. Despite that predicted environmental concentrations of IVM are below 0.25 µg/L, the behavioural effects may be translated into important ecological impacts, e.g. at predator–prey interactions where fish competitive advantage can be decreased. Future work should address the link between behaviour disruption and population fitness. The current study was based on a one experiment and multiple endpoint (anchored) approach, allowing the results to be integrated and linked towards a mechanistic understanding.

Procaine penicillin (PP) is a β-lactam antibiotic widely used in human and veterinary medicine. Although PP is detected in surface water, little is known on its effects on aquatic invertebrates. Our aim was to determine the influence of PP on swimming behaviour (track density, swimming speed, turning angle, hopping frequency) and physiological activity (oxygen consumption, heart rate, thoracic limb movement) of a freshwater invertebrate Daphnia magna exposed to PP at concentrations of 11.79 mg/L, 117.9 mg/L and 1179 mg/L for 2 h and 24 h. The results showed no mortality; however, reduction of swimming activity manifested by the decreased track density, swimming speed and turning angle noted in Daphnia exposed to all the concentrations of PP. Increase of oxygen consumption was observed after 2-h exposure; however, decrease of this parameter was found after 24 h. PP also reduced heart rate and thoracic limb movement in a concentration-dependent manner. The results suggest that the antibiotic should not induce mortality; however, it may affect swimming behaviour and physiological parameters of Daphnia magna particularly inhabiting aquaculture facilities with intensive antibiotic treatment. On the basis of the present results, we also suggest higher sensitivity of behavioural and physiological parameters of cladocerans than the commonly used endpoints: mortality or immobilisation and their possible application as a part of early warning systems in monitoring of surface water toxicity.

Selective serotonin re-uptake inhibitors are pharmaceuticals used to treat a range of psychological disorders. They are frequently found in surface waters in populated areas. In recent years, they have been shown to affect the behaviour of various aquatic organisms in a way that can have ecological effects. In this study, we exposed zebrafish of both sexes to nominally 0.00, 0.15 and 1.50 µg L−1 Escitalopram in flow-through tanks for three weeks. Subsequently, ten swimming behaviour parameters were quantified using high-resolution video tracking. There were noticeable gender differences in the behaviour responses to Escitalopram. Female fish exposed to 1.50 µg L−1 Escitalopram had a lower maximum swimming velocity, stopped less often and exhibited increased boldness (reduced thigmotaxis) compared to controls. Male fish exposed to 1.50 µg L−1 had a lower maximum swimming velocity compared to control fish. At the end of exposures, both length and weight of the females exposed to 1.50 µg L−1 Escitalopram were significantly less than the group of control fish. In addition, males exposed to 1.50 µg L−1 Escitalopram were significantly shorter than control fish. The behaviour, weight and body length of the fish exposed to nominally 0.15 µg L−1 was not significantly different from control fish in either sex. The results of this study demonstrate that Escitalopram can affect subtle but ecologically important aspects of fish behaviour and lends further credibility to the assumption that Escitalopram is an environmentally active pharmaceutical.

The insecticide fipronil, one of the main pesticides used in Brazil, is often detected in natural aquatic environments, and causes neuronal hyperexcitation by inhibiting GABAergic neurotransmission, leading to putative alterations in behaviour and development. This work sought to analyse the toxicity of formulated Regent® 800WG (80% fipronil) on development (fish embryo toxicity test, FET), morphology, and swimming behaviour of larvae and adults of zebrafish (Danio rerio). FET was performed following OECD236 guidelines at concentrations ranging from 0.002 to 1600 μg.L−1 of formulated Regent® 800WG. Adults were exposed to 0.2, 2 and 20 μg.L−1 of the product for 24 and 96 h, and were submitted to the light-dark, novel tank and swimming endurance tests No lethal parameters were observed in larvae, but in concentrations above 400 µg.L−1, there was shortening of the body axis and decreased swimming behavior. In adults, exposure to the pesticide did not lead to changes in free swimming parameters. However, a marked decrease of swimming endurance was observed at all experimental treatments, although probably not in consequence of energetic depletion, since baseline blood glucose levels and condition factor were similar at all conditions. Furthermore, zebrafish adults did not show their natural preference for the dark environment. The pesticide likely has anxiolytic effects on zebrafish, as well as a compromising effect on locomotor control, illustrating that behavioural changes, which could affect activities on the natural environment, such as escape and predation, may occur even in environmentally relevant concentrations of this pollutant.

A major trend in marine aquaculture is to move production to more exposed sites with occasionally rough ocean current events. However, it is unclear whether fish will thrive in these extreme environments, since thorough descriptions of ambient current conditions with regards to fish welfare is lacking. In the present study, ocean current data were collected using acoustic Doppler current profilers at 5 exposed sites along the Norwegian coast over minimum periods of 5 mo. To evaluate welfare risks, current data was compared to known limits of swimming capabilities, such as onset of behavioural changes and critical swimming speeds (Ucrit), of Atlantic salmon Salmo salar and lumpfish Cyclopterus lumpus. Specifically, at each site, current speeds were classified into 6 categories based on expected impact on swimming behaviours of Atlantic salmon, and duration of currents within each category were inspected using a homogeneous and non-homogeneous criterion for the water column. Current speeds were then compared with projected Ucrit at relevant temperatures and fish sizes of Atlantic salmon and lumpfish. Furthermore, a detailed characterization of extreme events at the most exposed site was performed. Of the 5 locations, only 1 exceeded the Ucrit of Atlantic salmon, while all sites featured currents above Ucrit of lumpfish for up to 33 h at a time. These results suggest that responsible Atlantic salmon farming is possible at sites considered exposed, while lumpfish should be restricted to more sheltered environments. The presented method can be applied for other aquaculture fish species if adequate data are available

It is critical for bacteria to recognize surface contact and initiate physiological changes required for surface-associated lifestyles. Ubiquitous microbial appendages called pili are involved in sensing surfaces and facilitating downstream behaviors, but the mechanism by which pili mediate surface sensing has been unclear. We visualized Caulobacter crescentus pili undergoing dynamic cycles of extension and retraction. Within seconds of surface contact, these cycles ceased, which coincided with synthesis of the adhesive holdfast required for attachment. Physically blocking pili imposed resistance to pilus retraction, which was sufficient to stimulate holdfast synthesis without surface contact. Thus, to sense surfaces, bacteria use the resistance on retracting, surface-bound pili that occurs upon surface contact.