Swimming Behavior Research Articles

Interactive effects between water temperature, microparticle compositions, and fiber types on the marine keystone species Americamysis bahia

Recently, there has been an increasing emphasis on examining the ecotoxicological effects of anthropogenic microparticles (MPs), especially microplastic particles, and related issues. Nevertheless, a notable deficiency exists in our understanding of the consequences on marine organisms, specifically in relation to microfibers and the combined influence of MPs and temperature.In this investigation, mysid shrimp (Americamysis bahia), an important species and prey item in estuarine and marine food webs, were subjected to four separate experimental trials involving fibers (cotton, nylon, polyester, hemp; 3 particles/ml; approximately 200 μm in length) or fragments (low-density Polyethylene: LDPE, polylactic acid: PLA, and their leachates; 5, 50, 200, 500 particles/ml; 1–20 μm). To consider the effects in the context of climate change, three different temperatures (22, 25, and 28 °C) were examined. Organismal growth and swimming behavior were measured following exposure to fragments and microfibers, and reactive oxygen species and particle uptake were investigated after microfiber exposure. To simulate the physical characteristics of MP exposure, such as microfibers obstructing the gills, we also assessed the post-fiber-exposure swimming behavior in an oxygen-depleted environment.Data revealed negligible fragment, but fiber exposure effects on growth. PLA leachate triggered higher activity at 25 °C and 28 °C; LDPE exposures led to decreased activity at 28 °C. Cotton exposures led to fewer behavioral differences compared to controls than other fiber types. The exposure to hemp fibers resulted in significant ROS increases at 28 °C. Microfibers were predominantly located within the gastric and upper gastrointestinal tract, suggesting extended periods of residence and the potential for obstructive phenomena over the longer term. The combination of increasing water temperatures, microplastic influx, and oxidative stress has the potential to pose risks to all components of marine and aquatic food webs.

Enhanced neurotoxic effect of PCB-153 when co-exposed with polystyrene nanoplastics in zebrafish larvae

Nanoplastics (NPs) and persistent organic pollutants such as polychlorinated biphenyls (PCBs) are ubiquitous aquatic pollutants. The coexistence of these pollutants in the environment emphasises the need to study their combined toxicity. NPs can cross biological membranes and act as vectors for other pollutants, whereas PCBs are known for their ability to bioaccumulate and biomagnify. The present work aimed to study the combined toxicity of polystyrene NPs and PCB-153 using physiological (development, heart rate, respiration), behavioural (swimming behaviour) and molecular (transcriptome) endpoints in zebrafish larvae. The results show that exposure to NPs, PCB and their mixture significantly affected the development and respiration in zebrafish larvae. Larvae co-exposed to NPs and PCB exhibited significant hyperlocomotion, whereas no such effect was observed after exposure to NPs or PCB alone. The transcriptomic results revealed that NPs exposure significantly affected several pathways associated with DNA compaction and nucleosome assembly, whereas PCB exposure significantly affected critical neurogenic pathways. In contrast, co-exposure to NPs and PCB generated multi-faceted toxicity and suppressed neurobehavioural, immune-related and detoxification pathways. The study highlights the complex interplay between NPs and PCBs, and documents how the two toxicants in combination give a stronger effect than the single toxicants alone. Understanding the mixture toxicity of these two pollutants is important to assess the environmental risks and developing effective management strategies, ultimately safeguarding ecosystems and human health.

Plant-Derived Products Selectively Suppress Growth of the Harmful Alga Prymnesium parvum

Prymnesium parvum is a harmful alga found in brackish waters worldwide whose toxins can be lethal to aquatic organisms. Established field methods to control blooms of this species, however, are unavailable. Earlier studies showed that various extracts of giant reed (Arundo donax) can suppress P. parvum growth and that ellipticine, an allelochemical present in giant reed, is a potent algicide against this species. The unintended effects of giant reed products on nontarget organisms, however, are not fully understood. This study determined the effects of giant reed leachate (aqueous extract of dried chips) and ellipticine on growth of P. parvum and the green microalga Chlorella sorokiniana; survival and reproduction of the planktonic crustacean Daphnia pulex; and hatching success, larval survival, and larval swimming behavior of the teleost fish Danio rerio. Leachate made with 3 g chips L−1 was lethally toxic to P. parvum and D. pulex, stimulated C. sorokiniana growth, and impaired D. rerio behavior. Leachate at 1 g L−1 fully suppressed P. parvum growth, had moderate effects on D. pulex reproductive output, and had no effects on D. rerio. Ellipticine at 0.01 mg L−1 irreversibly inhibited P. parvum growth, acutely but reversibly inhibited C. sorokiniana growth, slightly delayed D. pulex reproduction, and had no effects on D. rerio. These observations suggest that when applied at appropriate concentrations, natural products derived from giant reed can be used as tools to specifically control P. parvum growth with minimal effects on nontarget species.

Sensory cells in tunicates: insights into mechanoreceptor evolution.

Tunicates, the sister group of vertebrates, offer a unique perspective for evolutionary developmental studies (Evo-Devo) due to their simple anatomical organization. Moreover, the separation of tunicates from vertebrates predated the vertebrate-specific genome duplications. As adults, they include both sessile and pelagic species, with very limited mobility requirements related mainly to water filtration. In sessile species, larvae exhibit simple swimming behaviors that are required for the selection of a suitable substrate on which to metamorphose. Despite their apparent simplicity, tunicates display a variety of mechanoreceptor structures involving both primary and secondary sensory cells (i.e., coronal sensory cells). This review encapsulates two decades of research on tunicate mechanoreception focusing on the coronal organ's sensory cells as prime candidates for understanding the evolution of vertebrate hair cells of the inner ear and the lateral line organ. The review spans anatomical, cellular and molecular levels emphasizing both similarity and differences between tunicate and vertebrate mechanoreception strategies. The evolutionary significance of mechanoreception is discussed within the broader context of Evo-Devo studies, shedding light on the intricate pathways that have shaped the sensory system in chordates.

The effect of supplementation of Lactococcus lactis strain as probiotic on the growth and survival of Litopenaeus vannamei

Acute Hepatopancreatic Necrosis Disease (AHPND) or Early Mortality Syndrome (EMS) is a bacterial disease in shrimps caused by pathogen Vibrio parahaemolyticus. It has culminated in huge loss in global shrimp production due to mass mortality. A probiotic strain Lactococcus lactis strain FA1 was recently isolated from shark intestine, showing inhibition towards the growth of the pathogen. Due to inhibitory potential, the effect of probiotics strain on growth performance of shrimp infected with V. parahaemolyticus was evaluated. The probiotic strain was incorporated into feed for juvenile shrimps Litopanaeus vannamei for 3 weeks before which they were then challenged with pathogen Vibro parahaemolyticus. The study compares 4 shrimp groups: Control (Without any treatment); Group A (Probiotic treated, uninfected); Group B (Probiotic treated, infected) and Group C (No probiotic, infected). The survival and growth performance (weight and length gain) of shrimps were evaluated in the following 30 days. Statistical analyses (ANOVA; Post Hoc Tukey) were used to compare between shrimp groups. In general, infected shrimp demonstrated some of the key symptoms of AHPND (pale or white hepatopancreas), transparent body and erratic swimming behaviour. The supplementation of probiotics resulted in an improved survivability (65±1%) compared to infected shrimp (45±1%). The probiotic treated shrimp group showed to have better % body weight gain, in which weight gain between group B (treated/infected) and group C (untreated/infected) were significantly different (at P=0.046); and so, to group A (treated/uninfected) when compared with group C (P=0.047). There is however no significant difference in % length gain between the groups. Meanwhile, some of the infected shrimps were able to show recovery from the infection. Pre-infection probiotic treatment showed better performance compared to post-infection probiotic treatment. This indicated that the strain Lactococcus lactis is highly suitable for use as the future probiotic in shrimp aquaculture.

Adaptive responses of feeding and swimming behaviors in black rockfish, Sebastes schlegelii, under starvation at juvenile and young stages

Starvation is a ubiquitous stress that many fish species have to cope with. To investigate the behavioral responses under this pressure in the fry stage, black rockfish (Sebastes schlegelii) at juvenile (29 days of age, 15.2 ± 1.0 mm in total length) and young (51 days of age, 40.3 ± 1.2 mm in total length) stages were starved for 12 and 21 days, respectively. During these two periods of starvation, the starved and routinely fed individuals (serving as the control group) were sampled to be analyzed the variations in growth, survival, feeding activity, swimming ability (cruise and burst), and diet transition process. The results indicated that juveniles were more sensitive to hunger, and the point of no return (PNR) was approximately 5.5 days (19 ℃ in water temperature). In contrast, the young fish had a significantly higher tolerance to starvation because the survival rate after 21 days of starvation was still higher than 99% (20 ℃). The total length and body weight of juveniles and young fish showed different degrees of negative growth. After the starvation for 1 day, the juveniles’ feeding activity on shrimps increased significantly (p < 0.05), while their cruising speed and time changed insignificantly. Similar results were observed in young fish been starved for 1–3 days. With the prolongation of starvation, however, both the feeding and cruising activities of black rockfish became significantly lower than those of the control groups (p < 0.05). The burst swimming ability did not seem to be affected by starvation time. Although the short-term starvation would not increase the young fish’s predation on shrimp, it might be serviceable for improving their feeding vitality. These behavioral results would help us understand the adaptive processes and response mechanisms of fish under starvation.

Phenotype‐dependent downstream dispersal under ordinary flow conditions in juvenile white‐spotted char

AbstractAnimal dispersal is often phenotype‐dependent and can exert evolutionary pressures on populations in which it occurs. The evolutionary pressure arising from phenotype‐dependent dispersal is called spatial sorting. We examined the evolutionary pressure arising from spatial sorting (sorting pressure) caused by downstream dispersal in juvenile white‐spotted char Salvelinus leucomaenis under ordinary flow conditions. We conducted outdoor experiments using an artificial channel with 10 steps to investigate the relationship between phenotypic characteristics and the occurrence or distance of downstream dispersal during five daytime hours. Six experiments were conducted using young‐of‐the‐year juveniles collected early in the morning of each experimental day. We focused on two phenotypes, fork length (body size) and station‐holding (SH) behavior, where juveniles remain sedentary on the substrate. Juveniles were assigned to the “SH group” if they exhibited SH behavior for more than 10 s during a 540‐s observation period, and to the “swimming group” if they exhibited SH behavior for less than 10 s. Juveniles in the swimming group had a higher occurrence of downstream dispersal than in the SH group. In addition, large juveniles in the SH group and small juveniles in the swimming group tended to show long dispersal distances. These results suggest an effective sorting pressure against juveniles with active swimming behavior. This sorting pressure may accumulate in isolated char populations located above a tall migration barrier and contribute to the creation and maintenance of the reported interpopulation variation in SH behavior.

Swimming behavior as a potential metric to detect satiation levels of European seabass in marine cages

Aquaculture is anticipated to contribute to two-thirds of the world’s fish consumption by 2030, emphasizing the need for innovative methods to optimize practices for economic viability, social responsibility, and environmental sustainability. Feeding practices play a pivotal role in aquaculture success and the feeding requirements are dynamic, influenced by factors like fish size, environmental conditions, and health status necessitating ongoing improvements in feeding practices. This study addresses a critical gap in feeding control systems in sea cages. It introduces a continuous, real-time monitoring system for analyzing the feeding behavior of European seabass, employing advanced AI models (YOLO and DEEPSORT) and computer vision techniques. The investigation focuses on key parameters, including speed and the newly defined feeding behavior index (FBI), to evaluate swimming responses under varying feeding scenarios exploring meal frequency, feeding time, and feeding quantity. The findings reveal a sensitivity of fish speed and the feeding behavior index (FBI) to different feeding scenarios, elucidating distinct behavioral patterns in response to varying frequencies, times, and quantities of feeding, such as increased activity in the morning relative to later times and the emergence of asymmetric activity patterns when fish are underfed or overfed. Notably, this study is one of the few in the field, presenting the development of a continuous, real-time monitoring system for feeding control in sea cages. Simultaneously, it explores reference curves and threshold values to enhance the overall efficacy of feeding control measures.

Dimensionality of locomotor behaviors in developing C. elegans.

Adult animals display robust locomotion, yet the timeline and mechanisms of how juvenile animals acquire coordinated movements and how these movements evolve during development are not well understood. Recent advances in quantitative behavioral analyses have paved the way for investigating complex natural behaviors like locomotion. In this study, we tracked the swimming and crawling behaviors of the nematode Caenorhabditis elegans from postembryonic development through to adulthood. Our principal component analyses revealed that adult C. elegans swimming is low dimensional, suggesting that a small number of distinct postures, or eigenworms, account for most of the variance in the body shapes that constitute swimming behavior. Additionally, we found that crawling behavior in adult C. elegans is similarly low dimensional, corroborating previous studies. Further, our analysis revealed that swimming and crawling are distinguishable within the eigenworm space. Remarkably, young L1 larvae are capable of producing the postural shapes for swimming and crawling seen in adults, despite frequent instances of uncoordinated body movements. In contrast, late L1 larvae exhibit robust coordination of locomotion, while many neurons crucial for adult locomotion are still under development. In conclusion, this study establishes a comprehensive quantitative behavioral framework for understanding the neural basis of locomotor development, including distinct gaits such as swimming and crawling in C. elegans.

Study on the influence of queue modes on the hydrodynamic performance of fish schooling swimming

In this study, computational fluid dynamics (CFD) models were used to investigate how different queue patterns affect the hydrodynamic performance of fish schooling. Various queue modes—such as tandem, parallel, and rectangular—were simulated to analyze fish swimming behaviors and hydrodynamics. Results indicated that both the queue pattern and fish spacing influence collective fish swimming. In tandem queues, fish exhibited improved speeds, with leading fish showing a 39.3% increase in cruising speed compared to single fish at dy =0.3L. However, larger spacing led to decreased fish speeds, with two fish at dy =1.2L nearing the speed of a single fish (0.12 and 0.02L/s differences). In parallel queues, fish swimming speed was lower than that of a single fish, especially when dx =1.5D, with inner fish cruising at 49.9% of a single fish's speed. Yet, increased spacing at dx =4D saw speeds nearing equality (0.01L/s differences), suggesting reduced queue impact. Rectangular queues showcased varying fish speeds, notably with outer rear fish displaying superior propulsion. As spacing increased, all fish tended toward a single fish's speed. Analyses of single fish, including acceleration and wake interactions, revealed collective movement utilizing vortices to generate thrust and create low-pressure zones, thus enhancing hydrodynamics. This research sheds light on how queue modes and spacing affect fish collective behavior and swimming dynamics, offering insights into collective dynamics and biological behaviors.

A free and user-friendly software protocol for the quantification of microfauna swimming behavior.

Characterizing swimming behavior can provide a holistic assessment of the health, physiologyand ecology of microfaunal species when done in conjunction with measuring other biological parameters. However, tracking and quantifying microfauna swimming behavior using existing automated tools is often difficult due to the animals' small size or transparency, or because of the high cost, expertise, or labor needed for the analysis. To address these issues, we created a cost-effective, user-friendly protocol for behavior analysis that employs the free software packages HitFilm and ToxTrac along with the R package 'trajr'and used the method to quantify the behavior of rotifers. This protocol can be used for other microfaunal species for which investigators may face similar issues in obtaining measurements of swimming behavior.

Swimming behaviour of Atlantic salmon kelts migrating past a hydropower plant dam: Effects of hydraulics and dam operations

Hydropower plants commonly impede the downstream migration of Atlantic salmon (Salmo salar) kelts. Thus, understanding the effects of hydraulic conditions on kelt behaviour and passage performance at dams is crucial for developing effective mitigation measures. In this study, we investigated the influence of hydraulic conditions on kelt passage performance and swimming behaviour at a Norwegian hydropower plant. We combined biological data from 48 kelts collected via acoustic telemetry with hydraulic data modelled using computational fluid dynamics. We assessed kelt passage performance using metrics such as time-to-pass, total number of detections, and total number of detections per day. Additionally, we analysed swimming depths and speeds in relation to the hydraulic conditions created by different dam operating conditions. We found that the dam operation schedule impacted the kelts' ability to find a route past the dam. Though kelts could have passed the dam throughout the study period via a submerged pipe at the dam (which had seemingly sufficient discharge for the kelts to find), 98 % of the kelts instead waited for a spill gate to open partway through the study period. The swimming depth analysis indicated diel variation, with kelts swimming nearer to the water surface during the night. We found that swimming speed increased with increasing kelt body length, particularly under high turbulence kinetic energy and during the day. Furthermore, kelts swam faster as water velocity increased, but slowed down again as turbulence intensity increased. Our findings reveal the effects of hydraulic conditions and dam operations on the migration behaviour of Atlantic salmon kelts. This provides valuable insights for developing strategies to optimise dam operations and improve fish passage performance, including the need to spill enough water to increase passage success and will contribute to sustainable management of Atlantic salmon populations in regulated rivers.

Optimization of Laser-Based Method to Conduct Skin Ablation in Zebrafish and Development of Deep Learning-Based Method for Skin Wound-Size Measurement

Skin plays an important role as a defense mechanism against environmental pathogens in organisms such as humans or animals. Once the skin integrity is disturbed by a wound, pathogens can penetrate easily into a deeper part of the body to induce disease. By this means, it is important for the skin to regenerate quickly upon injury to regain its protective barrier function. Traditionally, scientists use rodents or mammals as experimental animals to study skin wound healing. However, due to concerns about animal welfare and increasing costs of laboratory animals, such as rodents, scientists have considered alternative methods of implementing replace, reduce, and refine (3Rs) in experimentation. Moreover, several previous studies on skin wound healing in fish used relatively expensive medical-grade lasers with a low calculation efficiency of the wound area, which led to human judgment errors. Thus, this study aimed to develop a new alternative model for skin wound healing by utilizing zebrafish together with a new rapid and efficient method as an alternative in investigating skin wound healing. First, in order to fulfill the 3Rs concept, the pain in the tested zebrafish was evaluated by using a 3D locomotion assay. Afterward, the obtained behavior data were analyzed using the Kruskal–Wallis test, followed by Dunn’s multiple comparisons tests; later, 3 watts was chosen as the power for the laser, since the wound caused by the laser at this power did not significantly alter zebrafish swimming behaviors. Furthermore, we also optimized the experimental conditions of zebrafish skin wound healing using a laser engraving machine, which can create skin wounds with a high reproducibility in size and depth. The wound closure of the tested zebrafish was then analyzed by using a two-way ANOVA, and presented in 25%, 50%, and 75% of wound-closure percentages. After imparting wounds to the skin of the zebrafish, wound images were collected and used for deep-learning training by convolutional neural networks (CNNs), either the Mask-RCNN or U-Net, so that the computer could calculate the area of the skin wounds in an automatic manner. Using ImageJ manual counting as a gold standard, we found that the U-Net performance was better than the Mask RCNN for zebrafish skin wound judgment. For proof-of-concept validation, a U-Net trained model was applied to study and determine the effect of different temperatures and the administration of antioxidants on the skin wound-healing kinetics. Results showed a significant positive correlation between the speed of wound closure and the exposure to different temperatures and administration of antioxidants. Taken together, the laser-based skin ablation and deep learning-based wound-size measurement methods reported in this study provide a faster, reliable, and reduced suffering protocol to conduct skin wound healing in zebrafish for the first time.

Swimming behavior indicates stress and adaptations to exercise.

Introduction: Behaviors of swimming rodents are not uniform, exhibiting large variations, which may underlie the individual differences in swimming exercise-induced benefits. The study aimed to monitor individualized swimming behavior and evaluate its biological significance. Methods: A swimming tank which can monitor individualized rodent swimming behavior during exercise was established. A total of 45 mice were subjected to swimming training for 1 month (1h per day) and the swimming behaviors of each mouse were recorded. Results: The swimming behaviors of mice displayed considerable variations in aspects of distance, velocity, and area preference. For example, nearly one-third of mice preferred to swim in central area and most of the mice exhibited an even area distribution. Long-term exercise training improved cardiac systolic function and decreased blood pressure in mice, but hardly changed swimming behaviors. Analyses of the relationship between swimming behavior and cardiovascular adaptations to exercise training revealed that swimming behavior indicated the biological effects of swimming training. Specifically, mice which preferred swimming at the central zone or were trainable in behavior during 1-month training exhibited better outcomes in cardiac function and blood pressure post long-term exercise. Mechanistically, a centralized swimming behavior indicated a smaller stress during exercise, as evidenced by a milder activation of hypothalamic-pituitary-adrenal axis. Discussion: These results suggest that swimming behavior during training indicates individualized adaptations to long-term exercise, and highlight a biological significance of swimming behavior monitoring in animal studies.

Behavioral toxicity of TDCPP in marine zooplankton: Evidence from feeding and swimming responses, molecular dynamics and metabolomics of rotifers

As new organic flame retardants, chlorinated organophosphate esters (Cl-OPEs) have high water solubility and structural similarity to organophosphate pesticides, posing risks to aquatic organisms. The potential neurotoxicity of Cl-OPEs has attracted attention, especially in marine invertebrates with a relatively simple nervous system. In this study, a marine rotifer with a cerebral ganglion, Brachionus plicatilis, was exposed to tris (1,3-dichloro-2-propyl) phosphate (TDCPP) (two environmental concentrations and one extreme level), and the changes in feeding and swimming behaviors and internal mechanism were explored. Exposure to 1.05 nM TDCPP did not change the filtration and ingestion rates of rotifers and average linear velocity. But 0.42 and 4.20 μM TDCPP inhibited these three parameters and reduced unsaturated fatty acid content, reproduction and population growth. All TDCPP test concentrations suppressed AChE activity, causing excessive accumulation of acetylcholine within rotifers, thereby disturbing the neural innervation of corona cilia. Molecular docking and molecular dynamics revealed that this inhibition was because TDCPP can bind to the catalytic active site of rotifer AChE through van der Waals forces and electrostatic interactions. TRP420 was the leading amino residue in the binding, and GLY207 contributed to a hydrogen bond. Nontargeted metabolomics using LC-MS and GC-MS identified differentially expressed metabolites in TDCPP treatments, mainly from lipid and lipid-like molecules, especially sphingolipids. TDCPP decreased ganglioside content but stimulated ceramide generation and the expression levels of 3 genes related to ceramide de novo synthesis. The mitochondrial membrane potential (MMP) and ATP content decreased, and the electron respiratory chain complex and TCA cycle were deactivated. An inhibitor of ceramide synthase, fumonisin, alleviated MMP and ATP, implying a critical role of ceramide in mitochondrial dysfunction. Thus, TDCPP exposure caused an energy supply deficit affecting ciliary movement and ultimately inhibiting rotifer behaviors. Overall, this study promotes the understanding of the neurotoxicity of Cl-OPEs in marine invertebrates.

Comparison of Behavioral Effects of GABAergic Low- and High-Efficacy Neuroactive Steroids in the Zebrafish Larvae Assay.

Activation of the GABAA receptor is associated with numerous behavioral end points ranging from anxiolysis to deep anesthesia. The specific behavioral effect of a GABAergic compound is considered to correlate with the degree of its functional effect on the receptor. Here, we tested the hypothesis that a low-efficacy allosteric potentiator of the GABAA receptor may act, due to a ceiling effect, as a sedative with reduced and limited action. We synthesized a derivative, named (3α,5β)-20-methyl-pregnane-3,20-diol (KK-235), of the GABAergic neurosteroid 5β-pregnane-3α,20α-diol. Using electrophysiology, we showed that KK-235 is a low-efficacy potentiator of the synaptic-type α1β2γ2L GABAA receptor. In the zebrafish larvae behavioral assay, KK-235 was found to only partially block the inverted photomotor response (PMR) and to weakly reduce swimming behavior, whereas the high-efficacy GABAergic steroid (3α,5α,17β)-3-hydroxyandrostane-17-carbonitrile (ACN) fully blocked PMR and spontaneous swimming. Coapplication of KK-235 reduced the potentiating effect of ACN in an electrophysiological assay and dampened its sedative effect in behavioral experiments. We propose that low-efficacy GABAergic potentiators may be useful as sedatives with limited action.

Early ontogeny of the African bony-tongue (Heterotis niloticus) and the effect of Artemia and rotifer live feeds on larval digestive enzyme activity and performance

High larval and fry mortality has been a major challenge to the commercial culture of the African bony-tongue (Heterotis niloticus). Research indicates inadequate feeding to be a possible cause of the high mortality rates of larvae/fry grown in captivity. An experiment was conducted to first describe the developmental stages of H. niloticus eggs and larvae until schooling, 6 days after hatching (DAH), at 26°C. The morphological development, survival, growth (weight gain and length), and swimming behavior of the larvae were monitored. A follow-up feeding trial was conducted with H. niloticus fry from 6 to 27 DAH involving four treatments: feeding with Artemia nauplii; a combined feed of 50% Artemia nauplii and 50% rotifers (w/w); feeding with rotifers; and no feeding. The activities of three digestive enzymes (trypsin, lipase, and amylase) were assessed in fry exposed to the live feed treatments. At hatching, the larvae had a large, vascularized yolk sac filled with yolk platelets, which occupied approximately one-third of the total body length of the abdominal cavity. Yolk platelet reabsorption started at 1 DAH and was complete at 6 DAH. Metamorphosis was completed at 6 DAH, and schooling behavior was observed. For the feeding trial, the fry that received Artemia nauplii underwent the fastest development until 27 DAH. Similarly, the survival rate was considerably higher in fry fed with Artemia nauplii than in those that received a combination of Artemia nauplii and rotifers or only rotifers. Overall, the survival rates for fry fed with Artemia nauplii and larvae co-fed were 72.7% ± 0.9% and 41.2% ± 3.3%, respectively. Fry did not survive until 27 DAH in the rotifer-fed and unfed treatment groups. Digestive enzyme activity differed significantly (p&amp;lt; 0.05) between treatments and sampling dates. All digestive enzymes were detectable at the onset of mouth opening (5 DAH) and fluctuated through the 7 and 9 DAH. Lower enzyme activity was observed when the fry were subjected to starvation or the rotifer treatment. Results indicate that Artemia nauplii is the best live feed organism for H. niloticus larviculture.

Electromyography-Based Biomechanical Cybernetic Control of a Robotic Fish Avatar

This study introduces a cybernetic control and architectural framework for a robotic fish avatar operated by a human. The behavior of the robot fish is influenced by the electromyographic (EMG) signals of the human operator, triggered by stimuli from the surrounding objects and scenery. A deep artificial neural network (ANN) with perceptrons classifies the EMG signals, discerning the type of muscular stimuli generated. The research unveils a fuzzy-based oscillation pattern generator (OPG) designed to emulate functions akin to a neural central pattern generator, producing coordinated fish undulations. The OPG generates swimming behavior as an oscillation function, decoupled into coordinated step signals, right and left, for a dual electromagnetic oscillator in the fish propulsion system. Furthermore, the research presents an underactuated biorobotic mechanism of the subcarangiform type comprising a two-solenoid electromagnetic oscillator, an antagonistic musculoskeletal elastic system of tendons, and a multi-link caudal spine composed of helical springs. The biomechanics dynamic model and control for swimming, as well as the ballasting system for submersion and buoyancy, are deduced. This study highlights the utilization of EMG measurements encompassing sampling time and μ-volt signals for both hands and all fingers. The subsequent feature extraction resulted in three types of statistical patterns, namely, Ω,γ,λ, serving as inputs for a multilayer feedforward neural network of perceptrons. The experimental findings quantified controlled movements, specifically caudal fin undulations during forward, right, and left turns, with a particular emphasis on the dynamics of caudal fin undulations of a robot prototype.

Morphology and motor behavior of endemic fishes in the upper reaches of the Yangtze River basin.

Dam construction alters the hydrodynamic conditions, consequently impacting the swimming behavior of fish. To explore the effect of flow hydrodynamics on fish swimming behavior, five endemic fish species in the upper Yangtze River basin were selected. Through high-speed video visualization and computer analysis, these species' swimming patterns under different flow velocities (0.1-1.2 m/s) were investigated. The kinematic and morphological characteristics of the fish were presented. The principal component analysis was used to analyse the main factors influencing the swimming ability of fish and to determine the correlation coefficients among fish behavior indicators. Fish exhibited three different swimming patterns under different flow velocities. Low velocity (0.1-0.3 m/s) corresponds to free motion, middle velocity (0.4-0.7 m/s) corresponds to cruising motion, and high velocity corresponds to stress motion (0.8-1.2 m/s). The fish kinematic index curves were obtained, and four of five fish species showed two extreme points, which means the optimal and adverse swimming strategies can be determined. With the increase in flow velocity, the tail-beat frequency showed an increasing trend, whereas the tail-beat angle and amplitude showed a decreasing trend. Morphological and kinematic parameters were the two main indexes that affect the swimming ability of fish, which accounts for 41.9% and 26.9%, respectively.

FIRST REPORT OF RAPHIDASCARIS LOPHII INFECTION IN BLUEFIN SEAROBIN (CHELIDONICHTHYS SPINOSUS)

This study reports on diseased Chelidonichthys spinosus fish that were originally obtained from the Taiwan Strait for exhibition in an aquarium. These fish showed abnormal swimming behavior, eye damage and skin lesions. Gross examination and histopathology revealed that the C. spinosus was suffering from severe nematode infections in the pyloric caeca, liver and mesentery. Marine nematodes from internal organs were verified by partially sequencing the internal transcribed spacer (ITS) gene. Sequencing results revealed that the nematodes shared 99.75% sequence identity with Raphidascaris lophii (GenBank accession No. MW132926). Additionally, secondary Vibrio harveyi infections were also detected in some C. spinosus. This is the first report of R. lophii infection in C. spinosus.