Fish Model Research Articles

SDF-1/CXCR4 signal is involved in the induction of Primordial Germ Cell migration in a model marine fish, Japanese anchovy (Engraulis japonicus)

Primordial germ cells (PGCs) are pivotal for gonadal development and reproductive success. Though artificial induction of sterility by targeting PGCs are gaining popularity due to its advantages in fish surrogacy and biodiversity management, it is often skill and time intensive. In this study, we have focused on understanding the role of PGCs and the chemotactic SDF-1/CXCR4 signaling on gonad development of Japanese anchovy (JA, Engraulis japonicus), an upcoming marine model organism with eco-commercial values, with an aim to develop a novel, easy, and versatile gonad sterilization method. Our data showed that PGC migration related genes, i.e., sdf-1a, sdf-1b, cxcr4a, cxcr4b and vasa, are phylogenetically closer relatives of respective herring (Clupea harengus) and zebrafish (Danio rerio) homolog. Subsequently, PGC marking and live tracing experiments confirmed that PGC migration in JA initiates from 16 hours post fertilization (hpf) followed by PGC settlement in the gonadal ridge at 44 hpf. We found that overexpression of zebrafish sdf-1a mRNA in the germ cell suppresses cxcr4a and increases cxcr4b transcription at 8 hpf, dose dependently disrupts PGC migration at 24–48 hpf, induces PGC death and upregulates sdf-1b at 5 days post hatching. 48 h of immersion treatment with CXCR4 antagonist (AMD3100, Abcam) also accelerated PGC mismigration and pushed the PGC away from gonadal ridge in a dose responsive manner, and further when grown to adulthood caused germ cell less gonad formation in some individuals. Cumulatively, our data, for the first time, suggests that JA PGC migration is largely regulated by SDF1/CXCR4 signaling, and modulation of this signaling has strong potential for sterile, germ cell less gonad preparation at a mass scale. However, further in-depth analysis is pertinent to apply this methodology in marine fish species to successfully catapult Japanese anchovy into a true marine fish model.

Characterization of a Cournot–Nash Equilibrium for a Fishery Model with Fuzzy Utilities

The article deals with the extensions of discrete-time games with infinite time horizon and their application in a fuzzy context to fishery models. The criteria for these games are the total discounted utility and the average utility in a fishing problem. However, in the fuzzy case, game theory is not the best way to represent a real fishing problem because players do not always have enough information to accurately estimate their utility in the context of fishing. For this reason, in this paper, trapezoidal-type fuzzy utility values are considered for a fishing model, and the terms of the Nash equilibrium are given in the fuzzy context, i.e., this equilibrium is represented using the partial order of the α-cuts of the fuzzy numbers; to the best of the authors’ knowledge, there is no work with this type of treatment. To obtain each equilibrium, a suitable fully determined fuzzy game is used in combination with the dynamic programming technique applied to this game in the context of fishing. The main results are (i) the Nash equilibria of the fuzzy games coincide with the Nash equilibria of the nonfuzzy games and are explicitly determined in a fishery model and (ii) the values of the fuzzy games are of trapezoidal type and are also explicitly given in the fishery model.

A Study of The Fish Supply Chain at The Paotere Fishing Port of Makassar City

This study aims to determine (1) the flow of information and finance, (2) the main problems that occur in supply chain activities at PPI Paotere, and (3) supply chain models at PPI Paotere. This research was conducted in March 2021 at PPI Paotere, Makassar City. The type of research used is survey research using a quantitative approach. The sampling method used cluster sampling and the determination of the number of samples with the Slovin formula, so that the number of samples as many as 43 people. The data analysis used in this study is a quantitative and qualitative descriptive analysis. The results showed that in terms of information flow, pelagic and demersal fish sources of information mostly came from groups of fishermen, courtiers and even other traders. Financial flow with a system of mutual trust that has been built and maintained for a long time because the average supplier and trader have been subscribing for years. The flow of goods starts from the source of goods originating from fishermen who are obtained from nearby islands until they finally arrive to consumers and industry. There are various problems experienced by market players at the Paotere fishing port, including the timeliness of auctions, checking the number and types of fish and cooperative services at the Paotere fishing port. The supply chain model for pelagic and demersal fish in the Paotere fishing port is divided into two, namely for export needs and local consumers. The supply chain model for local consumer needs consists of groups of fishermen, courtiers, traders and consumers while for export needs consists of groups of fishermen, retainers, UPI, companies then exported.

Pathology, microbiology, and genetic diversity associated with Erysipelothrix rhusiopathiae and novel Erysipelothrix spp. infections in southern sea otters (Enhydra lutris nereis).

Erysipelothrix spp., including E. rhusiopathiae, are zoonotic bacterial pathogens that can cause morbidity and mortality in mammals, fish, reptiles, birds, and humans. The southern sea otter (SSO; Enhydra lutris nereis) is a federally-listed threatened species for which infectious disease is a major cause of mortality. We estimated the frequency of detection of these opportunistic pathogens in dead SSOs, described pathology associated with Erysipelothrix infections in SSOs, characterized the genetic diversity and antimicrobial susceptibility of SSO isolates, and evaluated the virulence of two novel Erysipelothrix isolates from SSOs using an in vivo fish model. From 1998 to 2021 Erysipelothrix spp. were isolated from six of >500 necropsied SSOs. Erysipelothrix spp. were isolated in pure culture from three cases, while the other three were mixed cultures. Bacterial septicemia was a primary or contributing cause of death in five of the six cases. Other pathology observed included suppurative lymphadenopathy, fibrinosuppurative arteritis with thrombosis and infarction, bilateral uveitis and endophthalmitis, hypopyon, petechia and ecchymoses, mucosal infarction, and suppurative meningoencephalitis and ventriculitis. Short to long slender Gram-positive or Gram-variable bacterial rods were identified within lesions, alone or with other opportunistic bacteria. All six SSO isolates had the spaA genotype-four isolates clustered with spaA E. rhusiopathiae strains from various terrestrial and marine animal hosts. Two isolates did not cluster with any known Erysipelothrix spp.; whole genome sequencing revealed a novel Erysipelothrix species and a novel E. rhusiopathiae subspecies. We propose the names Erysipelothrix enhydrae sp. nov. and Erysipelothrix rhusiopathiae ohloneorum ssp. nov. respectively. The type strains are E. enhydrae UCD-4322-04 and E. rhusiopathiae ohloneorum UCD-4724-06, respectively. Experimental injection of tiger barbs (Puntigrus tetrazona) resulted in infection and mortality from the two novel Erysipelothrix spp. Antimicrobial susceptibility testing of Erysipelothrix isolates from SSOs shows similar susceptibility profiles to isolates from other terrestrial and aquatic animals. This is the first description of the pathology, microbial characteristics, and genetic diversity of Erysipelothrix isolates recovered from diseased SSOs. Methods presented here can facilitate case recognition, aid characterization of Erysipelothrix isolates, and illustrate assessment of virulence using fish models.

Modeling the importance of subsurface environmental variables in driving swordfish (Xiphias gladius) catchability in the Western Indian Ocean

AbstractMany oceanic species in pelagic habitats move vertically through the water column, highlighting the ecological importance of that spatial environment for modeling habitats of marine species. The role and importance of multiple oceanic subsurface environmental variables in modeling the habitat suitability of swordfish (Xiphias gladius), a highly migratory large pelagic fish, is poorly understood. In this study, we analyzed adult swordfish data from the 2017–2019 Chinese Indian Ocean tuna longline fishery observer. We used the maximum entropy model (MaxEnt) and random forest model (RF) to compare modeling schemes that included multiple subsurface environmental datasets. The area under receiver operating characteristic curve (AUC) from training and test sets was evaluated to investigate whether the inclusion of subsurface variables could enhance model performance and affect the simulation results. This analysis showed that model performance was significantly enhanced after addition of subsurface environmental variables, and the best model fit was achieved at 200–300 m depth. Sea water temperature, dissolved oxygen, net primary production, and ocean mixed layer depth were the critical environmental factors constituting catchability for swordfish in the Western Indian Ocean. As the depth increased, dissolved oxygen became the most important environmental factor, replacing surface temperature. Compared with the surface model, the location and extent of areas of high catchability in certain months changed significantly after the addition of subsurface variables. The results of this study provide evidence for a better understanding of the selection of critical environmental variables and improvement of model performance in 3D habitat modeling of pelagic fish.

Higher intake of β-glucan impairs reproduction in a female teleost, Tor putitora (Hamilton, 1822).

Although the immuno-modulatory and stress-relieving properties of β-glucan is well elucidated in humans and other animal models, including fish, its role as a dietary supplement on reproduction is extremely scarce. Therefore, in this study, adult female fish were fed one of four test diets having 0 (control), 0.5, 1, and 1.5% β-D-glucan for 130 days and its effect on reproductive performance, ovarian and liver histology, sex hormones, and transcript abundance of selected reproduction-related genes was assessed. Low dietary intake of β-glucan improved fertilization and hatching rates (p<0.05). The relative fecundity and percentage of spawning females were higher (non-significant) in 0.5% β-glucan-fed groups. Surprisingly, even after 130 days, spawning did not occur in 1.5% β-glucan-fed individuals. Irrespective of β-glucan intake, all the brooders recorded similar plasma 17β-estradiol and maturation-inducing hormone (p>0.05). Higher intake of β-glucan (1.5%) upregulated aromatase genes without a parallel increase in 17β-estradiol. However, plasma vitellogenin increased with increasing β-glucan up to 1.0% then declined at 1.5% (p<0.05). The fish that received control, 0.5, and 1.5% β-glucan recorded similar vitellogenin levels in their plasma. Significantly higher plasma cortisol was evidenced in 1.5% β-glucan fed brooders (p<0.05). Histologically, higher follicular atresia and leaking of yolk material was evidenced in 1.5% β-glucan-fed group. Liver histology revealed the highest nutrient/lipid accumulation in fish that received 1.0% and 1.5% β-glucan. This study demonstrated the stimulatory effect of β-glucan intake at a lower dose (0.5%) on reproduction. However, higher intake (1.5%) could perturb normal reproductive function in a fish model and caused an increased number of atretic follicles leading to spawning/reproductive failure.

Dose addition in mixtures of compounds with dissimilar endocrine modes of action in in vitro receptor activation assays and the zebrafish sexual development test

BackgroundHuman exposure to pesticides is being associated with feminisation for which a decrease of the anogenital distance (AGD) is a sensitive endpoint. Dose addition for the cumulative risk assessment of pesticides in food is considered sufficiently conservative for combinations of compounds with both similar and dissimilar modes of action (MoA). ObjectiveThe present study was designed to test the dose addition hypothesis in a binary mixture of endocrine active compounds with a dissimilar mode of action for the endpoint feminisation. MethodsCompounds were selected from a list of chemicals of which exposure is related to a decrease of the AGD in rats and completed with reference compounds. These chemicals were characterised using specific in vitro transcriptional activation (TA) assays for estrogenic and androgenic properties, leading to a final selection of dienestrol as an ER-agonist and flutamide, linuron, and deltamethrin as AR-antagonists. These compounds were then tested in an in vivo model, i.e. in zebrafish (Danio rerio), using sex ratio in the population as an endpoint in order to confirm their feminising effect and MoA. Ultimately, the fish model was used to test a binary mixture of flutamide and dienestrol. ResultsStatistical analysis of the binary mixture of flutamide and dienestrol in the fish sexual development tests (FSDT) with zebrafish supported dose addition.

Procedural Fish Modeling.

It is time- and man-power intensive to craft various fish species for underwater animations and games. Even professionals spend hours to days for one. Therefore, we propose Procedural Fish Generation, which presents an innovative and automatic approach to generate 3D fish models with one lateral image. The core lies in parameterizing the ray-finned fish with curves and optimizing them with textures to fit the input using differentiable rendering, greatly reducing the manual modeling work. It presents advantages over multi-image reconstruction in requiring single image, while state-of-the-art methods suffer from such a scenario to achieve informative reconstruction. Also, our method outputs a polygon mesh, widely compatible with modern graphics hardware and software, thus facilitating further editing. Furthermore, we fine tune the prompts for Stable Diffusion while users can type a name to find high-quality lateral images. Extensive ablation studies and comparisons have proved its effectiveness and efficiency for experts and non-experts.

Troxerutin Exerts Anti-Pulmonary Fibrosis Activity in Nicotine-Induced Lung Fibrosis on Zebra Fish Model

Troxerutin Exerts Anti-Pulmonary Fibrosis Activity in Nicotine-Induced Lung Fibrosis on Zebra Fish Model

Development and validation of a Medaka fish voxel-based model for internal ionizing radiation dosimetry

In this paper, we present a voxel-based phantom of Medaka fish that can be used to assess the internal radiation doses that would be absorbed by different organs of this fish species if exposed to radioactive wastewater released into the ocean. The geometric model for fish was generated based on available Wavefront Object files for smooth-bodied Medaka fish organs, whereas due to the lack of Medaka fish material specification, the material model was constructed using material data appropriate to ICRP 110 adult male voxel-based phantom. Absorbed Fractions (AFs) and Specific Absorbed Fractions (SAFs) were calculated for eight organs of major interest as sources and for each organ as target at a set of discrete photon, electron, alpha and neutron energies. To validate the present model the calculated AFs in the studied organs were compared to ones obtained in similar organs in a voxel-based phantom of another teleost fish species called Limanda limanda. The results presented are consistent with the reference dosimetric data. We concluded that the Medaka model can be used in radioecology research to improve marine radiation protection.

Maternal or Paternal Antibiotics? Intergenerational Transmission and Reproductive Toxicity in Zebrafish.

Despite the known direct toxicity of various antibiotics to aquatic organisms, the potential chronic impact through intergenerational transmission on reproduction remains elusive. Here, we exposed zebrafish to a mixture of 15 commonly consumed antibiotics at environmentally relevant concentrations (1 and 100 μg L-1) with a cross-mating design. A high accumulation of antibiotics was detected in the ovary (up to 904.58 ng g-1) and testis (up to 1704.49 ng g-1) of F0 fish. The transmission of antibiotics from the F0 generation to the subsequent generation (F1 offspring) was confirmed with a transmission rate (ki) ranging from 0.11 to 2.32. The maternal transfer of antibiotics was significantly higher, relative to paternal transfer, due to a greater role of transmission through ovarian enrichment and oviposition compared to testis enrichment. There were similar impairments in reproductive and developmental indexes on F1 eggs found following both female and male parental exposure. Almost all antibiotics were eliminated in F2 eggs in comparison to F1 eggs. However, there were still reproductive and developmental toxic responses observed in F2 fish, suggesting that antibiotic concentration levels were not the only criterion for evaluating the toxic effects for each generation. These findings unveil the intergenerational transmission mechanism of antibiotics in fish models and underscore their potential and lasting impact in aquatic environments.

Development of the bioinspired propulsion system for a robotic fish

Biomimetic robots aim to replicate the movement principles of living creatures, which have been continuously perfected by nature to ensure survival. Technically, survival comprises two factors: optimizing movement efficacy, such as speed, distance traveled, or acceleration, and minimizing energy consumption during movement. Researchers have made several attempts to develop a biomimetic fish robot [1–3]. Tunas are a group of fish with numerous evolutionary adaptations that make them exceptional swimmers, including tail shape, lateral peduncle keels, pectoral fin shape, and finlets. Thunniform locomotion is characterized by limited undulation, typically restricted to the rear one-third of the body, with maximal amplitude reached at the end of the tail peduncle. A bioinspired propulsion system was developed for a robotic fish model. It is based on the combination of an elastic cord with a tail fin that is firmly attached to the cord. Two symmetric movable thrusts that simulate muscle contractions connect the tail fin to a servomotor. The propulsion system provides oscillatory tail movement that can be controlled for amplitude and frequency. This movement translates to the movement of the robotic fish, which executes the thunniform principle of locomotion. The body and tail fin of the robotic fish were designed using a computational model that simulates a virtual body in water. Subsequently, we constructed a prototype of the robotic fish and tested it under experimental conditions. Experiments were conducted to investigate the relationship between the robot’s kinematics and the dynamic parameters of the propulsion system. The results showed that increasing the frequency of tail fin oscillations led to an increase in the robot’s speed. At fixed frequencies, there was an interval of energetically efficient travel speeds up to a threshold velocity. Movement at higher speeds was achievable; however, it was accompanied by greater power consumption. The conclusion aligns with the data from COT studies on living tunas, indicating qualitative agreement. However, the robot’s values were quantitatively higher. Our robotic fish reached a maximum speed of approximately 0.4 BL/s, exceeding speeds in other works where a simplified tail section was used (0.22 BL/s [4], 0.254 BL/s [5]). Our study demonstrated a correlation between the efficiency of robot swimming and amplitude, which was previously unexplored in addition to previous findings on the relationship between tail beat frequency and swimming speed, as well as the dependence of frequency and swimming speed. The results showed that increasing the oscillation amplitude of the propulsion system, at a fixed frequency, only led to a rise in swimming speed up to a certain threshold. However, further increases in amplitude resulted in minimal speed increases at higher energy costs. An evaluation of energy efficiency was conducted, assessing its dependence on dynamic parameters of tail oscillation. The results show that the transport cost rises as the tail amplitude rises beyond the threshold. Furthermore, it was found that for a fixed frequency, an interval of energetic preferred speeds up to a threshold exists. Although moving at a higher speed is possible, it consumes more power. In general, it is preferable to increase caudal fin oscillation frequency rather than amplitude to increase swimming speed. These findings are in qualitative accordance with the outcomes of the numerical simulation of thunniform swimming.

The Role of MAPRE2 and Microtubules in Maintaining Normal Ventricular Conduction.

Brugada syndrome is associated with loss-of-function SCN5A variants, yet these account for only ≈20% of cases. A recent genome-wide association study identified a novel locus within MAPRE2, which encodes EB2 (microtubule end-binding protein 2), implicating microtubule involvement in Brugada syndrome. A mapre2 knockout zebrafish model was generated using CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/clustered regularly interspaced short palindromic repeat-associated protein 9) and validated by Western blot. Larval hearts at 5 days post-fertilization were isolated for voltage mapping and immunocytochemistry. Adult fish hearts were used for ECG, patch clamping, and immunocytochemistry. Morpholinos were injected into embryos at 1-cell stage for knockdown experiments. A transgenic zebrafish line with cdh2 tandem fluorescent timer was used to study adherens junctions. Microtubule plus-end tracking and patch clamping were performed in human induced pluripotent stem cell derived cardiomyocytes (iPSC-CMs) with MAPRE2 knockdown and knockout, respectively. Voltage mapping of mapre2 knockout hearts showed a decrease in ventricular maximum upstroke velocity of the action potential and conduction velocity, suggesting loss of cardiac voltage-gated sodium channel function. ECG showed QRS prolongation in adult knockout fish, and patch clamping showed decreased sodium current density in knockout ventricular myocytes and arrhythmias in knockout iPSC-CMs. Confocal imaging showed disorganized adherens junctions and mislocalization of mature Ncad (N-cadherin) with mapre2 loss of function, associated with a decrease of detyrosinated tubulin. MAPRE2 knockdown in iPSC-CMs led to an increase in microtubule growth velocity and distance, indicating changes in microtubule dynamics. Finally, knockdown of ttl encoding tubulin tyrosine ligase in mapre2 knockout larvae rescued tubulin detyrosination and ventricular maximum upstroke velocity of the action potential. Genetic ablation of mapre2 led to a decrease in voltage-gated sodium channel function, a hallmark of Brugada syndrome, associated with disruption of adherens junctions, decrease of detyrosinated tubulin as a marker of microtubule stability, and changes in microtubule dynamics. Restoration of the detyrosinated tubulin fraction with ttl knockdown led to rescue of voltage-gated sodium channel-related functional parameters in mapre2 knockout hearts. Taken together, our study implicates microtubule dynamics in the modulation of ventricular conduction.

Modeling familial and sporadic Parkinson's disease in small fishes.

The establishment of animal models for Parkinson's disease (PD) has been challenging. Nevertheless, once established, they will serve as valuable tools for elucidating the causes and pathogenesis of PD, as well as for developing new strategies for its treatment. Following the recent discovery of a series of PD causative genes in familial cases, teleost fishes, including zebrafish and medaka, have often been used to establish genetic PD models because of their ease of breeding and gene manipulation, as well as the high conservation of gene orthologs. Some of the fish lines can recapitulate PD phenotypes, which are often more pronounced than those in rodent genetic models. In addition, a new experimental teleost fish, turquoise killifish, can be used as a sporadic PD model, because it spontaneously manifests age-dependent PD phenotypes. Several PD fish models have already made significant contributions to the discovery of novel PD pathological features, such as cytosolic leakage of mitochondrial DNA and pathogenic phosphorylation in α-synuclein. Therefore, utilizing various PD fish models with distinct degenerative phenotypes will be an effective strategy for identifying emerging facets of PD pathogenesis and therapeutic modalities.

Genome-wide identification and characterization of tissue specific long non-coding RNAs and circular RNAs in common carp (Cyprinus carpio L.)

Cyprinus carpio is regarded as a substitute vertebrate fish model for zebrafish. A varied category of non-coding RNAs is comprised of long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs). These ncRNAs were once considered non-functional “junk DNA” but research now shows they play important roles in gene expression regulation, chromatin modification, and epigenetic regulation. The systemic tissue-specific research of the lncRNAs and circRNAs of C. carpio is yet unexplored. A total of 468 raw RNA-Seq dataset across 28 distinct tissues from different varieties of common carp retrieved from public domain were pre-processing, mapped and assembled for lncRNA identification/ classification using various bioinformatics tools. A total of 33,990 lncRNAs were identified along with revelation of 9 miRNAs having 19 unique lncRNAs acting as their precursors. Additionally, 2,837 miRNAs were found to target 4,782 distinct lncRNAs in the lncRNA-miRNA-mRNA interaction network analysis, which resulted in the involvement of 3,718 mRNAs in common carp. A total of 22,854 circRNAs were identified tissue-wise across all the 28 tissues. Moreover, the examination of the circRNA-miRNA-mRNA interaction network revealed that 15,731 circRNAs were targeted by 5,906 distinct miRNAs, which in turn targeted 4,524 mRNAs in common carp. Significant signaling pathways like necroptosis, NOD-like receptor signaling pathway, hypertrophic cardiomyopathy, small cell lung cancer, MAPK signaling pathway, etc. were identified using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes. The web resource of common carp ncRNAs, named CCncRNAdb and available at http://backlin.cabgrid.res.in/ccncrnadb/ gives a comprehensive information about common carp lncRNAs, circRNAs, and ceRNAs interactions, which can aid in investigating their functional roles for its management.

Phylogenetic structure of body shape in a diverse inland ichthyofauna

Body shape is a fundamental metric of animal diversity affecting critical behavioral and ecological dynamics and conservation status, yet previously available methods capture only a fraction of total body-shape variance. Here we use structure-from-motion (SFM) 3D photogrammetry to generate digital 3D models of adult fishes from the Lower Mississippi Basin, one of the most diverse temperate-zone freshwater faunas on Earth, and 3D geometric morphometrics to capture morphologically distinct shape variables, interpreting principal components as growth fields. The mean body shape in this fauna resembles plesiomorphic teleost fishes, and the major dimensions of body-shape disparity are similar to those of other fish faunas worldwide. Major patterns of body-shape disparity are structured by phylogeny, with nested clades occupying distinct portions of the morphospace, most of the morphospace occupied by multiple distinct clades, and one clade (Acanthomorpha) accounting for over half of the total body shape variance. In contrast to previous studies, variance in body depth (59.4%) structures overall body-shape disparity more than does length (31.1%), while width accounts for a non-trivial (9.5%) amount of the total body-shape disparity.

Complex dynamics of a fishery model: Impact of the triple effects of fear, cooperative hunting and intermittent harvesting

In natural ecosystems, predators often live in groups and have evolved cooperative hunting behaviors over time. This cooperative behavior on the one hand increases the success rate of the prey, but it also leads to the fear response of prey to predators, thereby affecting the reproduction rate of prey populations. In the current study, we put forward a fishery model for renewable aquatic resource with dual effects of fear and cooperative hunting, and investigate the impact of fear level and cooperative hunting intensity on the dynamics of the model. The analysis shows that the level of fear and the intensity of cooperative hunting can affect the existence and number of coexisting equilibria. Secondly, from the perspective of rational exploitation of fishery resources, we adopt a state-feedback intermittent fishing strategy, which fully considers the current status of the target species and avoids the impact of irrational fishing on the ecosystem. We investigate the dynamic behavior of the fishery model under discontinuous fishing model, including the existence and stability of predator-extinction periodic solution and co-existence order-1 and order-2 periodic solutions under different fishing thresholds, which not only provides a possibility to fishing species according to the period, but also ensures a certain robustness of the fishing strategy. Finally, the main results are verified by numerical simulations using MATLAB program and their biological implications are discussed.

Trajectory Tracking and Obstacle Avoidance of Robotic Fish Based on Nonlinear Model Predictive Control.

The attainment of accurate motion control for robotic fish inside intricate underwater environments continues to be a substantial obstacle within the realm of underwater robotics. This paper presents a proposed algorithm for trajectory tracking and obstacle avoidance planning in robotic fish, utilizing nonlinear model predictive control (NMPC). This methodology facilitates the implementation of optimization-based control in real-time, utilizing the present state and environmental data to effectively regulate the movements of the robotic fish with a high degree of agility. To begin with, a dynamic model of the robotic fish, incorporating accelerations, is formulated inside the framework of the world coordinate system. The last step involves providing a detailed explanation of the NMPC algorithm and developing obstacle avoidance and objective functions for the fish in water. This will enable the design of an NMPC controller that incorporates control restrictions. In order to assess the efficacy of the proposed approach, a comparative analysis is conducted between the NMPC algorithm and the pure pursuit (PP) algorithm in terms of trajectory tracking. This comparison serves to affirm the accuracy of the NMPC algorithm in effectively tracking trajectories. Moreover, a comparative analysis between the NMPC algorithm and the dynamic window approach (DWA) method in the context of obstacle avoidance planning highlights the superior resilience of the NMPC algorithm in this domain. The proposed strategy, which utilizes NMPC, demonstrates a viable alternative for achieving precise trajectory tracking and efficient obstacle avoidance planning in the context of robotic fish motion control within intricate surroundings. This method exhibits considerable potential for practical implementation and future application.

Vortex phase matching of a self-propelled model of fish with autonomous fin motion

It has been a long-standing problem how schooling fish optimize their motion by exploiting the vortices shed by the others. A recent experimental study showed that a pair of fish reduce energy consumption by matching the phases of their tailbeat according to their distance. In order to elucidate the dynamical mechanism by which fish control the motion of caudal fins via vortex-mediated hydrodynamic interactions, we introduce a new model of a self-propelled swimmer with an active flapping plate. The model incorporates the role of the central pattern generator network that generates rhythmic but noisy activity of the caudal muscle, in addition to hydrodynamic and elastic torques on the fin. For a solitary fish, the model reproduces a linear relation between the swimming speed and tailbeat frequency, as well as the distributions of the speed, tailbeat amplitude, and frequency. For a pair of fish, both the distribution function and energy dissipation rate exhibit periodic patterns as functions of the front-back distance and phase difference of the flapping motion. We show that a pair of fish spontaneously adjust their distance and phase difference via hydrodynamic interaction to reduce energy consumption.

Morphological Сharacterization of the Spinal Cord Regeneration in Adult Desert Killifish Aphaniops hormuzensis (Aphaniidae)

Morphological characterization of the lumbar spinal cord regeneration process was investigated in killifish A. hormuzensis, by using hematoxylin-eosin staining after spinal cord injury. An spinal cord injury was settled, and the injured tissue was sampled. Immediately after the spinal cord injury, the blood clot formation was detected at the injury epicenter and the ependymal layer, and at six hours post-injury (6 hpi), the inflammation and cavity formation occurred. The neural cell accumulation and beginning signs of the spinal cord regeneration were detected one-day post-injury (1 dpi) close to the ependymal layer and subependymal layer. In two 2 dpi, the tissue repair and regeneration progress were detected. The reformation of the ependymal canal happened at 3 dpi, followed by the completion of spinal cord regeneration at 5 dpi. The spinal cord regeneration potency in A. hormuzensis is relatively higher than in other traditional fish models. Studies on the regeneration of this interesting fish are new, therefore, further investigations are needed to explore additional information about various aspects of tissue regeneration. This study is important because killifishes have a short life span, show high environmental variation tolerance, and are easy to maintain and breed in laboratory conditions.