Hydrodynamic pressure sensing for a biomimetic robotic fish caudal fin integrated with a resistive pressure sensor.

Micro-sensors, such as pressure and flow sensors, are usually adopted to attain actual fluid information around swimming biomimetic robotic fish for hydrodynamic analysis and control. However, most of the reported micro-sensors are mounted discretely on body surfaces of robotic fish and it is impossible to analyzed the hydrodynamics between the caudal fin and the fluid. In this work, a biomimetic caudal fin integrated with a resistive pressure sensor is designed and fabricated by laser machined conductive carbon fibre composites. To analyze the pressure exerted on the caudal fin during underwater oscillation, the pressure on the caudal fin is measured under different oscillating frequencies and angles. Then a model developed from Bernoulli equation indicates that the maximum pressure difference is linear to the quadratic power of the oscillating frequency and the maximum oscillating angle. The fluid disturbance generated by caudal fin oscillating increases with an increase of oscillating frequency, resulting in the decrease of the efficiency of converting the kinetic energy of the caudal fin oscillation into the pressure difference on both sides of the caudal fin. However, perhaps due to the longer stability time of the disturbed fluid, this conversion efficiency increases with the increase of the maximum oscillating angle. Additionally, the pressure variation of the caudal fin oscillating with continuous different oscillating angles is also demonstrated to be detected effectively. It is suggested that the caudal fin integrated with the pressure sensor could be used for sensing thein situflow field in real time and analyzing the hydrodynamics of biomimetic robotic fish.

Adult caudal fin shape is imprinted in the embryonic fin fold.

Appendage shape is formed during development (and re-formed during regeneration) according to spatial and temporal cues that orchestrate local cellular morphogenesis. The caudal fin is the primary appendage used for propulsion in most fish species, and exhibits a range of distinct morphologies adapted for different swimming strategies, however the molecular mechanisms responsible for generating these diverse shapes remain mostly unknown. In zebrafish, caudal fins display a forked shape, with longer supportive bony rays at the periphery and shortest rays at the center. Here, we show that a premature, transient pulse of sonic hedgehog a (shha) overexpression during late embryonic development results in excess proliferation and growth of the central rays, causing the adult caudal fin to grow into a triangular, truncate shape. Both global and regional ectopic shha overexpression are sufficient to alter fin shape, and forked shape may be rescued by subsequent treatment with an antagonist of the canonical Shh pathway. The induced truncate fins show a decreased fin ray number and fail to form the hypural diastema that normally separates the dorsal and ventral fin lobes. While forked fins regenerate their original forked morphology, truncate fins regenerate truncate, suggesting that positional memory of the fin rays can be permanently altered by a transient treatment during embryogenesis. Ray finned fish have evolved a wide spectrum of caudal fin morphologies, ranging from truncate to forked, and the current work offers insights into the developmental mechanisms that may underlie this shape diversity.

Exploring the wound healing potential of Lobostemon fruticosus using in vitro and in vivo bioassays.

ETHNOPHARMACOLOGICAL RELEVANCE: Lobostemon fruticosus (L.) H.Buek is a perennial and woody shrub of the Boraginaceae family, found in the Cape region of South Africa. The leaves and twigs are used to treat dermatological conditions such as wounds, burns, ringworm, erysipelas and eczema. Anti-inflammatory, antibacterial, antiviral and anti-proliferative activities of L. fruticosus have been reported. However, there is a void in research which reports on the wound healing properties of this plant. AIM OF THE STUDY: Aligned with the traditional use of L. fruticosus, our study aimed to use in vitro and in vivo bioassays to confirm the wound healing potential of the plant. MATERIALS AND METHODS: An aqueous methanol extract (80% v/v) of L. fruticosus was prepared using a sample collected from the Western Cape Province of South Africa and chromatographically profiled by ultra-performance liquid chromatography coupled to mass spectrometry (UPLC-MS). The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity assay was performed to screen the non-toxic concentrations of the extract for subsequent use in the in vitro scratch assay. Both the human keratinocyte (HaCaT) and fibroblast (BJ-5ta) cell lines were employed in the in vitro scratch assay. The in vivo caudal fin amputation assay was used to assess the wound healing potential of L. fruticosus, by monitoring fin regeneration in zebrafish larvae treated with the plant extract at various concentrations. RESULTS: Six major compounds were tentatively identified in the L. fruticosus extract namely; globoidnan A, globoidnan B, rutin, rabdosiin, sagerinic acid and rosmarinic acid. The potentially toxic pyrrolizidine alkaloids were also identified and quantitatively confirmed to be present at a low concentration of 119.58 ppm (m/m). Treatment of HaCaT and BJ-5ta cells with the plant extract in the scratch assay resulted in an increase in cell migration, which translates to accelerated wound closure. After 24 hr treatment with 100 µg/mL of extract, wound closure was recorded to be 91.1±5.7% and 94.1±1.3% for the HaCaT and BJ-5ta cells, respectively, while the untreated (medium) controls showed 72.3±3.3% and 73.0±4.3% for the two cell lines, respectively. Complete wound closure was observed between 24 and 36 hr, while the untreated control group did not achieve 100% wound closure by the end of the observation period (48 hr). In vivo, the crude extract at 100 µg/mL accelerated zebrafish caudal fin regeneration achieving 100.5±3.8% regeneration compared to 68.3±6.6% in the untreated control at two days post amputation. CONCLUSIONS: The study affirms the wound healing properties, as well as low toxicity of L. fruticosus using both in vitro and in vivo assays, which supports the traditional medicinal use. Other in vitro assays that target different mechanisms involved in wound healing should be investigated to support the current findings.

Numerical Study on the Hydrodynamic Performance of a Flexible Caudal Fin with Different Trailing-Edge Shapes.

This paper presents a three-dimensional fluid-structure-coupled simulation of a flexible caudal fin with different trailing-edge shapes. The influences of caudal-fin shape on hydrodynamic performance are investigated by comparing the results of a simplified model of a square caudal fin with forked and deeply forked caudal fins under a wider range of non-dimensional flapping frequency, 0.6 < f* < 1.5, where f* is the ratio of flapping frequency to the natural frequency of each caudal fin, i.e., f* = f/fn. The leading edge of each caudal fin is forced to oscillate vertically in a water tank with zero free-stream conditions. The numerical results show that the amount of forking in the geometry of the caudal fin has significant effects on its hydrodynamic performance. A comparison of thrust coefficients shows that the square caudal fin has a greater thrust coefficient in the non-dimensional frequency range of 0.6 < f* < 1.2, while the deeply forked caudal fin generates higher thrust when 1.2 < f* < 1.5. In terms of propulsive efficiency, the square caudal fin is more efficient when 0.6 < f* < 0.9, while the propulsive efficiency of a deeply forked caudal fin is significantly enhanced when 0.9 < f* < 1.5. Based on our results, the deeply forked caudal fin has greater thrust coefficients and a higher propulsive efficiency in a higher frequency range than the natural frequency of each caudal fin. The thrust characteristics and flow fields around each caudal fin are investigated in detail.

Development of an Undergraduate Cell Biology Laboratory to Assess Pigmentation and Cell Size in a Zebrafish Model of Uveal Melanoma.

This study outlines a 2-week laboratory module for an authentic cell biology undergraduate research experience that uses zebrafish (Danio rerio), a popular model organism for research. Previous research has indicated that course-based undergraduate research experiences such as this one increase student confidence, active learning, and retention. During this research experience, students investigate variations in pigmentation in the caudal fins of wild type (WT) and transgenic fish [Tg(mitfa:GNAQQ209L)]. The transgenic fish express a hyperactive Gα protein, GNAQQ209L, under the melanocyte-specific mitfa promoter, offering insights into uveal melanoma, a common eye cancer. Students specifically analyze the black pigmented cells, melanophores, within the caudal fin. We determined that the transgenic zebrafish have increased pigmentation in their caudal fins, but smaller melanophores. These results suggest there are more melanophores in the Tg(mitfa:GNAQQ209L) fish compared to the WT. Future undergraduate research could investigate these cellular differences. This research experience imparts microscopy and image analysis skills and instills the ability to grapple with large datasets, statistical tests, and data interpretation in alignment with biology education principles. Post-laboratory surveys reveal students attain confidence in the above skills and in handling animals, along with a deeper appreciation for model organism research and its relevance to cancer cell biology.

Tail shape and the swimming speed of sharks.

Trait-based ecology is a rapidly growing approach for developing insights and predictions for data-poor species. Caudal tail fin shape has the potential to reveal much about the energetics, activity and ecology of fishes and can be rapidly measured from field guides, which is particularly helpful for data-sparse species. One outstanding question is whether swimming speed in sharks is related to two morphological traits: caudal fin aspect ratio (CFAR, height2/tail area) and caudal lobe asymmetry ratio (CLAR). We derived both metrics from the species drawings in Sharks of the world (Ebert et al. 2013 Sharks of the world: a fully illustrated guide) and related fin shape to two published datasets of (1) instantaneous swimming speeds (Jacoby et al. 2015 Biol. Lett. 11, 20150781 (doi:10.1098/rsbl.2015.0781)) and (2) cruising speeds (Harding et al. 2021 Funct. Ecol. 35, 1951-1959 (doi:10.1111/1365-2435.13869)) for 28 total unique shark species. Both estimates of swimming speed were positively related to CFAR (and weakly negatively to CLAR). Hence, shark species with larger CFAR and more symmetric tails (low CLAR) tended to be faster-moving and have higher average speeds. This relationship demonstrates the opportunity to use tail shape as an easily measured trait to index shark swimming speed to broader trait-based analyses of ecological function and extinction risk.

Metagenomic profile of caudal fin morphology of farmed red sea bream Pagrus major.

The morphology of farm-reared fish often differs from that of their wild counterparts, impacting their market value. Two caudal fin tip shapes, acutely angled and blunted, are recognized in farmed populations of red sea bream Pagrus major. The angled form is preferred by consumers over the blunt since it resembles that of wild fish. Discovering the cause of the blunted tip is crucial to maximizing the commercial value of farmed red sea bream. We hypothesized that the blunt fin tip is the result of opportunistic bacteria and conducted partial 16S rRNA metagenomic barcoding and generated a clone library of the 16S rRNA gene to compare bacterial communities of the 2 fin forms. Metagenomic barcoding revealed an abundance of 5 bacterial genera, Sulfitobacter, Vibrio, Tenacibaculum, Psychrobacter, and an unknown genus of Rhodobacteraceae, on the caudal fin surface. Sulfitobacter was significantly more common on the angled caudal fin than the blunted. Vibrio is the dominant genus on the blunted caudal fin. The clone library identified these genera to species level, and Sulfitobacter sp., Vibrio harveyi, Tenacibaculum maritimum, and Psychrobacter marincola were frequently observed in blunt caudal fins. Our results suggest that opportunistic pathogenic bacteria such as V. harveyi and T. maritimum are not the primary cause of caudal fin malformation, and multiple factors such as combinations of injury, stress, and pathogenic infection may be involved. The reason for the significantly greater occurrence of Sulfitobacter sp. in the angled caudal fin is unknown, and further investigation is needed.

Temporally and regionally distinct morphogenetic processes govern zebrafish caudal fin blood vessel network expansion.

Blood vessels form elaborate networks that depend on tissue-specific signalling pathways and anatomical structures to guide their growth. However, it is not clear which morphogenetic principles organize the stepwise assembly of the vasculature. We therefore performed a longitudinal analysis of zebrafish caudal fin vascular assembly, revealing the existence of temporally and spatially distinct morphogenetic processes. Initially, vein-derived endothelial cells (ECs) generated arteries in a reiterative process requiring vascular endothelial growth factor (Vegf), Notch and cxcr4a signalling. Subsequently, veins produced veins in more proximal fin regions, transforming pre-existing artery-vein loops into a three-vessel pattern consisting of an artery and two veins. A distinct set of vascular plexuses formed at the base of the fin. They differed in their diameter, flow magnitude and marker gene expression. At later stages, intussusceptive angiogenesis occurred from veins in distal fin regions. In proximal fin regions, we observed new vein sprouts crossing the inter-ray tissue through sprouting angiogenesis. Together, our results reveal a surprising diversity among the mechanisms generating the mature fin vasculature and suggest that these might be driven by separate local cues.

A tale of two fish tails: does a forked tail really perform better than a truncate tail when cruising?

Many fishes use their tail as the main thrust producer during swimming. This fin's diversity in shape and size influences its physical interactions with water as well as its ecological functions. Two distinct tail morphologies are common in bony fishes: flat, truncate tails which are best suited for fast accelerations via drag forces, and forked tails that promote economical, fast cruising by generating lift-based thrust. This assumption is based primarily on studies of the lunate caudal fin of Scombrids (i.e. tuna, mackerel), which is comparatively stiff and exhibits an airfoil-type cross-section. However, this is not representative of the more commonly observed and taxonomically widespread flexible forked tail, yet similar assumptions about economical cruising are widely accepted. Here, we present the first comparative experimental study of forked versus truncate tail shape and compare the fluid mechanical properties and energetics of two common nearshore fish species. We examined the hypothesis that forked tails provide a hydrodynamic advantage over truncate tails at typical cruising speeds. Using experimentally derived pressure fields, we show that the forked tail produces thrust via acceleration reaction forces like the truncate tail during cruising but at increased energetic costs. This reduced efficiency corresponds to differences in the performance of the two tail geometries and body kinematics to maintain similar overall thrust outputs. Our results offer insights into the benefits and tradeoffs of two common fish tail morphologies and shed light on the functional morphology of fish swimming to guide the development of bio-inspired underwater technologies.

Antibacterial activity of seed aqueous extract of Citrus limon (L.) mediated synthesis ZnO NPs: An impact on Zebrafish (Danio rerio) caudal fin development.

Among the different metal oxide nanoparticles, zinc oxide nanoparticles have gained significant importance due to their antibacterial properties against clinically pathogenic bacteria during the organal development. In the present study, biogenic zinc oxide nanoparticles were synthesized using seed extract of Citrus limon by a simple, cost-effective, and green chemistry approach. The synthesized ZnO NPs were characterized by UV-Vis spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, Dynamic Light Scattering, and Scanning Electron Microscopy. Next, the antimicrobial activity of ZnO NPs was tested against clinically pathogenic bacteria, i.e., Pseudomonas fluorescens, Escherichia coli, Enterobacter aerogenes, and Bacillus subtilis. Followed by, ZnO NPs were evaluated for the development of caudal fin in Zebrafish. The UV-Vis spectram result showed a band at 380 nm and FTIR results confirmed the ZnO NPs. The average crystallite size of the ZnO NPs was 52.65 ± 0.5 nm by the Debye Scherrer equation and SEM showed spherical-shaped particles. A zone of inhibition around ZnO NPs applied to P. fluorescens indicates sensitive to ZnO NPs followed by B. subtilis. Among the four different bacterial pathogens, E. aerogenes was the most susceptible compared to the other three pathogens. The calculated sub-lethal concentration of ZnO NPs at 96 h was 153.8 mg/L with a 95% confidence limit ranging from 70.62 to 214.18 mg/L, which was used with partially amputated zebrafish caudal fin growth. A significant (p < 0.5) development (95%) in the amputated caudal fin was detected at 12 days post-amputation. Low concentrated ZnO NPs can reduce developmental malformation. Collectively, suggested results strongly proved that lemon seed-mediated synthesized ZnO NPs had a good pathogenic barrier for bacterial infection during the external organal development for the first time.

The Expression and Function of lincRNA-154324 and the Adjoining Protein-Coding Gene vmp1 in the Caudal Fin Regeneration of Zebrafish.

Caudal fin regeneration is regulated by a variety of mechanisms, but the role of long non-coding RNA (lncRNA) has rarely been studied. The present study aimed to describe the landscape of lncRNAs during caudal fin regeneration using whole transcriptome sequencing, and then to conduct a functional study on the target lncRNAs using real-time fluorescent quantitative PCR (RT-qPCR), in situ hybridization, and the CRISPR/Cas9 method for lncRNA gene knockout. The results of the transcriptome sequencing showed that a total of 381 lncRNAs were differentially expressed, among which ENSDART00000154324 (lincRNA-154324) was found to be highly related to caudal fin regeneration, and thus it was chosen as the target lncRNA for the subsequent functional study. The results regarding the temporal and spatial expression of lincRNA-154324 and the gene knockout results from CRISPR/Cas9 indicated that lincRNA-154324 is involved in the caudal fin regeneration of zebrafish. Importantly, we serendipitously discovered that the cis correlation coefficient between lincRNA-154324 and its neighboring gene vacuole membrane protein 1 (vmp1) is extremely high, and they are essential for the process of caudal fin regeneration. Moreover, studies have found that vmp1 plays an important role in protein secretion, organelle formation, multicellular development, and autophagy. Collectively, our result may provide a framework for the identification and analysis of lncRNAs involved in the regeneration of the zebrafish caudal fin.

Thrust Improvement of a Biomimetic Robotic Fish by Using a Deformable Caudal Fin.

In nature, live fish has various deformable fins which are capable to promote the swimming speed, efficiency, stability, and thrust generation. However, this feature is rarely possessed by current man-made biomimetic robotic fishes. In this paper, a novel deformable caudal fin platform is proposed to improve thrust generation of biomimetic robotic fish. First, the design of the deformable caudal fin is given, which includes a servo motor, a gear-based transmission mechanism, fin bones, and silica membrane. Second, an improved Central Pattern Generator (CPG) model was developed to coordinately control the flapping of the tail and the deformation of the caudal fin. More specifically, three deformation patterns, i.e., conventional nondeformable mode, sinusoidal-based mode, instant mode, of the caudal fin are investigated. Third, extensive experiments are conducted to explore the effects of deformation of the caudal fin on the thrust generation of the biomimetic robotic fish. It was found that the instant mode of the caudal fin has the largest thrust, which sees a 27.5% improvement compared to the conventional nondeformable mode, followed by the sinusoidal-based mode, which also sees an 18.2% improvement. This work provides a novel way to design and control the deformation of the caudal fin, which sheds light on the development of high-performance biomimetic robotic fish.

Hydrodynamic interaction of dorsal fin and caudal fin in swimming tuna.

Tuna, which are known for high-performance swimming, possess a large crescent dorsal fin (DF) and a caudal fin (CF) that differ from those of other fishes. The hydrodynamic interaction between the DF and CF in tuna, which are represented by two tandem 3D flapping plates, is numerically explored in the present study. Hydrodynamic properties and wake structures of the models with and without a DF are compared to investigate the effects of the DF. The thrust on the CF is substantially enhanced by the DF, whereas the force on the DF is not affected by the CF. The constructive interaction between the leading-edge vortex (LEV) on the CF and the vortices shed from the dorsal fin (DFVs) is identified from 3D wake topology and 2D vorticity distributions. The circulation of spanwise vorticity quantitatively reveals that the LEV on the CF is strengthened by the same-signed DFV. The effect of the flapping phase of the CF is examined. The DF-CF interaction is sensitive to the flapping phase at a short spacing, whereas a long spacing between the two fins enables a robust constructive interaction in tuna swimming. A systematic study is carried out to explore the effects of the Strouhal number (St) and the Reynolds number (Re) on the interaction of the fins. The enhancement of thrust due to the DF is diminished at St = 0.63, whereas the Re does not substantially influence the constructive DF-CF interaction.

Platyfish bypass the constraint of the caudal fin ventral identity in teleosts.

BACKGROUND: The caudal fin of teleosts is characterized by dorsoventral symmetry. Despite this external morphology, the principal rays of this appendage connect to bones below the notochord, indicating the ventral (hypochordal) identity of this organ. RESULTS: Here, we report that this typical architecture of the caudal fin is not fully conserved in the platyfish (Xiphophorus maculatus) and the guppy (Poecilia reticulata), representatives of the Poeciliidae family. We show that in these species, 3-4 principal rays connect to bones above the notochord, suggesting an epichordal contribution. Consistently, as examined in platyfish, dorsal identity genes zic1/4 were highly expressed in these rays, providing molecular evidence of their epichordal origin. Developmental analysis revealed that the earliest rays above the notochord emerge at the 10-ray stage of fin morphogenesis. In contrast to zebrafish and medaka, platyfish and guppies display a mirrored shape of dorsal and ventral processes of the caudal endoskeleton. Our study suggests that an ancestral bauplan expanded in poeciliids by advancing its symmetrical pattern. CONCLUSION: The platyfish evolved a fin architecture with the epichordal origin of its upper principal rays and a high level of symmetry in the caudal endoskeleton. This innovative architecture highlights the adaptation of the teleost skeleton.

Coordinated patterning of zebrafish caudal fin symmetry by a central and two peripheral organizers.

BACKGROUND: Caudal fin symmetry characterizes teleosts and likely contributes to their evolutionary success. However, the coordinated development and patterning of skeletal elements establishing external symmetry remains incompletely understood. We explore the spatiotemporal emergence of caudal skeletal elements in zebrafish to consider evolutionary and developmental origins of caudal fin symmetry. RESULTS: Transgenic reporters and skeletal staining reveal that the hypural diastema-defining gap between hypurals 2 and 3 forms early and separates progenitors of two plates of connective tissue. Two sets of central principal rays (CPRs) synchronously, sequentially, and symmetrically emerge around the diastema. The two dorsal- and ventral-most rays (peripheral principal rays, PPRs) arise independently and earlier than adjacent CPRs. Muscle and tendon markers reveal that different muscles attach to CPR and PPR sets. CONCLUSIONS: We propose that caudal fin symmetry originates from a central organizer that establishes the hypural diastema and bidirectionally patterns surrounding tissue into two plates of connective tissue and two mirrored sets of CPRs. Further, two peripheral organizers unidirectionally specify PPRs, forming a symmetric "composite" fin derived from three fields. Distinct CPR and PPR ontogenies may represent developmental modules conferring ray identities, muscle connections, and biomechanical properties. Our model contextualizes mechanistic studies of teleost fin morphological variation.

Regenerating vascular mural cells in zebrafish fin blood vessels are not derived from pre-existing mural cells and differentially require Pdgfrb signalling for their development.

Vascular networks comprise endothelial cells and mural cells, which include pericytes and smooth muscle cells. To elucidate the mechanisms controlling mural cell recruitment during development and tissue regeneration, we studied zebrafish caudal fin arteries. Mural cells colonizing arteries proximal to the body wrapped around them, whereas those in more distal regions extended protrusions along the proximo-distal vascular axis. Both cell populations expressed platelet-derived growth factor receptor ß (pdgfrb) and the smooth muscle cell marker myosin heavy chain 11a (myh11a). Most wrapping cells in proximal locations additionally expressed actin alpha2, smooth muscle (acta2). Loss of Pdgfrb signalling specifically decreased mural cell numbers at the vascular front. Using lineage tracing, we demonstrate that precursor cells located in periarterial regions and expressing Pgdfrb can give rise to mural cells. Studying tissue regeneration, we did not find evidence that newly formed mural cells were derived from pre-existing cells. Together, our findings reveal conserved roles for Pdgfrb signalling in development and regeneration, and suggest a limited capacity of mural cells to self-renew or contribute to other cell types during tissue regeneration.

Understanding the complexity of epimorphic regeneration in zebrafish caudal fin tissue: A transcriptomic and proteomic approach.

The complex epimorphic regeneration of zebrafish caudal fin tissue is hasty and absolute. This study was executed to understand the role of various genes/proteins involved in the regeneration of zebrafish caudal fin tissue through differential transcriptomics and proteomics analysis. Based on our study 1408 genes and 661 proteins were found differentially regulated in the regenerating caudal fin tissue for having at least 1-log fold change. Interleukin, Solute carrier, Protein arginine methyltransferase, Homeobox, Neurotransmitter and several novel genes were found to be associated with regeneration for its differential regulation during the mechanism. Based on the network and pathway analysis the differentially regulated genes and proteins were found allied with activation of cell proliferation, cell viability, cell survival & cell movement and inactivation of organismal death, morbidity, necrosis, death of embryo & cell death. This study has mapped a detailed insight of the genes/proteins expression associated with the epimorphic regeneration more profoundly.

Musculotendinous system of mesopelagic fishes: Stomiiformes (Teleostei).

Every night the greatest migration on Earth starts in the deep pelagic oceans where organisms move up to the meso- and epipelagic to find food and return to the deeper zones during the day. One of the dominant fish taxa undertaking vertical migrations are the dragonfishes (Stomiiformes). However, the functional aspects of locomotion and the architecture of the musculotendinous system (MTS) in these fishes have never been examined. In general, the MTS is organized in segmented blocks of specific three-dimensional 'W-shaped' foldings, the myomeres, separated by thin sheets of connective tissue, the myosepta. Within a myoseptum characteristic intermuscular bones or tendons may be developed. Together with the fins, the MTS forms the functional unit for locomotion in fishes. For this study, microdissections of cleared and double stained specimens of seven stomiiform species (Astronesthes sp., Chauliodus sloani, Malacosteus australis, Eustomias simplex, Polymetme sp., Sigmops elongatus, Argyropelecus affinis) were conducted to investigate their MTS. Soft tissue was investigated non-invasively in E. schmidti using a micro-CT scan of one specimen stained with iodine. Additionally, classical histological serial sections were consulted. The investigated stomiiforms are characterized by the absence of anterior cones in the anteriormost myosepta. These cones are developed in myosepta at the level of the dorsal fin and elongate gradually in more posterior myosepta. In all but one investigated stomiiform taxon the horizontal septum is reduced. The amount of connective tissue in the myosepta is very low anteriorly, but increases gradually with body length. Red musculature overlies laterally the white musculature and exhibits strong tendons in each myomere within the muscle bundles dorsal and ventral to the horizontal midline. The amount of red musculature increases immensely towards the caudal fin. The elongated lateral tendons of the posterior body segments attach in a highly complex pattern on the caudal-fin rays, which indicates that the posterior most myosepta are equipped for a multisegmental force transmission towards the caudal fin. This unique anatomical condition might be essential for steady swimming during diel vertical migrations, when prey is rarely available.

Bioestructura de la piel de la aleta caudal del salmón del atlántico, en estado smolt y sus interacciones con el estado chalimus del Caligus rogercresseyi / Biostructure of the atlantic salmon skin of the caudal fin, in the smolt stage and its interactions with the chalimus stage of Caligus rogercresseyi

RESUMEN: Caligus rogercresseyi es un copépodo que representa uno de los principales desafíos de la industria del cultivo de salmónidos en Chile, ya que afecta profusamente a la piel. Es preciso destacar que los peces en agua dulce y estuario no son afectados, a diferencia del salmón, que desde el post-smolt resulta muy parasitado cuando es trasladado al mar. Se han realizado múltiples estudios sobre el ciclo de vida del parásito y desarrollado tratamientos químicos, físicos y mecánicos para eliminarlos. Sin embargo, a la fecha, los tratamientos no han sido eficaces, lo que produce un problema permanente para el bienestar del animal. El propósito de este estudio fue el de reconocer la bioestructura de la piel de la aleta caudal del salmón del atlántico en los sitios de la interacción con chalimus. Para esto, se utilizaron 15 post-smolt infectados con Caligus y 5 post-smolt controles, sin Caligus. Los salmones fueron aportados por Fundación Chile y la experiencia se realizó en su propio centro experimental. Una vez realizada la eutanasia, mediante sobredosis del anestésico benzocaína, se obtubieron muestras de las aletas caudales, las cuales fueron fijadas en formalina al 10%, incluidas en paraplast para realizar cortes de 5 µm de espesor y teñidas con Tricrómico de Masson y PAS. Los resultados indicaron que la piel de la aleta caudal de los post-smolt afectados presentan mayor altura de la epidermis, escasa células secretoras de mucus y solución de continuidad en la epidermis. Además, la membrana basal se descontinúa y ocurre un aumento de melanomacrófagos en la dermis.

SUMMARY: Caligus rogercresseyi is a copepod that represents one of the main challenges of the salmon farming industry in Chile, since it profusely affects the skin. It should be noted that fish in freshwater and estuaries are not affected, unlike salmon, which from post-smolt is highly parasitized when transferred to the sea. Multiple studies have been carried out on the life cycle of the parasite and chemical, physical and mechanical treatments have been developed to eliminate them. However, to date, the treatments have not been effective, which produces a permanent problem for the welfare of the animal. The purpose of this study was to recognize the biostructure of Atlantic salmon caudal fin skin at sites of interaction with chalimus. For this, 15 post-smolt infected with Caligus and 5 post-smolt controls, without Caligus, were used. The salmon were provided by Fundación Chile and the experience was carried out in its own experimental center. Once the euthanasia was carried out, by means of an overdose of the anesthetic benzocaine, samples of the caudal fins were obtained, which were fixed in 10 % formalin, included in paraplast to make 5 µm-thick sections and stained with Masson's Trichrome and PAS. The results indicated that the skin of the caudal fin of the affected post-smolt presented a greater height of the epidermis, few mucus-secreting cells and a solution of continuity in the epidermis. In addition, the basement membrane is discontinued and an increase in melanomacrophages occurs in the dermis.

New insights into benzo[⍺]pyrene osteotoxicity in zebrafish.

Persistent and ubiquitous organic pollutants, such as the polycyclic aromatic hydrocarbon benzo[⍺]pyrene (BaP), represent a major threat to aquatic organisms and human health. Beside some well-documented adverse effects on the development and reproduction of aquatic organisms, BaP was recently shown to affect fish bone formation and skeletal development through mechanisms that remain poorly understood. In this work, zebrafish bone-related in vivo assays were used to evaluate the osteotoxic effects of BaP during bone development and regeneration. Acute exposure of zebrafish larvae to BaP from 3 to 6 days post-fertilization (dpf) induced a dose-dependent reduction of the opercular bone size and a depletion of osteocalcin-positive cells, indicating an effect on osteoblast maturation. Chronic exposure of zebrafish larvae to BaP from 3 to 30 dpf affected the development of the axial skeleton and increased the incidence and severity of skeletal deformities. In young adults, BaP affected the mineralization of newly formed fin rays and scales, and impaired fin ray patterning and scale shape, through mechanisms that involve an imbalanced bone remodeling. Gene expression analyses indicated that BaP induced the activation of xenobiotic and metabolic pathways, while negatively impacting extracellular matrix formation and organization. Interestingly, BaP exposure positively regulated inflammation markers in larvae and increased the recruitment of neutrophils. A direct interaction between neutrophils and bone extracellular matrix or bone forming cells was observed in vivo, suggesting a role for neutrophils in the mechanisms underlying BaP osteotoxicity. Our work provides novel data on the cellular and molecular players involved in BaP osteotoxicity and brings new insights into a possible role for neutrophils in inflammatory bone reduction.