Caudal Fin Research Articles

A walking fish trace fossil from the early Permian Robledo Mountains Formation of South-Central New Mexico, USA

ABSTRACT A new ichnotaxon, Ambulopisces voigti (ichnogen. et ichnosp. nov.), from the early Permian (Wolfcampian) Robledo Mountains Formation (Hueco Group) of south-central New Mexico, is described and shown to represent a fish walking on a muddy substrate. A. voigti is a compound ichnotaxon comprising alternating left and right pectoral fin impressions that show the walking behaviour plus a superimposed sinusoidal caudal fin drag that can be assigned to Undichna. The pectoral fin impressions are surrounded by expulsion rims, which show that the fins were weight-bearing; these are larger posteriorly where sediment was pushed up by the propulsive motion of the fin. The shape of the expulsion rims thus indicates the direction of travel. Propulsion was accomplished by alternately pressing the pectoral fins into the substrate and flexing the body to bring the opposing pectoral fin and the body forward. The identity of the tracemaker is uncertain, but it was a small, low-profile fish whose pectoral fins spanned only ~ 60 mm. The proximity of the pectoral fin bases to the centerline of the trace does not support a lobe-finned fish as the tracemaker.

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.

Histone lactylation-ROS loop contributes to light exposure-exacerbated neutrophil recruitment in zebrafish

Light serves as a crucial external zeitgeber for maintaining and restoring physiological homeostasis in most organisms. Disrupting of light rhythms often leads to abnormal immune function, characterized by excessive inflammatory responses. However, the underlying regulatory mechanisms behind this phenomenon remain unclear. To address this concern, we use in vivo imaging to establish inflammation models in zebrafish, allowing us to investigate the effects and underlying mechanisms of light disruption on neutrophil recruitment. Our findings reveal that under sustained light conditions (LL), neutrophil recruitment in response to caudal fin injury and otic vesicle inflammation is significantly increased. This is accompanied by elevated levels of histone (H3K18) lactylation and reactive oxygen species (ROS) content. Through ChIP-sequencing and ChIP‒qPCR analysis, we discover that H3K18 lactylation regulates the transcriptional activation of the duox gene, leading to ROS production. In turn, ROS further promote H3K18 lactylation, forming a positive feedback loop. This loop, driven by H3K18 lactylation-ROS, ultimately results in the over recruitment of neutrophils to inflammatory sites in LL conditions. Collectively, our study provides evidence of a mutual loop between histone lactylation and ROS, exacerbating neutrophil recruitment in light disorder conditions, emphasizing the significance of maintaining a proper light-dark cycle to optimize immune function.

A biomechanical study of a polymer material bundled rib fracture fixator.

Rib fractures are one of the most common blunt injuries, accounting for approximately 10% of all trauma patients and 60% of thoracic injuries. Multiple rib fractures, especially flail chest, can cause local chest wall softening due to the loss of rib support, leading to paradoxical breathing, severe pain, and a high likelihood of accompanying lung contusions. This study investigates the mechanical properties of a new polymer material rib internal fixator to provide theoretical data for its clinical use. We conducted in vitro mechanical tests on 20 fresh caudal fin sheep ribs, using different fracture models across four randomly assigned groups (five ribs per group). The fixators were assessed using non-destructive three-point bending, torsion, and unilateral compression tests, with results averaged. Additionally, finite element analysis compared stress and strain in the polymer fixators and titanium alloy rib plates during bending and torsion tests. In vitro tests showed that the polymer fixators handled loads effectively up to a maximum without increase beyond a certain displacement. Bending and torsion tests via finite element analysis showed the polymer material sustained lower maximum equivalent stresses (84.455MPa and 14.426MPa) compared to titanium alloy plates (219.88MPa and 46.47MPa). The polymer rib fixator demonstrated sufficient strength for rib fracture fixation and was superior in stress management compared to titanium alloy plates in both bending and torsion tests, supporting its potential clinical application.

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.

Growth patterns of caudal fin rays are informed by both external signals from the regenerating organ and remembered identity autonomous to the local tissue

Regenerating tissues must remember or interpret their spatial position, using this information to restore original size and patterning. The external skeleton of the zebrafish caudal fin is composed of 18 rays; after any portion of the fin is amputated, position-dependent regenerative growth restores each ray to its original length. We tested for transcriptional differences during regeneration of proximal versus distal tissues and identified 489 genes that differed in proximodistal expression. Thyroid hormone directs multiple aspects of ray patterning along the proximodistal axis, and we identified 364 transcripts showing a proximodistal expression pattern that was dependent on thyroid hormone context. To test what aspects of ray positional identity are directed by extrinsic environental cues versus remembered identity autonomous to the tissue, we transplanted distal portions of rays to proximal environments and evaluated regeneration within the new location. Native regenerating proximal tissue showed robust expression of scpp7, a transcript with thyroid-regulated proximal enrichment; in contrast, regenerating rays originating from transplanted distal tissue showed reduced (distal-like) expression during outgrowth. These distal-to-proximal transplants regenerated far beyond the length of the graft itself, indicating that cues from the proximal environment promoted additional growth. Nonetheless, these transplants initiated regeneration at a much slower rate compared to controls, suggesting memory of distal identity was retained by the transplanted tissue. This early growth retardation caused rays that originated from transplants to grow noticeably shorter than neighboring native rays. While several aspects of fin ray morphology (bifurcation, segment length) were found to be determined by the environment, we found that both regeneration speed and ray length are remembered autonomously by tissues, and that persist through multiple rounds of amputation and regeneration.

Anti-inflammatory effects and beneficial effects of the feed additive Urtica cannabina L. in zebrafish.

Urtica cannabina L. (UL) has been used clinically for centuries because of its anti-inflammatory properties. This study aimed to investigate the underlying mechanisms and anti-inflammatory effects of different UL concentrations in zebrafish. To elucidate UL's anti-inflammatory properties, two inflammation zebrafish models were designed 1) by severing the zebrafish's caudal fin to assess the repairing effect of UL on the tail inflammation, and 2) by inducing lipopolysaccharides (LPS)-mediated intestinal inflammation to assess the protective and reparative effects of UL on intestinal inflammation at the histological and genetic levels. Furthermore, the effect of UL on the LPS-induced intestinal flora changes was also assessed. After caudal fin resection, a scar formed on the tail of the zebrafish, and the area of the caudal fin increased by 1.30 times as much as that of the control group (P < 0.01). Moreover, this tail scar was alleviated after 10 mg/g UL supplementation but not after 30 mg/g UL dose. LPS decreased the feed intake and body weight of the zebrafish; however, these effects were reversed after 10 and 30 mg/g doses of UL. In addition, the LPS treatment also reduced the intestinal goblet cells by 49% in the zebrafish when compared with the control, which was significantly restored after 10 and 30 mg/g UL treatments. At the genetics level, the expression of the pro-inflammatory cytokine genes (TNF-α, IL6, and IL8) showed that 10 and 30 mg/g UL doses could rescue LPS-induced expression. The gut microbiota analysis revealed changes in the abundance of four major bacterial phyla in the 10 and 30 mg/g UL-treated groups, with an increased probiotic Bacteroidota and decreased pathogenic bacteria. These results indicate that UL strongly inhibits inflammation caused by caudal fin removal and LPS-induced inflammatory changes in the zebrafish intensity, suggesting that UL is a feed additive that could be developed to improve resistance to inflammation in livestock.

Lack of Nuclear Localization of the Creb3l1 Transcription Factor Causes Defects in Caudal Fin Bifurcation in Zebrafish Danio rerio.

The formation of normal bone and bone healing requires the cAMP-responsive element binding protein 3-like-1 (Creb3l1) transmembrane transcription factor, as deletion of the murine CREB3L1 results in osteopenic animals with limited capacity to repair bone after a fracture. Creb3l1 undergoes regulated intramembrane proteolysis (RIP) to release the N-terminal transcription activating (TA) fragment that enters the nucleus and regulates the expression of target genes. To expand our understanding of Creb3l1's role in skeletal development and skeletal patterning, we aimed to generate animals expressing only the TA fragment of Creb3l1 lacking the transmembrane domain and thereby not regulated through RIP. However, the CRISPR/Cas9-mediated genome editing in zebrafish Danio rerio caused a frameshift mutation that added 56 random amino acids at the C-terminus of the TA fragment (TA+), making it unable to enter the nucleus. Thus, TA+ does not regulate transcription, and the creb3l1TA+/TA+ fish do not mediate creb3l1-dependent transcription. We document that the creb3l1TA+/TA+ fish exhibit defects in the patterning of caudal fin lepidotrichia, with significantly distalized points of proximal bifurcation and decreased secondary bifurcations. Moreover, using the caudal fin amputation model, we show that creb3l1TA+/TA+ fish have decreased regeneration and that their regenerates replicate the distalization and bifurcation defects observed in intact fins of creb3l1TA+/TA+ animals. These defects correlate with altered expression of the shha and ptch2 components of the Sonic Hedgehog signaling pathway in creb3l1TA+/TA+ regenerates. Together, our results uncover a previously unknown intersection between Creb3l1 and the Sonic Hedgehog pathway and document a novel role of Creb3l1 in tissue patterning.

Short Communication: A novel hypopigmentation for southeast Pacific humpback whales

Southeast Pacific humpback whales (Megaptera novaeangliae) migrate annually to breeding grounds in Machalilla, Ecuador, and Uramba Bahía Málaga, Colombia. This species usually displays a black/ grey body colouration with its dorsal and caudal fins exposed above water. Between 2005 and 2023, whales in these regions were studied and photographed on 1,627 days. Results indicated that 29 whales have novel body markings, including white spots, irregular circles and sinuous lines, which resemble the paintings of 20th Century artist Jackson Pollock. While this novel ‘Pollock‐style’ pigmentation does not appear to cause health problems, we recommend further studies to evaluate its origin and effects.

Disruption of the creb3l1 gene causes defects in caudal fin regeneration and patterning in zebrafish Danio rerio.

The gene cAMP-Responsive Element Binding protein 3-like-1 (CREB3L1) has been implicated in bone development in mice, with CREB3L1 knock-out mice exhibiting fragile bones, and in humans, with CREB3L1 mutations linked to osteogenesis imperfecta. However, the mechanism through which Creb3l1 regulates bone development is not fully understood. To probe the role of Creb3l1 in organismal physiology, we used CRISPR-Cas9 genome editing to generate a Danio rerio (zebrafish) model of Creb3l1 deficiency. In contrast to mammalian phenotypes, the Creb3l1 deficient fish do not display abnormalities in osteogenesis, except for a decrease in the bifurcation pattern of caudal fin. Both, skeletal morphology and overall bone density appear normal in the mutant fish. However, the regeneration of caudal fin postamputation is significantly affected, with decreased overall regenerate and mineralized bone area. Moreover, the mutant fish exhibit a severe patterning defect during regeneration, with a significant decrease in bifurcation complexity of the fin rays and distalization of the bifurcation sites. Analysis of genes implicated in bone development showed aberrant patterning of shha and ptch2 in Creb3l1 deficient fish, linking Creb3l1 with Sonic Hedgehog signaling during fin regeneration. Our results uncover a novel role for Creb3l1 in regulating tissue growth and patterning during regeneration.

A new species of the genus Luciogobius Gill, 1859 (Teleostei, Oxudercidae) from Taiwan.

A new species, Luciogobiusopisthoproctus sp. nov., is described based on 18 specimens collected from Daxi Creek (Yilan) and Babian Creek (Taitung) in Taiwan. The new species is characterized by having a yellowish body with scattered spots on the sides, a black blotch on the caudal fin, the absence of free pectoral-fin rays, and more than 40 vertebrae. The new species can be distinguished from congeners by the following combination of characters: AAA distance (anus to anal-fin origin) shorter than twice the body depth at anus, 4.2-7.2% of standard length (SL); pre-anus length 80.0-92.8% of pre-anal-fin length; snout length 39.7-62.7% of AAA distance; abdominal vertebrae 20-22; caudal vertebrae 20-22; first anal-fin pterygiophore usually inserted behind the second haemal spine.

First record of Telestes pleurobipunctatus (Stephanidis, 1939) in freshwater of Al-Bireh Dam, Wadi Al-Ayoun, Hama, Syria

Despite a large number of studies on freshwater fish fauna in Syrian aquatic habitats lack of data exists for many. This study was conducted in Al-Bireh Dam, located in Wadi Al-Oyoun region, Hama Governorate of Syria and recorded Telestes pleurobipunctatus (Stephanidis, 1939) (Cyprinidae) for the first time. In April 2023, thirteen individuals of the species were caught using local fishing methods. The species is characterised by the presence of a dark band on the sides of the body extending from the front of the snout to the end of the caudal fin, and an orange spot at the base of the pectoral fin. This research sheds light on the qualitative composition of the fish fauna in Al-Bireh Dam Lake, as the species T. pleurobipunctatus is recorded for the first time in Syrian freshwaters.

The effects of light, rearing density, and fish size in culturing juvenile Lumpfish

AbstractObjectiveThere is an impetus for increasing Lumpfish Cyclopterus lumpus hatchery production and rearing efficiency due to the high demand for their usefulness as cleaner fish in salmonid ocean farming. One production bottleneck is the loss of juvenile fish due to aggressive behaviors, including cannibalism. Understanding which factors exacerbate Lumpfish aggression and providing mitigation guidelines to aquaculturists are warranted.MethodsTwo experiments were conducted for an 8‐week period in 2022 in 3‐L aquaria with different juvenile size‐classes (4 and 11 g) subjected to three rearing densities (40, 65, and 90 g/L) under different photoperiod regimes (12 h light : 12 h dark [113 lx]; 24 h light : 0 h dark [21 lx]; and 24 h light : 0 h dark [302 lx]), resulting in nine experimental treatments. Survival, growth, and aggression (occurrence and severity of caudal fin nipping) were evaluated.ResultFor 4‐g Lumpfish, light and density significantly affected growth (weight gain and specific growth rate), while an interaction between light and density significantly affected the occurrence of caudal fin nipping but not the degree of fin nipping or survival. None of the tested variables significantly affected 11‐g fish. Generally, a trend toward increased caudal fin nipping occurred in smaller fish (~45% occurrence in 4‐g fish vs. ~20% in 11‐g fish), indicating that cannibalism may be even greater when Lumpfish are smaller than 4 g but abates as the fish grow.ConclusionOur findings indicate that manipulation of lighting at rearing densities of up to 90 g/L can be used to control growth rates in small Lumpfish, often without resulting in increased fish aggression. For small (~4‐g) Lumpfish, constant low light intensity in combination with a low (40‐g/L) rearing density is recommended for reducing growth and caudal fin nipping. However, as Lumpfish grow, these variables are less effective at manipulating fish growth.

Isolation and characterization of plant-derived exosome-like nanoparticles from Carica papaya L. fruit and their potential as anti-inflammatory agent.

Inflammation is an immune system response that identifies and eliminates foreign material. However, excessive and persistent inflammation could disrupt the healing process. Plant-derived exosome-like nanoparticles (PDENs) are a promising candidate for therapeutic application because they are safe, biodegradable and biocompatible. In this study, papaya PDENs were isolated by a PEG6000-based method and characterized by dynamic light scattering (DLS), transmission Electron Microscopy (TEM), bicinchoninic acid (BCA) assay method, GC-MS analysis, total phenolic content (TPC) analysis, and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. For the in vitro test, we conducted internalization analysis, toxicity assessment, determination of nitrite concentration, and assessed the expression of inflammatory cytokine genes using qRT-PCR in RAW 264.7 cells. For the in vivo test, inflammation was induced by caudal fin amputation followed by analysis of macrophage and neutrophil migration in zebrafish (Danio rerio) larvae. The result showed that papaya PDENs can be well isolated using the optimized differential centrifugation method with the addition of 30 ppm pectolyase, 15% PEG, and 0.2 M NaCl, which exhibited cup-shaped and spherical morphological structure with an average diameter of 168.8±9.62 nm. The papaya PDENs storage is stable in aquabidest and 25 mM trehalose solution at -20˚C until the fourth week. TPC estimation of all papaya PDENs ages did not show a significant change, while the DPPH test exhibited a significant change in the second week. The major compounds contained in Papaya PDENs is 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP). Papaya PDENs can be internalized and is non-cytotoxic to RAW 264.7 cells. Moreover, LPS-induced RAW 264.7 cells treated with papaya PDENs showed a decrease in NO production and downregulation mRNA expression of pro-inflammatory cytokine genes (IL-1B and IL-6) and an upregulation in mRNA expression of anti-inflammatory cytokine gene (IL-10). In addition, in vivo tests conducted on zebrafish treated with PDENs papaya showed inhibition of macrophage and neutrophil cell migration. These findings suggest that PDENs papaya possesses anti-inflammatory properties.

Hydrodynamics of standing-and-walking on the water surface by dolphins using collaborative movements of the body and fins

To break the application scenario limitations of traditional bionic underwater robots and open up the way of information docking between underwater and water surface, a systematic study was conducted on the cross-medium standing-and-walking (SAW) behavior of dolphins under the collaborative movements of the body, caudal, and pectoral fins. A three-dimensional physical model of the biomimetic dolphin robot was established, a collaborative movement law of the body, caudal, and pectoral fins was proposed, and the SAW behavior under two modes, Homologous and Reverse modes, was realized. The mapping relationship between the robot's kinematic parameters and hydrodynamic performance parameters was analyzed, the respective advantages of the two vertical walking modes were compared, and the SAW mechanism of the two modes was revealed physically with the help of the evolution law of the flow field around the robot. The results show that the biomimetic dolphin robot can realize cross-medium SAW behavior through the collaborative movements of the body, caudal pectoral fins. It is worth noting that the Hom mode has a superior walking speed, which can reach up to 0.27 m/s, an increase in 83.3% compared to the Rev mode under the same conditions, while the Rev mode has better walking stability, with a minimum fluctuation rate of 2.59%, a 30.8% improvement compared to the Hom mode. This research provides a novel idea for enhancing the surface operation capability of traditional biomimetic underwater robots and provides an important fluid mechanics theoretical basis for the design of new generation of cross-medium dolphin robots.

A shortfin mako shark circling a finless porpoise with damaged caudal fin.

Research on predator-prey interactions between sharks and cetaceans remain limited. Here, we report on a video of a shortfin mako shark circling a finless porpoise with a damaged caudal fin in the Seto Inland Sea, Japan. The finless porpoise was neither emaciated nor inactive, but unable to swim effectively due to the complete lack of a caudal fin. Some circumstantial evidence, including a bite mark on the porpoise's head, strongly suggests that the mako shark attacked it. Furthermore, the possible time difference between the two injuries the porpoise sustained may reflect the shark's hunting tactics. While mako sharks primarily feed on small fish and cephalopods, this observation suggests they also may prey on live cetaceans more often than previously thought.

Exploring the Effects of Lignin Nanoparticles in Different Zebrafish Inflammatory Models.

Lignin is the most abundant source of aromatic biopolymers and has gained interest in industrial and biomedical applications due to the reported biocompatibility and defense provided against bacterial and fungal pathogens, besides antioxidant and UV-blocking properties. Especially in the form of nanoparticles (NPs), lignin may display also antioxidant and anti-inflammatory activities. To evaluate these characteristics, sonochemically nano-formulated pristine lignin (LigNPs) and enzymatically-phenolated one (PheLigNPs) were used to expose zebrafish embryos, without chorion, at different concentrations. Furthermore, two different zebrafish inflammation models were generated, by injecting Pseudomonas aeruginosa lipopolysaccharide (LPS) and by provoking a wound injury in the embryo caudal fin. The inflammatory process was investigated in both models by qPCR, analyzing the level of genes as il8, il6, il1β, tnfα, nfkbiaa, nfk2, and ccl34a.4, and by the evaluation of neutrophils recruitment, taking advantage of the Sudan Black staining, in the presence or not of LigNPs and PheLigNPs. Finally, the Wnt/β-catenin pathway, related to tissue regeneration, was investigated at the molecular level in embryos wounded and exposed to NPs. The data obtained demonstrated that the lignin-based NPs showed the capacity to induce a positive response during an inflammatory event, increasing the recruitment of cytokines to accelerate their chemotactic function. Moreover, the LigNPs and PheLigNPs have a role in the resolution of wounds, favoring the regeneration process. In this paper, we used zebrafish embryos within 5 days post fertilization (hpf). Despite being an early-stage exemplary, the zebrafish embryos have proven their potential as predicting models. Further long-term experiments in adults will be needed to explore completely the biomedical capabilities of lignin NPs. The results underlined the safety of both NPs tested paved the way for further evaluations to exploit the anti-inflammatory and pro-healing properties of the lignin nanoparticles examined.

Morfometrik Ikan Bileh (Rasbora sp.) dari Perairan Ie Sayang Kabupaten Aceh Barat

Bileh fish (Rasbora sp.) is a fish that lives in freshwater and can be found in the waters of Ie Sayang West Woyla West Aceh District. Excessive exploration has caused the population of bileh fish in nature to decrease and be limited. The first step that needs to be done in aquatic resource management is to identify the type of bileh fish to adopt its cultivation techniques. Fish identification can be done morphologically or molecularly. Morphological identification refers to morphometric studies. This study aims to identify bileh fish species from Ie Sayang waters based on morphometric characteristics. The bileh fish was obtained from community catches in September-November 2023. Morphological identification was done by visualizing and measuring morphometric characters. Data were analyzed descriptively, and the relationship between morphometric characters was analyzed by linear regression. The morphology of bileh fish has a fusiform body shape, terminal mouth type, forked caudal fin, and linea lateralis visible from the operculum to the caudal part. Total length (TL) ranged from 36.94-65.78 mm and standard length (SL) 29.01-52.49 mm. The length-weight correlation of allometric fish was negative. TL characters were closely correlated with SL, HL, DFD, ED, CPD, and VFL.

Skin swabbing protocol to collect DNA samples from small-bodied fish species

Fish species are commonly used as experimental models in the laboratory. DNA is routinely collected from these animals to permit identification of their genotype. The current standard procedure to sample DNA is fin clipping, which involves anaesthetising individuals and removing a portion of the caudal fin. While fin clipping reliably generates good quality DNA samples for downstream applications, there is evidence that it can alter health and welfare, and impact the fish’s behaviour. This in turn can result in greater variation in the data collected. In a recent study we adapted a skin swabbing protocol to collect DNA from small-bodied fish, including sticklebacks and zebrafish, without the use of analgesics, anaesthetics or sharp instruments. A rayon-tipped swab was used to collect mucus from the flank of the fish, which was then used for DNA extraction. We subsequently demonstrated that compared to fin clipping, skin swabbing triggered fewer changes in stress axis activation and behaviour. We also found that gene expression and behaviour data collected from swabbed fish were less variable than similar data collected from fish that had been fin clipped. This potentially allows smaller sample sizes in experimental groups to be used after skin swabbing, thereby reducing animal use. Here we provide a detailed protocol explaining how to collect DNA samples from small laboratory fish using skin swabs.

Okhotsk sculpin Icelus ochotensis (Cottiformes: Cottidae) is a complex; redescription of the type series

The genus Icelus Krøyer, 1845 includes 18 valid species from shelf and upper slope of the northern Pacific, Arctic and North Atlantic. The taxonomy of the genus is under development. To solve taxonomic problems, there is a need to clarify the diagnostic characters of already known species. As it turned out, information about the composition of the type series of the Okhotsk sculpin I. ochotensis Schmidt, 1927 from different sources is contradictory, and the diagnostic characters in the latest revision of the genus and in the keys for species identification diverge from the original description. The work clarifies the composition of the type series of the Okhotsk sculpin from the ZIN collection (36 specimens), provides a redescription and diagnosis; the Lectotype No. 21898 is designated. Icelus ochotensis, characterized by the presence of only two rows of large scales on the body (dorsal row Dl and lateral line Ll), was included in the group “I. bicornis”, along with I. spatula Gilbert et Burke, 1912, I. uncinalis Gilbert et Burke, 1912 and I. stenosomus Andriashev, 1937. Contrary to results of the latest revision of the genus and modern identifying keys, on the top of its head there is not one pair of spines, but two pairs (parietal and nuchal ones), in the form of blunt tubercles hidden in the skin. The dorsal row of scales (Dl) in front is complete (reaches the head); lateral line begins under scales 3rd–4th of the dorsal row and does not extend posteriorly onto caudal fin; scales Ll below the canal pore are immersed in the skin and usually not serrated (one or two tiny spinules may present); supraorbital cirrus (skin appendage) is simple. The urogenital papilla of males is cylindrical, in contrast to the spatulate one in I. spatula. Vertebrae 37–40, D VII–IX 15–19, A 13–16, P 17–18, Ll 38–40, Dl 29–34; axillary scales 6–13. The distribution of the Okhotsk sculpin requires revision, since modern keys for Icelus identification contain incorrect characters for this species (one pair of spines on the top of the head).