Pectoral Fin Research Articles

Human split hand/foot variants are not as functional as wildtype human PRDM1in the rescue of craniofacial defects.

Split hand/foot malformation (SHFM) is a congenital limb disorder presenting with limb anomalies, such as missing, hypoplastic, or fused digits, and often craniofacial defects, including a cleft lip/palate, microdontia, micrognathia, or maxillary hypoplasia. We previously identified three novel variants in the transcription factor, PRDM1, that are associated with SHFM phenotypes. One individual also presented with a high arch palate. Studies in vertebrates indicate that PRDM1 is important for development of the skull; however, prior to our study, human variants in PRDM1 had not been associated with craniofacial anomalies. Using transient mRNA overexpression assays in prdm1a-/- mutant zebrafish, we tested whether the PRDM1 SHFM variants were functional and could lead to a rescue of the craniofacial defects observed in prdm1a-/- mutants. We also mined previously published CUT&RUN and RNA-seq datasets that sorted EGFP-positive cells from a Tg(Mmu:Prx1-EGFP) transgenic line that labels the pectoral fin, pharyngeal arches, and dorsal part of the head to examine Prdm1a binding and the effect of Prdm1a loss on craniofacial genes. The prdm1a-/- mutants exhibit craniofacial defects including a hypoplastic neurocranium, a loss of posterior ceratobranchial arches, a shorter palatoquadrate, and an inverted ceratohyal. Injection of wildtype (WT) hPRDM1 in prdm1a-/- mutants partially rescues the palatoquadrate phenotype. However, injection of each of the three SHFM variants fails to rescue this skeletal defect. Loss of prdm1a leads to a decreased expression of important craniofacial genes by RNA-seq, including emilin3a, confirmed by hybridization chain reaction expression. Other genes including dlx5a/dlx6a, hand2, sox9b, col2a1a, and hoxb genes are also reduced. Validation by real-time quantitative PCR in the anterior half of zebrafish embryos failed to confirm the expression changes suggesting that the differences are enriched in prx1 expressing cells. These data suggest that the three SHFM variants are likely not functional and may be associated with the craniofacial defects observed in the humans. Finally, they demonstrate how Prdm1a can directly bind and regulate genes involved in craniofacial development.

Effect of Active–Passive Deformation on the Thrust by the Pectoral Fins of Bionic Manta Robot

Effect of Active–Passive Deformation on the Thrust by the Pectoral Fins of Bionic Manta Robot

Aliphatic hydrocarbons in fin spines of adult sturgeon (Acipenser stellatus) and their relationship with potentially toxic elements in the northern and southern regions of the Caspian Sea

Currently, the pollution of the Caspian Sea by the oil industry is one of the highest problems in this area. Critically endangered species inhabit this sea, such as sturgeons, whose ecological value is incalculable. Thus, we aimed to evaluate the level of contamination of aliphatic hydrocarbons of petroleum and its relation with several toxic elements directly on sturgeons spines. A total of 40 adult starry sturgeons (Acipenser stellatus) were obtained within a repopulation programme in the northern and southern coastal waters of the Caspian Sea. The marginal pectoral fin was extracted from each fish to determine aliphatic hydrocarbons, arsenic, cadmium, mercury, nickel, lead, and vanadium. Subsequently, the sturgeons were released. Clearly, the presence of hydrocarbons was evidenced in all the sampled areas finding higher concentrations in the northern areas (N1 = 1.35 ± 0.4; N2 = 1.65 ± 0.46; N3 = 1.27 ± 0.40; S1 = 0.61 ± 0.22; S2 = 0.85 ± 0.43 mg/kg). Furthermore, to a greater or lesser extent, some toxic elements, mainly Hg and As, have been linked to aliphatic hydrocarbons.

Analyses of fin ray types to detect strontium markers in juvenile blunt-snout bream Megalobrama amblycephala

BackgroundRestocking by introducing hatchery-reared fish into wild habitats aids in the restoration of fishery aquatic ecosystems and reefs to increase the abundance of fish resources, restore the ecological balance of water bodies, and enhance ecosystem functioning. Accurately, rapidly, and effectively evaluating the success of restocking using chemical markers (e.g., strontium [Sr]) remains challenging for fisheries management. Consequently, for non-lethal fish sampling, hard tissues, such as fin rays, have received increasing attention as a target for marking method. However, data on the differences in marking different types of fin rays remain limited. Therefore, we exposed juvenile blunt snout bream individuals (Megalobrama amblycephala) to 0 (control group) or 800 mg/L of SrCl2·6H2O (marked group) for 5 days and transferred them into normal aerated water for post-immersion culture. We sampled their pectoral, dorsal, ventral, anal, and caudal fin rays. The Sr marks among the fin types were sampled at 0 and 20 days post-immersion and evaluated using an electron probe micro-analyzer (EPMA) for the five-day Sr/Ca ratios, along with line transect and Sr mapping analyses.ResultsSr marking signatures were observed in all fin types in the marked group, with a success rate of up to 100%. Although marking efficiency varied among the different fin ray types, the highest Sr/Ca ratios were most often detected in the dorsal fin. Cross-sectional Sr concentration maps of all fin rays sampled showed high-Sr domains in the marked group; in contrast, the entire cross-sections of the control group displayed low Sr contents, indicating successful marking efficiency.ConclusionsFin ray Sr marking is a successful method for juvenile M. amblycephala, with the advantages of non-lethality and negligible sampling injuries, facilitating the rapid and effective evaluation of Sr marking in restocking M. amblycephala.

Cis-regulatory control of mammalian Trps1 gene expression.

TRPS1 serves as the causative gene for tricho-rhino phalangeal syndrome, known for its craniofacial and skeletal abnormalities. The Trps1 gene encodes a protein that represses Wnt signaling through strong interactions with Wnt signaling inhibitors. The identification of genomic cis-acting regulatory sequences governing Trps1 expression is crucial for understanding its role in embryogenesis. Nevertheless, to date, no investigations have been conducted concerning these aspects of Trps1.To identify deeply conserved noncoding elements (CNEs) within the Trps1 locus, we employed a comparative genomics approach, utilizing slowly evolving fish such as coelacanth and spotted gar. These analyses resulted in the identification of eight CNEs in the intronic region of the Trps1 gene. Functional characterization of these CNEs in zebrafish revealed their regulatory potential in various tissues, including pectoral fins, heart, and pharyngeal arches. RNA in-situ hybridization experiments revealed concordance between the reporter expression pattern induced by the identified set of CNEs and the spatial expression pattern of the trps1 gene in zebrafish. Comparative in vivo data from zebrafish and mice for CNE7/hs919 revealed conserved functions of these enhancers. Each of these eight CNEs was further investigated in cell line-based reporter assays, revealing their repressive potential. Taken together, in vivo and in vitro assays suggest a context-dependent dual functionality for the identified set of Trps1-associated CNE enhancers.This functionally characterized set of CNE-enhancers will contribute to a more comprehensive understanding of the developmental roles of Trps1 and can aid in the identification of noncoding DNA variants associated with human diseases.

Propulsion curve analysis and optimisation of biomimetic pectoral fin with three degree of freedom based on multi-layer perception

This paper aims to improve the swimming efficiency of biomimetic robotic fish by optimising its propulsion curve with three degree of freedom (DOF), in which the key is to minimise the resistance during swing backstroke of the pectoral fin. For this purpose, a reference point on the pectoral fin is first selected, and then an 8-shaped propulsion curve is constructed to coordinate rowing and flapping motions. Meanwhile, a propulsion curve of feathering motion is also given correspondingly. On this basis, the overall curvature and curve offset are proposed as measurement parameters for the deformation of the propulsion curve and the proportion of abdominal/dorsal circles in the propulsion curve, respectively. As the motion law of feathering is given in a sinusoidal pattern, a data set of hydrodynamic parameters is obtained for pectoral fin propulsion under different motion parameter conditions by computational fluid dynamics(CFD) numerical simulation. Once again, a propulsion curve optimisation model is established based on multi-layer perception(MLP), which uses the hydrodynamic parameters data set as input. The results show that the resistance of swing backstroke reached the minimum when overall curvature is π/10 and curve offset is 0.4, which is enhanced by 30.13% and 33.33% at thrust and lift direction compared to the existing design, respectively. Furthermore, the flow field structure and hydrodynamic parameters around the robotic fish are calculated by CFD. The results show that two sets of vortex rings are generated around the fish body during a propulsion cycle. The vortex rings detached towards the lower and upper sides of the fish body such that the lift is minimal, the thrust direction is relatively stable, and the resistance is minimal during the swing backstroke. The experimental results indicate that it can raise propulsion efficiency during the pectoral fin propulsion process, verifying the effectiveness of this method.

Differential accumulation of metals in the lacustrine and fluvial Alpine bullheads (Cottus poecilopus) and recovery of fish from metal contamination after a flash flood

The spatiotemporal distribution and transport of mercury, zinc, molybdenum, rubidium, and strontium from alpine terrestrial ecosystems to alpine lake and mountain stream populations of Cottus poecilopus were investigated. Metals were measured for 66 wild fish collected from different lakes and Javorinka stream across. Mercury was measured in the pectoral fins, other elements in the skull. Bullheads contained more metals in the alpine lakes than in the mountain stream. In particular, mercury and zinc concentrations in lake bullheads were 6 and 2.5 times higher, respectively, than those of stream-dwelling fish. New data were generated on metal bioaccumulation in fish of understudied West Carpathian alpine lake environments. In July 2018, a major flood occurred in the area of the Javorinka. Already then, the mercury content in bullheads increased significantly. Bioaccumulation of mercury in fish occurred very quickly after the flood and was also significant in the following 2019. Then, the concentrations of mercury quickly decreased up to 70% in 2021–2022. Average concentrations of molybdenum and rubidium in bullheads in the stream rapidly declined in the year following the flood disturbance, but within less than 2 years, the metal levels stabilized at about the same level as in 2017 prior the flood. Strontium concentrations in fish dropped rapidly immediately after the flood, increased in the following years, and dropped again after 4 years, suggesting that many more factors are influencing strontium bioaccumulation in fish that are comparable in magnitude to the flood. The most serious warning seems to be the absence of biogenic zinc. The average concentration in the Alpine bullheads population in the stream has declined by 70% in less than 5 years and is steadily declining. An important result of this study is the demonstration that disturbance by a single factor (heavy rainfall and flooding) has a clear and timely effect on average metal concentrations in the fish population.Graphical abstract

A NEW MOORISH IDOL (TELEOSTEI, ZANCLIDAE) FROM THE EOCENE OF BOLCA, ITALY

The acanthuriform family Zanclidae, whose members are commonly known as moorish idols, has until now been comprised of two species, the extant Zanclus cornutus and the Eocene Eozanclus brevirostris. Herein, a new moorish idol, Angiolinia mirabilis n. gen. et sp., is described based on three specimens from the Eocene Pesciara site of the Bolca locality, northern Italy. Morphologically, Angiolinia mirabilis n. gen. et sp. appears to be intermediate between Eozanclus brevirostris and Zanclus cornutus and differs from them by having the following features: body depth 85–87% SL; head length 38.3–39.2% SL; third dorsal-fin spine reaching about 50% SL; pectoral disc width 23.2% SL; dorsal fin containing 31 or 32 rays; anal fin containing 26 or 27 rays; pectoral fin with 11 or 12 moderately elongate rays and caudal fin truncate. A comparative osteological analysis suggests that the family Zanclidae is defined by two morphological features, namely the presence of a broadly expanded and anteroventrally convex cleithrum forming the so-called pectoral disc together with the coracoid and having a large number of dorsal- and anal-fin rays. The Eocene acanthuriform Massalongius gazolai from Bolca represents the sister group to the Zanclidae. Within the zanclids, Eozanclus brevirostris represents the sister group to the pair formed by Angiolinia mirabilis n. gen. et sp. and Zanclus cornutus. This clade is supported by the shared possession of a single supernumerary spine on the first dorsal-fin pterygiophore, a single uroneural in the caudal skeleton, and all but the first two dorsal-fin spines distally filamentous.

A Rigid-Flexible Coupling Dynamic Model for Robotic Manta with Flexible Pectoral Fins

The manta ray, exemplifying an agile swimming mode identified as the median and paired fin (MPF) mode, inspired the development of underwater robots. Robotic manta typically comprises a central rigid body and flexible pectoral fins. Flexible fins provide excellent maneuverability. However, due to the complexity of material mechanics and hydrodynamics, its dynamics are rarely studied, which is crucial for the advanced control of robotic manta (such as trajectory tracking, obstacle avoidance, etc.). In this paper, we develop a multibody dynamic model for our novel manta robot by introducing a pseudo-rigid body (PRB) model to consider passive deformation in the spanwise direction of the pectoral fins while avoiding intricate modeling. In addressing the rigid-flexible coupling dynamics between flexible fins and the actuation mechanism, we employ a sequential coupling technique commonly used in fluid-structure interaction (FSI) problems. Numerical examples are provided to validate the MPF mode and demonstrate the effectiveness of the dynamic model. We show that our model performs well in the rigid-flexible coupling analysis of the manta robot. In addition to the straight-swimming scenario, we elucidate the viability of tailoring turning gaits through systematic variations in input parameters. Moreover, compared with finite element and CFD methods, the PRB method has high computational efficiency in rigid-flexible coupling problems. Its potential for real-time computation opens up possibilities for future model-based control.

A comparative study of three modes for realizing transmedia standing-and-hovering behavior in robotic dolphins

Three different hovering modes, namely, the caudal fin, pectoral fins, and multi fins, were utilized to achieve the standing-and-hovering behavior in robotic dolphins. A three-dimensional dolphin model, consisting of body, caudal fin, and symmetric pectoral fins, was used as the virtual swimmer to implement three hovering modes. A novel paddling motion was proposed, and a symmetric shape was designed of the pectoral fins. The hovering mechanisms of different modes were revealed, and the mapping relationships between different motion and performance parameters such as hovering height, efficiency, stability, and rapidity were established. The respective advantages of the three hovering modes were compared. The results showed that the caudal fin mode had the best hovering stability, while the pectoral fins mode had the best hovering rapidity. Moreover, it is worth noting that the multi fins mode had both the good hovering stability and rapidity. Therefore, the optimal hovering mode and motion parameters can be selected based on different expected objectives to achieve the best results. This study provides a new approach to break through the spatial barriers to movement of underwater robots and provides a solid hydrodynamic theoretical basis for the development of cross-medium robots with multiple hovering modes.

Precision of four calcified structures for age estimation of Black Carp

AbstractObjectiveBlack Carp Mylopharyngodon piceus is an emerging invasive species in North America with an expanding population in the Mississippi River basin. Current aging methods use a suite of structures for age estimation, and a single structure is needed to minimize processing time, to maximize consistency of age and growth measurements, and to allow for back‐calculation of individual fish length at age.MethodsIn total, 236 Black Carp were collected throughout the year from 2017 to 2019 through incidental captures by commercial fishers and biologists. In a subsample, 119 Black Carp from 429 to 1268 mm total length were compared for the precision of annuli counts by two experienced readers for the two anterior pectoral fin rays, the anterior dorsal fin ray, sectioned vertebrae, and lapilli otoliths based on percent exact agreement (PA), percent agreement within 1 year (PA ± 1), coefficient of variation (CV), and bubble plots. Consensus annuli counts were compared by PA and CV between structures. We applied annuli counts, as opposed to age, as fish were collected during all seasons and structures were examined independently by readers without knowledge of capture date.ResultVertebrae and dorsal rays had the highest PA between readers. Dorsal ray had the lowest CV and higher PA ± 1. Pectoral rays and lapilli otoliths had the lowest PA. Between‐structure consensus annuli counts indicated that pectoral rays and the dorsal ray annuli counts were the most similar (PA >70% and CV <12) and lapilli otoliths were the most dissimilar (PA >35% and CV >24). Reader‐reported confidence was highest for vertebrae, then in decreasing order, dorsal ray, pectoral rays, and lapilli otoliths. Lumens were present in all fin rays with only minor effects observed on annuli counts, aside from the anterior‐most pectoral fin ray, in which lumens obscured the presence of one or more potential annuli in 61% of structures.ConclusionThe dorsal ray had the highest agreement between readers, with agreement with ±1 year at 98%; the structure can be efficiently extracted and processed, and the structure's morphology and growth pattern are conducive to aging older fish. Vertebrae had high agreement between readers, but a systematic pattern of double bands in vertebrae increased the between‐reader variation in older fish as the interannual growth pattern compressed the viewable area; this was identified by readers based on aging criteria and highlights the need for training novice readers. Validation of annual growth in the tested suite of structures is still needed.

Hydrodynamic analysis of fin–fin interactions in two-manta-ray schooling in the vertical plane

This study investigates the interaction of a two-manta-ray school using computational fluid dynamics simulations. The baseline case consists of two in-phase undulating three-dimensional manta models arranged in a stacked configuration. Various vertical stacked and streamwise staggered configurations are studied by altering the locations of the top manta in the upstream and downstream directions. Additionally, phase differences between the two mantas are considered. Simulations are conducted using an in-house developed incompressible flow solver with an immersed boundary method. The results reveal that the follower will significantly benefit from the upstroke vortices (UVs) and downstroke vortices depending on its streamwise separation. We find that placing the top manta 0.5 body length (BL) downstream of the bottom manta optimizes its utilization of UVs from the bottom manta, facilitating the formation of leading-edge vortices (LEVs) on the top manta’s pectoral fins during the downstroke. This LEV strengthening mechanism, in turn, generates a forward suction force on the follower that results in a 72% higher cycle-averaged thrust than a solitary swimmer. This benefit harvested from UVs can be further improved by adjusting the phase of the top follower. By applying a phase difference of π/3 to the top manta, the follower not only benefits from the UVs of the bottom manta but also leverages the auxiliary vortices during the upstroke, leading to stronger tip vortices and a more pronounced forward suction force. The newfound interaction observed in schooling studies offers significant insights that can aid in the development of robot formations inspired by manta rays.

Streptococcus agalactiae Associated with "Dark Body" Disease on Snakeskin Gourami Farmed in the Mekong Delta, Vietnam

Streptococcosis, due to Streptococcus agalactiae, has become a serious challenge for aquaculture around the world. Therefore, the main purpose of this work was to confirm the etiological agent that caused "dark body" disease in snakeskin gourami (Trichogaster pectoralis) cultured in the Mekong Delta, Vietnam. Infected fish displayed clinical signs, including anorexia, lethargic swimming on the water surface, corneal opacity, and hemorrhage in the base of the fin. Remarkably, abnormal black coloration on the body and serious hemorrhage at the base of the pectoral fin, and on the body were found in infected fish. In total, 75 bacterial strains were isolated from different diseased fish farms. Based on morphological and physiological characteristics, the API 20 Strep test, and 16S rRNA sequence analysis, the result illustrated that the bacterial isolates were identified as S. agalactiae. Additionally, antibiotic sensitivity testing revealed that all the S. agalactiae isolates were sensitive to amoxicillin, rifampicin, clarithromycin, erythromycin, doxycycline, cephalexin, novobiocin, and sulfamethoxazole-trimethoprim. Interestingly, S. agalactiae strains were only resistant to gentamycin in this study. Two strains, SRT41 and SRT43, carried out an experimental challenge with concentrations from 104 to 107 CFU/ml in healthy snakeskin gourami, and the LD50 values of the isolates, SRĐT41 and SRĐT43, were determined to be 2.15 × 105 and 3.59 × 103 CFU/ml, respectively, after 7 days. To our knowledge, this is the first report of S. agalactiae derived from intensively cultured snakeskin gourami in the Mekong Delta, Vietnam.

Contact Exchanges in Bottlenose Dolphin Mother–Calf Pairs

The relationship between a dolphin mother and her calf has been well studied, but details regarding tactile exchanges within these dyads are limited. Contacts between five adult female bottlenose dolphins (Tursiops truncatus) and their calves, with data from three pairs analyzed statistically, were examined from video collected in October 2017, 2018, 2019, and in January 2018. Of 289 contact events, calves initiated 65.7% (n = 190), of which 82.6% (n = 157) were affiliative; 77.8% (n = 77) of mother-initiated contacts were categorized similarly. Thus, the overall trend for mother–calf contacts was affiliative. Mothers initiated contact with the dorsal fin less often (n = 3), while calves initiated with their dorsal fin more often (n = 40), especially one-year-old (C1) calves (n = 33). The body was used to initiate contact more by three-year-old (C3) calves (n = 47) and less by C1 calves (n = 22). Both results are likely an artifact of the infant position used by calves at different developmental stages. Only two-year-old (C2) calves initiated agonistic contact with their rostrum (n = 4); 75% of these contacts were initiated by one male calf. Mothers used the body to initiate contact with most calf ages, though contact by pectoral fin occurred more often than expected with their C2 calves (n = 11). Since 72.7% of these contacts came from one mother, a specific maternal style may be present. Only one mother used her rostrum with her C3 calf to initiate agonistic contacts; all others used the fluke. Several variables, including individual preference, calf sex, and maternal experience, may explain some of the contact patterns, but a larger sample size is needed to illustrate potential patterns among pairs. Still, these results support the notion that mother–calf dyads share more affiliative than agonistic contacts, expanding our knowledge on the tactile relationships of mother–calf pairs.

Isolation, identification, and monoclonal antibody development of largemouth bass virus

Largemouth bass virus (LMBV) poses a significant threat to largemouth bass farming, leading to substantial economic losses. In December 2022, massive largemouth bass juveniles died at a fish farm in the city of Xinxiang, China. Through a series of experiments, we conclusively identified LMBV as the causative pathogen. The affected fish displayed anorexia, lethargy, and hemorrhage at the pectoral and caudal fin base. No parasites or pathogenic bacteria were detected on the body surface or gills, or isolated from the diseased fish. Severe hemorrhage, lymphocyte infiltration, and extensive necrosis were observed in the liver, spleen, intestine, and stomach of the moribund fish. The tissue homogenate from the diseased fish induced epithelioma papulosum cyprini cells (EPC) cell death, while no such effects were observed in grouper spleen (GS) cells. Sequence similarity analysis of the major capsid protein (MCP) indicated the virus shared 100% similarity with the LMBV-FS2021 strain, placing it within the Ranavirus genus. Transmission electron microscopy (TEM) observations revealed plenty of hexagonal virions accumulated in the cytoplasm of infected EPC cells. Artificial infection demonstrated that LMBV-XX01 was highly fatal to Micropterus salmoides juveniles, with an LD50 of 103.081 TCID50/fish. RT-qPCR detection confirmed that LMBV appeared in all sampled tissues of the challenged largemouth bass, with significantly higher viral loads detected in the liver and heart compared to other tissues. Additionally, we successfully obtained a highly purified recombinant MCP of LMBV and developed two strains of monoclonal antibodies targeting MCP of LMBV-XX01. Overall, our findings provide valuable materials and insights for the design of prevention strategies and the development of detection methods for LMBV.

New species of the eel genera Dysomma and Dysommina from Vietnam, South China Sea (Anguilliformes: Synaphobranchidae).

Two new cutthroat eel species are described from Vietnam. Dysomma intermedium sp. nov. has a relatively long trunk, being about half of head length and anal-fin origin more than twice pectoral-fin length behind the pectoral-fin tip; pectoral fin well developed; dorsal-fin origin over or slightly in front of base of pectoral fin; two intermaxillary teeth; four or five compound teeth on ethmovomer; single row of seven or eight teeth on lower jaw; total lateral-line pores 70-76; and 21 pre-anal and 118-124 total vertebrae. Dysommina brevis sp. nov. differs from congeners by having a trunk shorter than head length, its length 11.1%-11.8% TL; a short pre-anal length 24.6%-25.6% TL, eye diameter 11.8%-12.3% head length; three large and one or two small teeth on ethmovomer; and fewer teeth on the upper and lower jaws. In addition, a specimen representing the first record of Dysommina orientalis in Vietnamese water is documented.

Fish can use coordinated fin motions to recapture their own vortex wake energy.

During swimming, many fishes use pectoral fins for propulsion and, in the process, move substantial amounts of water rearward. However, the effect that this upstream wake has on the caudal fin remains largely unexplored. By coordinating motions of the caudal fin with the pectoral fins, fishes have the potential to create constructive flow interactions which may act to partially recapture the upstream energy lost in the pectoral fin wake. Using experimentally derived velocity and pressure fields for the silver mojarra (Eucinostomus argenteus), we show that pectoral-caudal fin (PCF) coordination enables the circulation and interception of pectoral fin wake vortices by the caudal fin. This acts to transfer energy to the caudal fin and enhance its hydrodynamic efficiency at swimming speeds where this behaviour occurs. We also find that mojarras commonly use PCF coordination in nature. The results offer new insights into the evolutionary drivers and behavioural plasticity of fish swimming as well as for developing more capable bioinspired underwater vehicles.

Early ontogenetic development of Cynodon gibbus (Characiformes: Cynodontidae) in the Amazon River basin

Abstract Knowledge regarding the early life history of neotropical fish, although incipient, is crucial for the accurate identification of larvae collected from the natural environment. Such details are important for defining spawning, drift, and nursery areas as well as the reproductive periods of species. Herein, the larval development of Cynodon gibbus was described using morphological, meristic, and morphometric characteristics. Specimens were collected from open water limnetic zones and under macrophyte stands in the Amazon basin from 2010 to 2023. Forty-eight larvae with standard lengths ranging from 5.73 to 21.57 mm were studied. The larvae have a long to very long body, small eyes, and a small head, which progresses to a moderate size in the preflexion stage. Furthermore, the larvae had ample mouths with numerous conical teeth, an oval-triangular swim bladder, overlapping dorsal and anal fins, and the tip of the pectoral fin not reaching the swim bladder. Pigmentation pattern comprised two punctate pigments above the fontanelle, the rectum, and at the lower and upper ends of the caudal peduncle. Various body parts exhibited predominant allometric relationships, reflecting differential developmental rates among them in response to fundamental ecological requirements for survival. The C. gibbus larvae can be identified by a combination of the position of dorsal, anal and pectoral fins, pigmentation pattern, swim bladder shape, and the total number of myomeres (51 to 53).

Two new species of freshwater goby (Teleostei, Gobiidae) from the Upper Youshui River, Chongqing, China.

Two previously unknown species of Rhinogobius have been discovered in the streams of the Upper Youshui River, within the Yuan River Basin, Xiushan County, Chongqing, China. These new species are named as Rhinogobiussudoccidentalis and Rhinogobiuslithopolychroma. Phylogenetic analysis based on mitochondrial genomes revealed that R.sudoccidentalis is genetically closest to R.reticulatus, while R.lithopolychroma shares the greatest genetic similarity with R.leavelli. Morphological distinctions allow for the clear differentiation of these species. Rhinogobiussudoccidentalis sp. nov. is characterized by having VI-VII rays in the first dorsal fin and I, 8-9 rays in the second dorsal fin. The longitudinal scale series typically consists of 22-24 scales, while the transverse scale series comprises 7-8 scales. Notably, the predorsal scale series is absent and the total vertebrae count is 12+17=29. Rhinogobiuslithopolychroma sp. nov. can be distinguished from other species by the presence of 13-15 rays on the pectoral fin. Its longitudinal scale series ranges from 30 to 33 scales, with no scales in the predorsal area. The total vertebral count is 30, with 12 precaudal and 18 caudal vertebrae. The head and body of this species are light gray with irregular orange markings on the cheeks and opercle. Through morphological and molecular analyses, it has been confirmed that R.lithopolychroma and R.sudoccidentalis represent novel species within the Rhinogobius genus.

Gymnocranius indicus, a new large-eye seabream from the Indian Ocean

Abstract Gymnocranius indicus sp. nov. is described as a new species of the fish subfamily Monotaxinae (Sparoidea: Lethrinidae), a group of commercially important species distributed throughout the Indo-West Pacific, on the basis of 16 specimens collected from the Indian Ocean. The new species shares the following characters with its western Pacific sibling, the eyebrowed large-eye seabream, G. superciliosus: elongate body, distinctive and conspicuous dark patch above the eye, prominent forehead, moderately forked caudal fin, its lobes slightly convex inside, flank silvery, and reddish-to-red dorsal, pectoral, anal and caudal fins. However, principal component analysis based on seven morphological variables distinguished most specimens from the Indian Ocean from G. superciliosus. The most influential variable in the analysis was the eye diameter, significantly larger in the new species than in G. superciliosus. All specimens of the new species that were examined also lacked blue ornamentation on the snout and cheek. At the mitochondrial cytochrome oxidase subunit-I locus, the mean genetic p-distance between the two species was 0.039. With Gymnocranius indicus sp. nov., the genus now includes 12 valid nominal species; three additional species remain undescribed.