Swim Bladder Research Articles

Triplophysa wulongensis, a new species of cave-dwelling loach (Teleostei, Nemacheilidae) from Chongqing, Southwest China.

We describe a new species of cave-dwelling loach, Triplophysa wulongensissp. nov., based on specimens collected in a subterranean pool in a cave in Wulong County, Chongqing, Southwest China. The pool is connected to the Wujiang River drainage. Triplophysa wulongensis differs from its congeners by the following combination of characters: eyes present, caudal fin with 18 branched rays; posterior chamber of the air bladder degenerate; stomach U-shaped; intestine without bends or loops immediately posterior to stomach; body smooth and scaleless, and lateral line complete. The mitochondrial cytochrome b sequence differs from those of other published sequences of species of Triplophysa by 14.9–24.9% in K2P distance. Phylogenetic analysis based on cytochrome b gene sequences recovered T. wulongensis as sister taxon to all other cave-dwelling species of Triplophysa.

Mycobacteriosis in cultured koi carp Cyprinus carpio caused by Mycobacterium paragordonae and two Mycolicibacterium spp.

Mycobacteriosis has caused economic losses in fish production of koi carp in Japan since 1981. In this study, we performed histopathological analyses, bacterial identification and challenge test for characterization of mycobacteriosis in koi carp. Spontaneously diseased koi carp externally showing lethargy and emaciation with pin-head body shape were obtained from culture ponds in Niigata, Japan. We isolated bacteria on 1% Ogawa medium at 30 °C and obtained 14 mycobacterial isolates. Chromogenicity, growth rate and biochemical properties were analyzed using the bacterial isolates. Phylogenetic analyses using 16S rRNA and RpoB-HSP65 concatenated sequence were also performed with Neighbor-Joining method. To fulfil the Koch's postulates, common carp were challenged with five representative isolates. Among the visceral organs, the peritoneal fibroplasia accompanied many macrophage aggregations were observed in the diseased fish. Granulomas consisted of central macrophages with melanin pigment were found in the trunk kidney of the diseased fish. Ziehl-Neelsen positive bacilli were detected in mesentery of the posterior chamber of the swim bladder and in the trunk kidney. The bacterial isolates were classified into three groups based on the colony morphology: yellow/smooth colonies (Y/S-isolates), white/rough colonies (W/R-isolate), and white/smooth colonies (W/S-isolates). The results in biochemical tests and phylogenetic analyses revealed that Y/S-isolates were identified as M. paragordonae. W/R- and W/S-isolates were classified into rapid-growing mycobacterium (Runyon IV) based on the morphological and biochemical characteristics. Although W/R- and W/S-isolates were not identified in species level, the former was closely related to Mycolicibacterium peregrinum and the latter was classified into Mycolicibacterium smegmatis clade in the phylogenetic tree for 16S rRNA. The cumulative mortality of fish challenged with Y/S-, W/R- and W/S-isolates were 30%–50% in 100 days post-infection and the dead fish showed the typical symptoms. These data revealed that mycobacteriosis of koi carp cultured in Japan was caused by several mycobacterial species including M. paragordonae and two unidentified Mycolicibacterium spp.

First Record of Pseudotolithus senegallus (Cuvier, 1830) in the Mediterranean Sea

This article firstly records Pseudotolithus senegallus (Cuvier, 1830) species in the Mediterranean Sea. juvenile specimen of Pseudotolithus senegallus (Cuvier, 1830) with total length 15.5 cm and total weight 37 g, was obtained by experimental bottom trawling using commercial bottom trawler (stretched mesh size: 15 mm; duration time: four hours; location: east of Suez Canal main stream in the Mediterranean, off Port Said). Opercle lining jet black, showing through a dark blotch externally. Axils of pectoral-fin base dark, distal portion of caudal fin darkish whereas anal and pelvic fins are yellowish. Gas bladder with a pair of arborescent appendages, dividing into short anterior branches and a dozen or so long tubular posterior appendages along sides of bladder beyond its tip. I suggest the method of introduction to the Mediterranean waters is ballast water of ships as it is recorded only from Mauritania to Angola on the western coast of Africa.

Gene co-expression network analysis reveals mechanisms underlying ozone-induced carbamazepine toxicity in zebrafish (Danio rerio) embryos

Sewage effluent ozonation can reduce concentrations of chemical pollutants including pharmaceutical residues. However, the formation of potentially toxic ozonation byproducts (OBPs) is a matter of concern. This study sought to elucidate toxicity mechanisms of ozonated carbamazepine (CBZ), an anti-epileptic drug frequently detected in sewage effluents and surface water, in zebrafish embryos (Danio rerio). Embryos were exposed to ozonated and non-ozonated CBZ from 3 h post-fertilization (hpf) until 144 hpf. Embryotoxicity endpoints (proportion of dead and malformed embryos) were assessed at 24, 48, and 144 hpf. Heart rate was recorded at 48 hpf. Exposure to ozonated CBZ gave rise to cardiovascular-related malformations and reduced heart rate. Moreover, embryo-larvae exposed to ozonated CBZ displayed a lack of swim bladder inflation. Hence, the expression patterns of CBZ target genes involved in cardiovascular and embryonal development were investigated through a stepwise gene co-expression analysis approach. Two co-expression networks and their upstream transcription regulators were identified, offering mechanistic explanations for the observed toxicity phenotypes. The study presents a novel application of gene co-expression analysis elucidating potential toxicity mechanisms of an ozonated pharmaceutical with environmental relevance. The resulting data was used to establish a putative adverse outcome pathway (AOP).

Embryotoxicity of Five Cytostatics in Fathead Minnow (Pimephales promelas) Larvae.

Cytostatics are compounds used in chemotherapy, known to be genotoxic, mutagenic, and teratogenic at low concentrations. The amount of cytostatic drugs prescribed increases every year as does their release into the aquatic ecosystems, which possibly is a major concern for the health of aquatic organisms. This study aimed to evaluate the putative toxicity of five cytostatics to fathead minnow (Pimephales promelas) larvae: tamoxifen, capecitabine, methotrexate, cyclophosphamide, and ifosfamide. Eggs collected post-fertilization were exposed for 6days to a range of concentrations, including one above environmental level. At all environmental concentrations, no significant difference in mortality, hatching time, length, heart rate, and presence of malformations were found. Altogether, these cytostatics donotseem embryotoxicto fish. Although, an increased proportion of complete swim bladder were found after ifosfamide's exposure, suggesting an interaction with the thyroid axis, involved in swim bladder development. Complementary work should address other endpoints, such as behavioral changes, reproductive success, and transgenerational effects.

Does the bowfin gas bladder represent an intermediate stage during the lung-to-gas bladder evolutionary transition?

Whether phenotypic evolution occurs gradually through time has prompted the search for intermediate forms between the ancestral and derived states of morphological features, especially when there appears to be a discontinuous origin. The gas bladder, a derived character of the Actinopteri, is a modification of lungs, which characterize the common ancestor of bony vertebrates. While gas bladders and lungs are similar in many ways, the key morphological difference between these organs is the direction of budding from the foregut during development; essentially, the gas bladder buds dorsally and the lungs bud ventrally from the foregut. Did the shift from ventral lungs to dorsal gas bladder transition through a lateral-budding stage? To answer this question, the precise location of budding during gas bladder development in bowfin, representing the sister lineage to teleosts, has been debated. In the early 20th-century, it was suggested that the bowfin gas bladder buds laterally from the right wall of the foregut. We used nano-CT scanning to visualize the early development of the bowfin gas bladder to verify the historical studies of gas bladder developmental morphology and determine whether the direction of gas bladder budding in bowfin could be intermediate between ventrally budding lungs and dorsally budding gas bladders. We found that the bowfin gas bladder buds dorsally from the anterior foregut; however, during early development, the posterior gas bladder twists right. As development progresses, the posterior, right-hand twist becomes shallower, and the gas bladder itself shifts toward a mid-dorsal position. The budding site is definitively dorsal, despite the temporary lateral twist of the posterior gas bladder.

Molecular detection of the swim bladder parasite Anguillicola crassus (Nematoda) in fecal samples of the endangered European eel Anguilla anguilla

The European eel Anguilla anguilla is listed as critically endangered by the IUCN. Among many threats, the introduced parasitic nematode Anguillicola crassus is suspected to alter the eels' swim bladder and jeopardize their reproductive oceanic migration. To date, gaining knowledge about the distribution and prevalence of A. crassus requires individual sacrifice (over 50,000 eels were sacrificed for epidemiology studies since 2010). This paper describes a non-lethal molecular protocol for identifying prevalence of A. crassus in A. anguilla, based on searching for A. crassus DNA in the feces of eels. Tests using three DNA microsatellite markers specific to the nematode showed that molecular detection provided similar results to visual examination of the swim bladder in up to 80% of the cases, and allowed for comparison of prevalence among sites. Easy to implement, this non-lethal protocol for detecting A. crassus could be valuable for management plans of this endangered species.

Inhibition of swim bladder inflation in Japanese medaka (Oryzias latipes) embryos following exposure to select pharmaceuticals alone and in combination

This study leveraged the Japanese medaka fish embryo model for the assessment of effects of select contaminants on early development in fish. Fish embryos were exposed to various pharmaceutical contaminants including synthetic hormones and non-steroidal anti-inflammatory drugs and their effects on development were observed. Initial screening determined that swim bladder inflation failure was the most common endpoint detected. Swim bladder inflation failure was first explored in a study demonstrating that medaka require access to the air-water interphase to inflate their swim bladders in a time-dependent manner, and swim bladder inflation failure was correlated with mortality. Fish embryos were exposed 24-hours post fertilization until hatch to concentration ranges of various pharmaceutical contaminants including: 17β-estradiol, 17α-ethinylestradiol, and levonorgestrel (1 to 1000 µg/L), or diclofenac (0.32 to 100 mg/L). The main effect observed across all four compounds was a significant increase in failure of swim bladder inflation with increasing exposure concentration (24 to 72-hours post-hatch). Following single compound experiments combinatorial exposures using no-observed-effect concentrations were conducted. The main effect observed was a significant decrease in inflation success 24-hours post-hatch following a binary mixture of levonorgestrel and 17α-ethinylestradiol, as well as a significant decrease in swim bladder inflation success at all times following exposure to a quaternary mixture of all four compounds. This study demonstrated that embryonic exposure to pharmaceutical compounds, both alone and in combination, resulted in failure of swim bladder inflation in larval Japanese medaka.

Developing coral trout, Plectropomus leopardus larviculture technology: application of floating skimmer

Coral trout Plectopomus leopardus seed production has not been established well compared to other popular groupers such as tiger and hybrid grouper. Thus, the research has been focusing on the protocol construction of larviculture to improve survival and productivity. This study aimed to evaluate the application of floating skimmer to encourage swim bladder inflation in order to increase survival. Coral trout eggs were stocked in 5,000 L concrete tanks. Rotifer fed started on Day 2 (D2) afternoon and copepods nauplii on D4. Oil was dropped on the rearing water surface from D1 to D5 for without application of floating skimmer (control) and to D3 for with the application. A floating skimmer was installed on the surface of rearing water from D3 afternoons to D10. The survival rate was determined on D50. The results showed that application floating skimmer had a significantly higher survival rate (6.18±1.4 %) than without application (5.28±1.64%) (p<0.05). Observation under a microscope confirmed that swim bladder inflation first noticed on D4. The application of floating skimmer promoted a higher swim bladder inflation rate than without skimmer. From an economical aspect, application of skimmer in coral trout larviculture resulted in higher profit.

BIMODAL OXYGEN UPTAKE OF FRESHWATER AIR-BREATHING FEATHERBACK, NOTOPTERUS NOTOPTERUS (PALLAS)

Oxygen uptake through gills and the swim bladder in relation to body weight have been measured in Notopterus notopterus at 24.5±1.0 oC, using closed glass respirometer. With increase in body weight from 4.90 to 90.00 g, the rate of oxygen uptake per unit time (ml O 2 h -1 ) increased from 1.520 to 4.113, 0.994 to 3.033 and 2.514 to 7.146 mlO 2 h -1 through air, water and air+water respectively. The slope ‘b’ of the regression line for oxygen uptake per unit time in relation to body weight from air, water and total (air+water) were found to be 0.318, 0.403 and 0.350 respectively. The relationship has been found highly significant. The weight specific oxygen consumption in relation to body weight mlO 2 kg -1 h -1 from air, water and air + water decreased from 309.750 to 45.700, 202.825 to 33.770 and 512.575 to 79.400 mlO 2 kg –1 h –1 respectively with gradual increase in the body weight from 4.90 to 90.00 g. The log-log plot between the two variables gave straight lines with the slope ‘b’ of-0.618, -0.597 and-0.649 through air, water and air+water respectively. It has been estimated that a N. notopterus having average body weight of 29.01 g, extracted about 63% of oxygen from aerial route while only 37% through its aquatic route. Key words : Air-breathing fish, Notopterus notopterus , bimodal oxygen uptake

Mutual adaptations between hosts and parasites determine stress levels in eels.

Invasive parasites may severely affect their new hosts. Two invasive parasites occurring in the European eel (Anguilla anguilla) are the Asian swim bladder nematode Anguillicola crassus and the Ponto-caspian acanthocephalan Pomphorhynchus sp., which were introduced to the river Rhine in the early 1980/90s. The Japanese eel (Anguilla japonica), as the native host of A. crassus, developed mutual adaptations to the swim bladder parasite, which are lacking in the European eel. Therefore, after its spread to Europe, infestations of European eels with A. crassus were found to be more severe and caused massive swim bladder wall damages mainly due to the feeding activity of the adult nematodes. A suppression of the immune system also appears to be likely, which allows secondary infections e.g. by bacteria or other parasites in European eels. Acanthocephalans of the genus Pomphorhynchus have not been described so far in Japanese eels, in contrast to European eels, which regularly show infestations with Pomphorhynchus sp. By using these differentially adapted host-parasite associations for experimental studies, host stress responses were examined in the present study in relation to the degree of mutual adaptations between eel hosts and parasites.Under laboratory conditions, Japanese and European eels were each inoculated with A. crassus and Pomphorhynchus sp., respectively, to investigate their stress responses against differently adapted parasites. The stress response was determined by analyzing plasma levels of cortisol, which is the main corticosteroid hormone during stress response of fish. The results show a strong cortisol release in European eels after infestation with A. crassus whereas Japanese eels only react against Pomphorhynchus sp. infestations. These results are consistent with the initial hypothesis that a low degree of host-parasite adaptations lead to stronger host stress responses against the parasite.

First highlight of sound production in the glassy sweeper Pempheris schomburgkii (Pempheridae)

Many sounds produced by fishes remain to be described. Understanding sound production for vocal species would permit the development of passive acoustic monitoring of fish diversity. The present study investigated sound production in the glassy sweeper Pempheris schomburgkii in Guadeloupe reefs, French West Indies. Two recording approaches were used: passive acoustic monitoring in the wild and active recordings with hand-held individuals in captivity. Calls consisted of series of harmonic pop sounds with a dominant frequency of 360 Hz. On coral reefs, they were produced in chorus, starting after sunset and lasting up to 3 h. Sounds recorded in situ were longer with more pulses than sounds recorded from captive specimens. These differences in temporal features suggest two types of sounds: acoustic signals that act as distress calls and those that might be involved in group-level activities such as group cohesion and reproduction. A morphological study was also performed to describe the anatomy of the sound production apparatus which consisted of a pair of large sonic muscles which inserted dorsally on a contractible anterior part of the swim bladder. Contractions of these muscles extend rostrally this part of the swim bladder while an inner sheet of elastic connective tissue acts as a recoiling system to help the swim bladder recover its initial position during relaxation of the sonic muscles. The present results, therefore, contribute to the description of sound production by fishes found in an underexplored region and further illustrate how passive acoustics may be used to monitor fish populations in the future.

Why does illegal wildlife trade persist in spite of legal alternatives in transboundary regions?

ABSTRACT Both the characteristics of the value chains and the social-ecological context within which they exist are important to uncover motivations for engagement in legal and illegal value chains. Bêche-de-mer (dried sea cucumbers), shark fins, and fish maw (dried swim bladders) are valued products in the South Fly region of Papua New Guinea (PNG). We applied value chain analysis (VCA) to map the ‘vertical’ characteristics of trade and ‘horizontal’ contextual issues driving the trade. Vertical VCA showed that both legal and illegal value chains end in the same Asian cities, but using different routes. Prices offered by illegal middlemen to PNG fishers were significantly lower than those offered by legal buyers. Horizontal analysis showed five drivers (lack of information, obligatory dependencies to middlemen, kinship ties, need for cash, inaccessibility of legal markets) for accepting lower prices. We recommend interventions necessary to tackle these systemic drivers of illegal trade.

Tracing the genetic footprints of vertebrate landing in non-teleost ray-finned fishes

Rich fossil evidence suggests that many traits and functions related to terrestrial evolution were present long before the ancestor of lobe- and ray-finned fishes. Here, we present genome sequences of the bichir, paddlefish, bowfin, and alligator gar, covering all major early divergent lineages of ray-finned fishes. Our analyses show that these species exhibit many mosaic genomic features of lobe- and ray-finned fishes. In particular, many regulatory elements for limb development are present in these fishes, supporting the hypothesis that the relevant ancestral regulation networks emerged before the origin of tetrapods. Transcriptome analyses confirm the homology between the lung and swim bladder and reveal the presence of functional lung-related genes in early ray-finned fishes. Furthermore, we functionally validate the essential role of a jawed vertebrate highly conserved element for cardiovascular development. Our results imply the ancestors of jawed vertebrates already had the potential gene networks for cardio-respiratory systems supporting air breathing.

Morphology and composition of Goldeye (Hiodontidae; Hiodon alosoides) otoliths

We provide up-to-date morphological and compositional data on otoliths of the osteoglossomorph Goldeye (Hiodon alosoides). Using computed tomography (CT) X-ray, we documented the location of each of the three pairs of otoliths (lapilli, sagittae, and asterisci) in relation to the swim bladder, which extended forward in close proximity to the sagittae and asterisci. The lappili were the largest otoliths in terms of surface area and volume, but the sagittae were highly modified, appearing spiral in shape when viewed dorsally, with a surface area to volume ratio more than double that of the lapilli. Using scanning electron microscopy, the surface of each otolith was viewable in great detail, and small otoconia (~10.5 μm diameter) were observed on each, but were most numerous on the sagittae. On scanning electron micrographs, the sagittae appeared to be bi-lobed, with asymmetrical lobes each oriented in the same general direction. Using neutron and X-ray diffraction methods, we found three polymorphs of calcium carbonate crystals (aragonite, vaterite, and calcite), sometimes all within the same otolith. However, in general, lapilli and sagittae were composed predominately of aragonite whereas asterisci were composed chiefly of vaterite. With these results, we provide information on a unique species, whose inclusion in future studies would benefit our understanding of fish hearing, fish evolution, and fisheries ecology.

Effects of dietary selenium on growth performance, antioxidative status and tissue selenium deposition of juvenile Chu's croaker (Nibea coibor)

Selenium (Se) is an essential antioxidative trace element for animals. Proper dietary Se supplementation could promote growth and antioxidative ability of fish species, especially for those under oxidative stress caused by high-density aquaculture model. However, the narrow safety rage between deficiency and toxicity doses of Se complicates its use for supplementation purpose. Here, we reported the effects of dietary Se supplementation with sodium selenite (0.21, 0.53, 0.79, 1.11, 1.45 and 1.72 mg Se/kg diet, P1–P6) on the growth performance, antioxidative status and tissue Se deposition of an important marine economic fish, Chu's croaker (Nibea coibor). After an 8-week feeding trial, it was demonstrated that the dietary Se supplementation (P1–P3) significantly improved the weight gain of the fish, while a decreased trend of weight gain was observed at higher Se supplementation levels (P4–P6). The activities of glutathione peroxidase (GPx) in serum and liver significantly increased with the increasing Se levels. While, the activities of superoxide dismutase (SOD) and catalase (CAT) firstly increased and then decreased with the increasing Se levels, with highest value presented in P4 and P3 group, respectively. The trends of malondialdehyde (MDA) content in serum and liver were opposite to those of CAT, with lowest value in P3 group. Similar to their enzyme activity counterparts, the mRNA expression of GPx1, SOD1 and SOD2 in liver were also significantly affected by the dietary Se levels. Furthermore, it was shown that Se contents in liver, muscle and swim bladder linearly increased with the dietary Se levels, with the Se accumulation efficiency of liver > muscle > swim bladder. It can be concluded that a dietary Se supplementation of 0.74 mg/kg is suggested for the aquaculture of juvenile N. coibor, based on the weight gain, antioxidative enzyme activities/expression and tissue Se accumulation.

1H NMR based metabolomic profiling of early life stage zebrafish (Danio rerio) exposed to a water-soluble fraction of weathered sediment-bound diluted bitumen

Spills of diluted bitumen (dilbit) from pipelines pose a risk to the health of aquatic organisms, including fish, and with expected increases in production and transportation of dilbit, these risks could increase. To date, the majority of studies have investigated effects of fresh dilbit on aquatic organisms, but little is known about effects of weathered sediment-bound dilbit, including mechanisms of toxicity. The goal of this study was to use 1H NMR based metabolomics to identify altered metabolites and pathways in early life-stages of zebrafish (Danio rerio) exposed to a sediment derived water-soluble fraction of dilbit (SDWSF) to better understand mechanisms of adverse effects. Zebrafish embryos exposed to the SDWSF until 120 h post-fertilization exhibited increased prevalence of pericardial edema, yolk sac edema, and swim bladder malformations that are typical of exposure to fresh dilbit. Concentrations of nine metabolites (alanine, glutamine, lysine, threonine, tyrosine, betaine, taurine, inosine, and glycerol) were significantly altered in embryos exposed to SDWSF. Pathway topology analysis revealed four potentially impacted pathways: 1) phenylalanine, tyrosine, and tryptophan biosynthesis, 2) taurine and hypotaurine metabolism, 3) alanine, aspartate, and glutamate metabolism, and 4) glycine, serine, and threonine metabolism. Altered metabolites were linked to several biological process, that when perturbed could be key events in mechanisms of developmental effects observed in embryos. Future studies should further investigate the role of perturbations to these metabolites and pathways to determine the specific role they might play in adverse effects of exposure to dilbit.

Revision of the diagnostic characters of two morphologically similar snook species, Centropomus viridis and C. nigrescens (Carangiformes: Centropomidae).

Historically, the taxonomic identification of the two snook species, Centropomus viridis and C. nigrescens, has been challenging due to their morphological similarity and the inconsistency of the characters used for diagnosis. Therefore, this study aimed to evaluate the usefulness of the morphologic, meristic, and morphometric characters currently being used to identify C. viridis and C. nigrescens, based on molecular data. The results showed that the gas-bladder shape (i.e., C. viridis with diverticula and C. nigrescens without diverticula) was the only morphological character univocally related to genetic identification. Likewise, geometric morphometrics separated two groups; each corresponds to only one of two genetically (and gas bladder shape) identified species. Of all the meristic characters examined, only the second dorsal fin ray count (nine for C. viridis and ten for C. nigrescens) was related to the gas bladder shape and genetic identity; therefore, it is the only external character with a diagnostic utility to separate each species.

Kualitas Kolagen Gelembung Renang Ikan Gulamah (Johnius trachycephalus) Dari Perairan Pesisir Kota Tarakan

Gulamah fish is a bycatch that is commonly found in the waters of the City of Tarakan. Gulamah fish in Tarakan City is processed into salted fish which produces offal waste and swimming bubbles. Swimming bubbles are known to have high collagen content. The purpose of this study was to obtain information about the length relationship between fish weight and swim bladder as well as the collagen characteristics of the gulamah swim bladder. The research was conducted in 2 stages, namely the length-weight analysis stage with swimming bubbles, and the second stage, namely the extraction and characterization of collagen from the swimming bladder of gulamah fish. The relationship between fish length and weight is a positive allometric, while the relationship between fish length and fish weight and swimming bladder of fish is a negative allometry. The physical chemical parameters of collagen obtained water content values of 29.28% - 29.30%, protein 2.86% - 2.88%, fat 9.53% - 9.55% and viscosity 11.5 ?sp.Gulamah fish is a bycatch that is commonly found in the waters of the City of Tarakan. Gulamah fish in Tarakan City is processed into salted fish which produces offal waste and swimming bubbles. Swimming bubbles are known to have high collagen content. The purpose of this study was to obtain information about the length relationship between fish weight and swim bladder as well as the collagen characteristics of the gulamah swim bladder. The research was conducted in 2 stages, namely the length-weight analysis stage with swimming bubbles, and the second stage, namely the extraction and characterization of collagen from the swimming bladder of gulamah fish. The relationship between fish length and weight is a positive allometric, while the relationship between fish length and fish weight and swimming bladder of fish is a negative allometry. The physical chemical parameters of collagen obtained water content values of 29.28% - 29.30%, protein 2.86% - 2.88%, fat 9.53% - 9.55% and viscosity 11.5 ?sp.

Comparative Transcriptome Analysis During the Seven Developmental Stages of Channel Catfish (Ictalurus punctatus) and Tra Catfish (Pangasianodon hypophthalmus) Provides Novel Insights for Terrestrial Adaptation.

Tra catfish (Pangasianodon hypophthalmus), also known as striped catfish, is a facultative air-breather that uses its swim bladder as an air-breathing organ (ABO). A related species in the same order (Siluriformes), channel catfish (Ictalurus punctatus), does not possess an ABO and thus cannot breathe in the air. Tra and channel catfish serve as great comparative models for investigating possible genetic underpinnings of aquatic to land transitions, as well as for understanding genes that are crucial for the development of the swim bladder and the function of air-breathing in tra catfish. In this study, hypoxia challenge and microtomy experiments collectively revealed critical time points for the development of the air-breathing function and swim bladder in tra catfish. Seven developmental stages in tra catfish were selected for RNA-seq analysis based on their transition to a stage that could live at 0 ppm oxygen. More than 587 million sequencing clean reads were generated, and a total of 21,448 unique genes were detected. A comparative genomic analysis between channel catfish and tra catfish revealed 76 genes that were present in tra catfish, but absent from channel catfish. In order to further narrow down the list of these candidate genes, gene expression analysis was performed for these tra catfish-specific genes. Fourteen genes were inferred to be important for air-breathing. Of these, HRG, GRP, and CX3CL1 were identified to be the most likely genes related to air-breathing ability in tra catfish. This study provides a foundational data resource for functional genomic studies in air-breathing function in tra catfish and sheds light on the adaptation of aquatic organisms to the terrestrial environment.