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The identification and expression of germ cells are important for studying sex-related mechanisms in fish. The vasa gene, encoding an ATP-dependent RNA helicase, is recognized as a molecular marker of germ cells and plays a crucial role in germ cell development. Silurus asotus, an important freshwater economic fish species in China, shows significant sex dimorphism with the female growing faster than the male. However, the molecular mechanisms underlying these sex differences especially involving in the vasa gene in this fish remain poorly understood. In this work, the vasa gene sequence of S. asotus (named as Savasa) was obtained through RT-PCR and rapid amplification of cDNA end (RACE), and its expression in embryos and tissues was analyzed using qRT-PCR and an in situ hybridization method. Letrozole (LT) treatment on the larvae fish was also conducted to investigate its influence on the gene. The results revealed that the open reading frame (ORF) of Savasa was 1989 bp, encoding 662 amino acids. The SaVasa protein contains 10 conserved domains unique to the DEAD-box protein family, showing the highest sequence identity of 95.92% with that of Silurus meridionalis. In embryos, Savasa is highly expressed from the two-cell stage to the blastula stage in early embryos, with a gradually decreasing trend from the gastrula stage to the heart-beating stage. Furthermore, Savasa was initially detected at the end of the cleavage furrow during the two-cell stage, later condensing into four symmetrical cell clusters with embryonic development. At the gastrula stage, Savasa-positive cells increased and began to migrate towards the dorsal side of the embryo. In tissues, Savasa is predominantly expressed in the ovaries, with almost no or lower expression in other detected tissues. Moreover, Savasa was expressed in phase I–V oocytes in the ovaries, as well as in spermatogonia and spermatocytes in the testis, implying a specific expression pattern of germ cells. In addition, LT significantly upregulated the expression of Savasa in a concentration-dependent manner during the key gonadal differentiation period of the fish. Notably, at 120 dph after LT treatment, Savasa expression was the lowest in the testis and ovary of the high concentration group. Collectively, findings from gene structure, protein sequence, phylogenetic analysis, RNA expression patterns, and response to LT suggest that Savasa is maternally inherited with conserved features, serving as a potential marker gene for germ cells in S.asotus, and might participate in LT-induced early embryonic development and gonadal development processes of the fish. This would provide a basis for further research on the application of germ cell markers and the molecular mechanisms of sex differences in S. asotus. [ABSTRACT FROM AUTHOR]

Since the closure of fishing in the Yangtze River, the population of ferocious fish in Poyang Lake has been steadily increasing. In order to investigate whether the Predatory activity of ferocious fish impact the population of Procambarus clarkii, we employed Silurus asotus and Channa argus as predators, using eight different types of bait organisms in this study. Three sizes of P. clarkii larvae (small: 39.20±1.30 mm; medium: 49.82±2.13 mm; large: 58.99±1.16 mm), along with Cyprinus carpio, Carassius auratu, Squaliobarbus curriculus, Mosquitofish, Hypoph-thalmichthys molitrix, Pseudorasbora parva and Macrobrachium nipponense, were used as prey to examine the species selectivity of S. asotus and C. argus and the size selectivity of P. clarkii larvae. The results revealed that: (1) S. asotus and C. argus exhibited a preference for nocturnal predation, with their peak predation occurring between 20:00--8:00; (2) In the presence of various food organisms simultaneously, S. asotus and C. argus did not prey on P. clarkii larvae, displaying clear predation preference for C. carpio, mosquitofish and M. nipponense. (3) When presented with P. clarkii larvae of the same size, S. asotus exhibited a pronounced predation preference for small size P. clarkii larvae, while C. argus preyed significantly more on small-sized P. clarkii larvae than on large-sized ones (P<0.05). (4) In the equal polyculture combination of various sizes of P. clarkii larvae, both S. asotus and C. argus displayed a clear preference for small size P. clarkii larvae, and this preference intensified with increasing size gap among the P. clarkii larvae. In summary, when multiple food organisms coexist, P. clarkii is not the preferred prey for ferocious fish, however, when the variety and quantity of other food organisms are limited, smaller-sized P. clarkii larvae remain at a high risk of predation. [ABSTRACT FROM AUTHOR]

Simple Summary: Procambarus clarkii is typically viewed as a predator rather than prey, due to its strong anti-predatory capabilities. However, during its juvenile stage, it remains vulnerable to predators. Nonetheless, complex outdoor habitats can offer some protection. By examining the effects of three different types of shelters with various coverages and combinations on the predation rhythm, behavior, and efficiency of Silurus asotus on juvenile Procambarus clarkii, we found that the presence and complexity of shelters in the environment have a limited impact on the predatory activities of Silurus asotus. Among the shelter types, PVC pipes offered the best protection, followed by stone, with water grass providing the least protection. Furthermore, the protective effect of shelters increased with coverage rate. Therefore, we suggest that the type and abundance of shelters significantly influence the predation rhythm and behavior of Silurus asotus on Procambarus clarkii in outdoor environments. Procambarus clarkii is adept at using natural shelters and caves to evade attacks from predators. However, the concealment abilities and mechanisms of P. clarkii for different types of shelters under predation pressure have not yet been reported. In this study, laboratory experiments were carried out to determine the effects of different coverages (25%, 50%, and 75%) and different combinations (I–VII) of three types of shelters (PVC pipes, water grass, and stone) on the predation rhythm, behavior, and abilities of Silurus asotus on P. clarkii. The results indicated that the predation of S. asotus on P. clarkii exhibited significant rhythmicity under shelter conditions, excluding PVC pipes, 75% stone, and combination VI. Among the three types of shelters, PVC pipes provided the strongest concealment, followed by stone and water grass. With the increase in shelter coverage, the anti-predation ability of P. clarkii continued to increase, and the optimal shade rate for water grass was 50%. In the different shelter combinations, the environmental complexity had little effect on the predation activity of S. asotus on P. clarkii. These findings demonstrated that the type and abundance of shelters in the wild environment can affect the predation rhythm and activities of S. asotus on P. clarkii. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the growth performance of far eastern catfish (Silurus asotus) on outdoor fish farms to obtain basic data for the domestic eastern catfish aquaculture industry. An outdoor fish farm was directly monitored from June 2018 to October 2019 to determine the farming conditions, growth performance, and water quality. The growth performance in 2017 was analyzed using data from the same fish farm. Three years of monitoring showed that the fish farm required approximately 5–6 months between stocking, harvesting, and selling an S. asotus batch. The growth parameters, namely, the weight gain rate (WGR), specific growth rate (SGR) for culture periods, SGR for feeding periods, and feed coefficient rate (FCR), were 4,664.7%, 1.27%, 2.43%, and 1.25 in 2017; 6,452.0%, 1.52%, 2.79%, and 1.42 in 2018; and 3,270.0%, 1.11%, 2.12%, and 1.38 in 2019, respectively. Moreover, the WGR was two-fold higher in 2018 than 2019, whereas the FCR was more effective in 2019 than 2018, presumably because of the stocking density. No mass mortality was observed during the water quality analysis. The results of this study provide basic data for the development of the catfish industry.

Copyright of South China Fisheries Science is the property of South China Fisheries Science Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The identification and expression of germ cells are important for studying sex-related mechanisms in fish. The vasa gene, encoding an ATP-dependent RNA helicase, is recognized as a molecular marker of germ cells and plays a crucial role in germ cell development. Silurus asotus, an important freshwater economic fish species in China, shows significant sex dimorphism with the female growing faster than the male. However, the molecular mechanisms underlying these sex differences especially involving in the vasa gene in this fish remain poorly understood. In this work, the vasa gene sequence of S. asotus (named as Savasa) was obtained through RT-PCR and rapid amplification of cDNA end (RACE), and its expression in embryos and tissues was analyzed using qRT-PCR and an in situ hybridization method. Letrozole (LT) treatment on the larvae fish was also conducted to investigate its influence on the gene. The results revealed that the open reading frame (ORF) of Savasa was 1989 bp, encoding 662 amino acids. The SaVasa protein contains 10 conserved domains unique to the DEAD-box protein family, showing the highest sequence identity of 95.92% with that of Silurus meridionalis. In embryos, Savasa is highly expressed from the two-cell stage to the blastula stage in early embryos, with a gradually decreasing trend from the gastrula stage to the heart-beating stage. Furthermore, Savasa was initially detected at the end of the cleavage furrow during the two-cell stage, later condensing into four symmetrical cell clusters with embryonic development. At the gastrula stage, Savasa-positive cells increased and began to migrate towards the dorsal side of the embryo. In tissues, Savasa is predominantly expressed in the ovaries, with almost no or lower expression in other detected tissues. Moreover, Savasa was expressed in phase I–V oocytes in the ovaries, as well as in spermatogonia and spermatocytes in the testis, implying a specific expression pattern of germ cells. In addition, LT significantly upregulated the expression of Savasa in a concentration-dependent manner during the key gonadal differentiation period of the fish. Notably, at 120 dph after LT treatment, Savasa expression was the lowest in the testis and ovary of the high concentration group. Collectively, findings from gene structure, protein sequence, phylogenetic analysis, RNA expression patterns, and response to LT suggest that Savasa is maternally inherited with conserved features, serving as a potential marker gene for germ cells in S.asotus, and might participate in LT-induced early embryonic development and gonadal development processes of the fish. This would provide a basis for further research on the application of germ cell markers and the molecular mechanisms of sex differences in S. asotus.

Procambarus clarkii is adept at using natural shelters and caves to evade attacks from predators. However, the concealment abilities and mechanisms of P. clarkii for different types of shelters under predation pressure have not yet been reported. In this study, laboratory experiments were carried out to determine the effects of different coverages (25%, 50%, and 75%) and different combinations (I–VII) of three types of shelters (PVC pipes, water grass, and stone) on the predation rhythm, behavior, and abilities of Silurus asotus on P. clarkii. The results indicated that the predation of S. asotus on P. clarkii exhibited significant rhythmicity under shelter conditions, excluding PVC pipes, 75% stone, and combination VI. Among the three types of shelters, PVC pipes provided the strongest concealment, followed by stone and water grass. With the increase in shelter coverage, the anti-predation ability of P. clarkii continued to increase, and the optimal shade rate for water grass was 50%. In the different shelter combinations, the environmental complexity had little effect on the predation activity of S. asotus on P. clarkii. These findings demonstrated that the type and abundance of shelters in the wild environment can affect the predation rhythm and activities of S. asotus on P. clarkii.

Copyright of Journal of Food Safety & Quality is the property of Journal of Food Safety & Quality Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The east Asian catfish Silurus asotus is a common species living in fresh water in Japan. The complete mitochondrial genome of the S. asotus from Lake Biwa in Japan was analyzed using next-generation sequencing. The mitochondrial genome of S. asotus was identified as a 16,515 bp circular molecule containing 13 protein-coding genes (PCGs), 22 tRNA genes, and two rRNA genes, along with one A + T-rich control region. The AT content was 56.1%. Start codons ATG and GTG were found in 13 PCGs. Stop codons TAA, TAG, and AGA were observed in 13 PCGs. The heavy (H)-strand was predicted to have 12 PCGs and 14 tRNA and two rRNA genes, while the light (L)-strand was predicted to contain one PCGs and eight tRNA genes. The molecular phylogenetic analysis showed that S. asotus from Lake Biwa is genetically similar to S. asotus from China.

Aquatic freshwater fish like catfish, Silurus asotus , lives in microbe-rich environments, which enable this fish to develop necessary defense mechanisms. Antimicrobial peptides, along with other innate immune factors, are regarded as an important group in this defense. An antimicrobial peptide, which was isolated from the skin of S. asotus , was identified as a C-terminal fragment of 60S ribosomal protein L27 from S. asotus. The peptide was, then, designated Silurus asotus 60S ribosomal protein L27-derived antimicrobial peptide, Sa RpAMP. Primary structure analyses and cDNA cloning revealed that Sa RpAMP was 4185.36 Da and composed of 33 amino acids (AAs). Its precursor had a total of 136 AAs containing a pro-sequence of 103 AAs encoded by the nucleotide sequence of 512 bp that comprises a 5′ untranslated region (UTR) of 32 bp, an open reading frame (ORF) of 411 bp, and a 3′ UTR of 69 bp. Secondary structure analyses showed that Sa RpAMP had two α-helices with turns and coils and an amphiphilic structure, a finding consistent with the 3D model of the peptide. Sa RpAMP exhibited potent antibacterial activity comparable to piscidin 1, a powerful positive control. Its antimicrobial activity against fungus C. albicans was relatively weak. The antimicrobial activity of Sa RpAMP was not diminished by heat treatment and changes in pH but was abolished by proteolytic enzyme digestion. Membrane permeability assays suggested that Sa RpAMP interacts with both the outer and inner bacterial membranes. This was consistent with the results of lipid titration and quenching of Trp fluorescence that demonstrated Sa RpAMP's interaction with acidic liposomes. Collectively, these findings suggest that the identified peptide, Sa RpAMP, was the first antimicrobial peptide reported to be derived from the C-terminal region of 60S ribosomal protein L27. The findings also suggest that the action mechanism of Sa RpAMP involved the interaction of the peptide with the bacterial membranes. • An antimicrobial peptide (Sa RpAMP) identical to the C-terminus of 60S ribosomal protein L27 was identified from S. asotus. • Sa RpAMP was a cationic alpha-helical antimicrobial peptide with potent antimicrobial activity. • Sa RpAMP permeabilizes bacterial and artificial membranes. • Membrane interaction is involved in the action mechanism of Sa RpAMP. [ABSTRACT FROM AUTHOR]

We determined the complete mitochondrial DNA sequence of Silurus lithophilus, a catfish endemic to Lake Biwa, Japan. The mitogenome was 16,524 bp in length and the gene contents and order agreed with those of typical vertebrates. A molecular phylogenetic analysis based on 12 published Silurus mitogenomes showed that the mitogenome of S. lithophilus (LC520058) was closest to that of Silurus asotus from Japan (AP012022). These two mitogenomes were identical in the short (ca. 170 bp) gene region widely used in metabarcoding for environmental DNA analysis of fishes.

A single specimen of exotic Amur catfish, Silurus asotus Linnaeus, 1758, was captured by gillnet in the Tibet stretch of the Lancang River for the first time. (The Lancang River is an international river and in its lower course is also known as the Mekong River.) It is the first record of this fish species in eastern Tibet. The most possible pathway of the Amur catfish introduction into the Tibet stretch of the Lancang River was a human-mediated release known as life liberation activities or life release ceremony.

Amur catfish (Silurus asotus) is an ecologically and economically important fish species in Asia. Here, we assembled the female and male Amur catfish genomes, with genome sizes of 757.15 and 755.44 Mb, respectively, at the chromosome level using nanopore and Hi-C technologies. Consistent with the known diploid chromosome count, both genomes contained 29 chromosome-size scaffolds covering 98.80 and 98.73 % of the complete haplotypic assembly with scaffold N50 of 28.87 and 27.29 Mb, respectively. The female (n = 40) and male (n = 40) pools were re-sequenced. Comparative analysis of sequencing and re-sequencing data from both sexes confirmed the presence of an XX/XY sex determination system in Amur catfish and revealed Chr5 as the sex chromosome containing an approximately 400 kb Y-specific region (MSY). Gene annotation revealed a male-specific duplicate of amhr2 , namely amhr2y , in MSY, which is male-specific in different wild populations and expressed only in the testes. Amur catfish shared partially syntenic MSY and amhr2y genes with the southern catfish (S. meridionalis , Chr24), which were located on different chromosomes. High sequence divergence between amhr2y and amhr2 and high sequence similarity with amhr2y were observed in both species. These results indicate the common origin of the sex-determining (SD) gene and transition of amhr2y in the two Silurus species. Accumulation of repetitive elements in the MSY of both species may be the main driver of the transition of amhr2y. Overall, our study provides valuable catfish genomic resources. Moreover, determination of amhr2y as the candidate SD gene in Amur catfish provides another example of amhr2 as the SD gene in fish. [ABSTRACT FROM AUTHOR]

Silurus asotus is a widely distributed species, and mainly lives in the middle and lower layers of rivers, lakes, and reservoirs. In this study, we report the complete mitochondrial genome of S. asotus, which was 17,385 bp in length, containing 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, and a control region. Phylogenetic analyses indicated that S. asotus has a close relationship with S. soldatovi. This research work will provide some useful information on further molecular evolution studies of Siluridae species.

Copyright of Journal of Henan Agricultural Sciences is the property of Editorial Board of Journal of Henan Agricultural Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Clarias fuscus, Silurus asotus and Silurus meridionalis are economically important species in the aquaculture industry in China. However, comparative analysis of immune indices of C. fuscus, S. asotus, and S. meridionalis has been rarely been conducted. In the present study, head kidney and spleen indices and blood serum immunologically related enzyme activity of C. fuscus, S. asotus, and S. meridionalis were detected. Both head kidney and spleen body ratios were highest in S. meridionalis, followed by S. asotus, and lowest in C. fuscus. This suggests that the degree of lymphocyte proliferation and immune function of S. meridionalis might be strongest compared to S. asotus and C. fuscus. Blood serum lysozyme activity, superoxide dismutase (SOD) activity, and alkaline phosphatase activity, were highest in S. meridionalis, followed by S. asotus, but lowest in C. fuscus. Compared to S. asotus, acid phosphatase activity and catalase activity was higher in C. fuscus. Both acid phosphatase and catalase activities were highest in S. meridionalis, which was in line with lysozyme, superoxide dismutase (SOD), alkaline phosphatase, head kidney and spleen body ratios. This indicated that compared to S. asotus and C. fuscus, the immune function of S. meridionalis was strongest, and might have the greatest resistance to invaders like parasites, bacteria, and viruses. These results provide a theoretical basis for selection of varieties and optimization of germplasm in fish culture production and may be very valuable in future research. [ABSTRACT FROM AUTHOR]

The aims of this study were to determine the most suitable site and the histological responses to passive integrated transponder (PIT) tags inserted into three sites in far eastern catfish, Silurus asotus . During the experimental period, the tag retention rate and readability rate were greater for dorsal tags than for abdominal cavity or tail tags ( P < 0.05). The standard length, body weight, growth rate (GRW), condition factor (CF), and specific growth rate (SGR) were not significantly different among the experimental groups (all P > 0.05). GRW and SGR were lower in the winter than in the other season ( P < 0.05). In fish with abdominal tags, the tag was located in abdominal fat (in 60% of fish), around the kidney (15%), outside the air bladder (15%), or inside the air bladder (10%). Fibroblasts and a fibrous capsule were found in the tag site, but not in the epidermis. Melanopores and mucous cells were only found in the epidermis, and the area of mucous cells was larger than that of other cells in the epidermis. Based on the high rates of tag retention, readability, and survival, our results suggest that the dorsal muscle is the most favorable tag site for selective breeding systems of far eastern catfish. [ABSTRACT FROM AUTHOR]

A single specimen of exotic Amur catfish, Silurus asotus Linnaeus, 1758, was captured by gillnet in the Tibet stretch of the Lancang River for the first time. (The Lancang River is an international river and in its lower course is also known as the Mekong River.) It is the first record of this fish species in eastern Tibet. The most possible pathway of the Amur catfish introduction into the Tibet stretch of the Lancang River was a humanmediated release known as life liberation activities or life release ceremony. [ABSTRACT FROM AUTHOR]

A growth trial was conducted to determine the optimal incorporation level of dietary magnesium hydrogen phosphate (MHP, MgHPO4), which was manufactured from swine manure and phosphorus (P), required by juvenile far eastern catfish (Silurus asotus). Graded MHP of 0.5%, 1.0%, 1.5%, and 2.0%, and 2.0% monocalcium phosphate (MCP) each was added to the basal diet (control) in lieu of cellulose to become the range of available P (AP) from 0.4% to 0.8% of which diets were designated as control, MHP0.5, MHP1.0, MHP1.5, MHP2.0, and MCP, respectively. Control diet contained fish meal (20%), soybean meal (40%), wheat flour (27%), corn gluten meal (5%), fish oil (2%) and soy oil (2%) as main ingredients. Following a 24 h fasting, 540 fish with a mean body weight of 11.8 g were randomly allotted to 6 groups in triplicate, whereby 18 tanks (0.4×0.6×0.36 cm, water volume of 66 L) were prepared. The feeding experiment lasted for 8 weeks. Fish group fed the control diet showed the lowest weight gain (WG) and feed efficiency (FE) among treatments. The WG was, however, not significantly different (p>0.05) from that of fish group fed MHP0.5. Fish group fed MHP2.0 showed the highest WG and FE of which values were not significantly different from those of fish groups fed diets MHP1.0 and MHP1.5 as well as MCP (p>0.05) except fish groups fed control and MHP0.5. Aspartate aminotransferase was significantly decreased with an increase in available P, while alanine aminotransferase did not show a significant difference among treatment. The highest inorganic P in plasma was observed in fish fed MHP2.0. From the present results, a second-order regression analysis revealed that the optimal dietary MHP level and the AP requirement were found to be 1.62% and 0.7%, respectively. [ABSTRACT FROM AUTHOR]

Application effect of micropore aeration technique in rearing process of summer fingerlings of Silurus asotus from Poyang Lake was studied. This study provides an efficient safe aeration solution for large-scale fingerling rearing of Siiurus asotus. [ABSTRACT FROM AUTHOR]

The present study was conducted to investigate a supplemental effect of magnesium hydrogen phosphate (MHP, MgHPO4) as an alternative phosphorus (P) source on growth and feed utilization of juvenile far eastern catfish (Silurus asotus) in comparison with three conventional P additives (monocalcium phosphate (MCP), dicalcium phosphate (DCP) and tricalcium phosphate [TCP]) as positive controls. A basal diet as a negative control was prepared without P supplementation and four supplemental P sources were added at the level of 2%. Five groups of 450 fish having mean body weight of 11.3 g following 24 h fasting after three week adaptation period were randomly distributed into each of 15 tanks (30 fish/tank). Fish were hand-fed to apparent satiety twice a day for 8 weeks. Fish fed MHP had weight gain (WG), protein efficiency ratio and specific growth rate comparable to those fed MCP. Fish fed MHP and MCP had feed efficiency (FE) significantly higher (p<0.05) than those fed DCP. Fish groups fed control and TCP showed the lower FE than the other groups which was significantly different (p<0.05) from those of fish fed the other diets. Survival rate was not significantly different (p>0.05) among treatments. Fish fed control had the lowest hematocrit, which was significantly different (p<0.05) from that of fish fed MHP. Fish fed MCP and MHP had plasma P higher (p<0.05) than fish fed the other diets. Relative efficiencies of MCP, DCP and TCP to MHP were found to be 100.5 and 101.3%, 92.0 and 91.6%, and 79.1 and 80.9% for WG and FE, respectively. P availability was determined to be 88.1%, 75.2%, 8.7%, and 90.9% for MCP, DCP, TCP, and MHP, respectively. Consequently, MHP recovered from wastewater stream showed that as an alternative P source its performance was comparative with MCP on growth and feed utilization of juvenile far eastern catfish. [ABSTRACT FROM AUTHOR]

We investigated the post-passage movement patterns of three freshwater fish species, Carassius auratus, Hemibarbus longirostris, and Silurus asotus, frequently captured in a fishway trap as they were released into the lentic dam reservoir. Acoustic telemetry was used to monitor fish movement. Acoustic tags were attached to 10 individuals ( C. auratus, [ n = 6], Ca1-6; H. longirostris, [ n = 2], Hl1 and Hl2; and S. asotus, [ n = 2], Sa1 and Sa2). The individual (Sa1) was particularly monitored to changes of vertical distribution between day and night a depth transmitter. The lentic species, C. auratus and S. asotus, were grouped into those that moved into upper streams (Ca1, Ca2, Ca3, and Sa1) and those that stayed in the reservoir (Ca4, Ca5, Ca6, and Sa2); all individuals utilized almost the entire area of the reservoir. However, H. longirostris, which favor lotic environments, showed different responses; one (Hl1) immediately moved into one of upper the streams, whereas the other (Hl2) utilized the entire dam reservoir area. No significant correlations were observed between size of the C. auratus individuals (total length and total weight) and monitored parameters (total movement distance, movement distance per day, and number of receivers encountered). Moreover, S. asotus used the water at a mean depth of 2.89 ± 1.52 m, and its vertical distribution changed more actively during the night than that during the day. Therefore, the efficacy of the Jangheung Dam fishway could be improved through release of the confluence of the inflow streams at the dam reservoir, which would provide both lentic and lotic environments without extended migration for fish. [ABSTRACT FROM AUTHOR]

We determined the complete mitochondrial DNA sequence of Silurus lithophilus, a catfish endemic to Lake Biwa, Japan. The mitogenome was 16,524 bp in length and the gene contents and order agreed with those of typical vertebrates. A molecular phylogenetic analysis based on 12 published Silurus mitogenomes showed that the mitogenome of S. lithophilus (LC520058) was closest to that of Silurus asotus from Japan (AP012022). These two mitogenomes were identical in the short (ca. 170 bp) gene region widely used in metabarcoding for environmental DNA analysis of fishes. [ABSTRACT FROM AUTHOR]

The Amur catfish, Silurus asotus, is an economically important fish species in East Asia, but few genetic studies have been conducted on this species, especially those based on nuclear markers. Here, we isolated and characterized 47 novel polymorphic microsatellite loci in the genome of S. asotus using 454 sequencing. We screened 70 primers and 48 of them generated amplification products. Forty-seven of the amplification products were polymorphic in a population of 40 collected from the upper Yangtze River. The number of alleles varied from 3 to 15, and the observed and expected heterozygosities varied from 0.300 to 0.800 and 0.305 to 0.866, respectively. The average polymorphic information content (PIC) of all loci was 0.682, indicating high levels of polymorphism. In addition, cross-species amplification in a congener species, Silurus meridionalis showed a high level of transferability (79.2 %), which confirmed that the microsatellite markers developed here could be used effectively for other related catfish species. [ABSTRACT FROM AUTHOR]

This study determined the haematological changes in Korean catfish, Silurus asotus, experimentally infected with Edwardsiella tarda. Twenty-four or 48 h after infection with 1 × 104 colony-forming units (CFU) mL−1 of E. tarda, the fish were anaesthetized and the blood was collected. The haematological and biochemical tests included haematocrit (Ht), haemoglobin (Hb), leucocyte counts (Lc), total calcium (Ca), total protein (TP) concentration, alkaline phosphatase (ALP), glucose (GLU), aspartate aminotransferase, lysozyme and differential leucocyte populations. After 24- and 48-h infection, the values of Ht, Hb, Lc, TP, ALP and GLU were significantly decreased with respect to the control. Aspartate aminotransferase and lysozyme activity in both the 24- and 48-h groups exhibited higher levels compared with those in the control. However, the bacterial infection did not induce any significant alteration in the Ca concentration. After the 48-h infection, neutrophils and macrophage populations were reduced whereas lymphocytes were increased with respect to those in the control and the 24-h infection groups. The present study demonstrates that E. tarda infection causes haemato-biochemical responses that are related to the general physiological condition and defence system in catfish. [ABSTRACT FROM AUTHOR]

Mass mortality of Korean catfish, Silurus asotus, occurred in a culture farm situated in Jeollabukdo Province, Korea. The cumulative mortality rates reached up to 5% of the total fish in the farm per day. In clinical signs, the affected fish showed abdominal distension, vent protrusion, enteritis, liver congestion and abscess-like lesions in enlarged spleen and kidney. Histopathologically, in the liver, hepatocytes lost fat and underwent atrophy or necrosis. The spleen showed necrotized splenocytes and a haemorrhagic pulp. In the kidney, glomerular destruction, degeneration of renal tubular epithelial cell and haemorrhage were observed. However, necrotic muscular lesions were not observed. A pure bacterial isolate was obtained from the liver, spleen and kidney lesions of affected fish. Experimental infection of normal catfish with the isolate resulted in the development of clinical signs similar to those seen on the farm. The isolates were identified as Edwardsiella tarda through biochemical tests (99.4%) and analysis of bacterial genes (16S rDNA) sequences (98%). The bacteria possessed two virulent genes: sodB and katB genes. These results suggest that E. tarda can act as a pathogen of farmed catfish. This is the first report showing that E. tarda caused mortality in cultured Korean catfish. [ABSTRACT FROM AUTHOR]

Silurus asotus is a widely distributed species, and mainly lives in the middle and lower layers of rivers, lakes, and reservoirs. In this study, we report the complete mitochondrial genome of S. asotus, which was 17,385 bp in length, containing 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, and a control region. Phylogenetic analyses indicated that S. asotus has a close relationship with S. soldatovi. This research work will provide some useful information on further molecular evolution studies of Siluridae species. [ABSTRACT FROM AUTHOR]

Prey fish selection by Far Eastern catfish and largemouth bass were examined using bluegill, Japanese dace and crucian carp as food fish. In both aquaria (1.2 m × 0.45 m) and ponds (2.8 m × 1.2 m), bluegill was not preyed on by catfish and bass more than dace and crucian carp. In aquaria, there was no significant difference in the consumption of dace and crucian carp between catfish and bass, but in ponds, catfish preyed on dace and crucian carp more and less than bass, respectively. In the case that only bluegill and catfish were introduced in ponds, catfish consumed 4–15 g of bluegill per day. The introduction of catfish into ponds and lakes for the purpose of eradicating bluegill is considered appropriate for areas with few native fish species. [ABSTRACT FROM AUTHOR]

The annual reproductive cycle, including the first maturity of ovarian development and plasma levels of testosterone (T) and estradiol-17β (E2), was examined in female Japanese catfish Silurus asotus reared under natural conditions. In addition, the possible period that final oocyte maturation and ovulation can be induced by human chorionic gonadotropin (hCG) injection were investigated. Results showed that female Japanese catfish matured 1 year after hatching under reared conditions. The beginning of vitellogenesis was in March and ovarian development and plasma T and E2 levels peaked in June. Thereafter, the gonadosomatic index gradually decreased to October and regression of oocytes at the tertiary yolk globule stage was observed. Female Japanese catfish could be induced to final oocyte maturation and ovulation by hCG treatment during the period from June to September. In addition, the fertilization rates were relatively high and stable during this period. These results suggest that yearling female Japanese catfish can be used as brood stock for seed production. This is the first study to investigate the annual reproductive cycle in Japanese catfish. These data will provide useful information regarding brood stock management and seed production. [ABSTRACT FROM AUTHOR]

The mating behavior of the rock catfish Silurus lithophilus (Siluriformes: Siluridae), a species endemic to the Lake Biwa system, was observed from May to July in 1989–1994 along the rocky shore of the lake's outlet, the Seta River. The mating behavior of S. lithophilus involved a certain behavioral sequence: “chasing,”“clinging,” and “enfolding” while “squeezing” by the male; and “circling” by the spawned pair. The mating behavior of this species was basically similar to that of S. biwaensis, but greatly different from that of S. asotus, which spawns in running water (in ditches). The mating behavior of S. lithophilus (and S. biwaensis) might have developed as an adaptation to lentic environments such as the shores of the large river or the lake. [ABSTRACT FROM AUTHOR]

The east Asian catfish Silurus asotus is a common species living in fresh water in Japan. The complete mitochondrial genome of the S. asotus from Lake Biwa in Japan was analyzed using next-generation sequencing. The mitochondrial genome of S. asotus was identified as a 16,515 bp circular molecule containing 13 protein-coding genes (PCGs), 22 tRNA genes, and two rRNA genes, along with one A + T-rich control region. The AT content was 56.1%. Start codons ATG and GTG were found in 13 PCGs. Stop codons TAA, TAG, and AGA were observed in 13 PCGs. The heavy (H)-strand was predicted to have 12 PCGs and 14 tRNA and two rRNA genes, while the light (L)-strand was predicted to contain one PCGs and eight tRNA genes. The molecular phylogenetic analysis showed that S. asotus from Lake Biwa is genetically similar to S. asotus from China., Competing Interests: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article., (© 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.)