Scatter-spawning of the catfish,Silurus asotus

Reproductive behaviour of the catfish,Silurus asotus was studied in temporary waters around paddy fields. Spawning occurred nocturnally during the first week from the initiation of irrigation. In reproductive activities, a male first energetically pursued a female with its head near to the female’s belly (chasing) and then began to cling to the female’s body from the side, bending its tail or head (clinging). Finally the male enfolded the female’s body, with its anus near to the female’s (enfolding). In some cases, 2–4 males pursued a single female and two males enfolded a female at the same time. Although no aggressive behaviour was evident between males, it was always the largest male that could most frequently approach and enfold the female. The mating pair moved a long distance in a ditch, paddy field and/or creek, performing reproductive activities. It is thought that the spawning site and period of spawning of the fish enable the larvae to avoid the danger of predation and to efficiently feed, firstly on plankton and later on larvae of other fishes which become abundant during the irrigation period. Although some eggs and larvae may die due to the drying out or high water temperatures of such unstable temporary waters, scattering eggs may reduce the incidence of the annihilation of the young.     

A unique epidermal mucus lectin identified from catfish (Silurus asotus): first evidence of intelectin in fish skin slime

The present study reports a new type of skin mucus lectin found in catfish Silurus asotus. The lectin exhibited calcium-dependent mannose-binding activity. When mannose eluate from chromatography with mannose-conjugated agarose was analysed by SDS-PAGE, the lectin appeared as a single 35-kDa band. Gel filtration showed that the lectin forms monomers and dimers. A 1216-bp cDNA sequence obtained by RACE-PCR from the skin encoded a 308 amino acid secretory protein with homology to mammalian and fish intelectins. RT-PCR demonstrated that the lectin gene was expressed in the gill, kidney and skin. Subsequent sequencing revealed the presence of an isoform in the gills. Antiserum detected the intelectin protein in club cells in the skin and gill, renal tubules and blood plasma. Although intelectin gene expression was not induced by in vivo bacterial stimulation, the intelectin showed agglutination activity against the pathogenic bacterium Aeromonas salmonicida, suggesting that the lectin plays an important role in self-defence against bacteria in the skin surface of the catfish. These findings represent one of the few examples of characterization and functional analysis of a fish intelectin protein.     

Structural characterization of a rhamnose-binding glycoprotein (lectin) from Spanish mackerel (Scomberomorous niphonius) eggs

A rhamnose-binding glycoprotein (lectin), named SML, was isolated from the eggs of Spanish mackerel (Scomberomorous niphonius) by affinity and ion-exchange chromatographies. SML was composed of a non-covalently linked homodimer. The SML subunit was composed of 201 amino acid residues with two tandemly repeated domains, and contained 8 half-Cys residues in each domain, which is highly homologous to the N-terminal lectin domain of calcium-independent alpha-latrotoxin receptor in mammalian brains. Each domain has the same disulfide bonding pattern; Cys10-Cys40, Cys20-Cys99, Cys54-Cys86 and Cys67-Cys73 were located in the N-terminal domain, and Cys108-Cys138, Cys117-Cys195, Cys152-Cys182 and Cys163-Cys169 were in the C-terminal domain. SML was N-glycosylated at Asn168 in the C-terminal domain. The structure of the sugar chain was determined to be NeuAc-Galbeta1-4GlcNAcbeta1-2Manalpha1-6-(NeuAc-Galbeta1-4GlcNAcbeta1-2Manalpha1-3)Manbeta1-4GlcNAcbeta1-4GlcNAc-Asn.     

Structural characterization of a rhamnose-binding glycoprotein (lectin) from Spanish mackerel (Scomberomorous niphonius) eggs

A rhamnose-binding glycoprotein (lectin), named SML, was isolated from the eggs of Spanish mackerel (Scomberomorous niphonius) by affinity and ion-exchange chromatographies. SML was composed of a non-covalently linked homodimer. The SML subunit was composed of 201 amino acid residues with two tandemly repeated domains, and contained 8 half-Cys residues in each domain, which is highly homologous to the N-terminal lectin domain of calcium-independent α-latrotoxin receptor in mammalian brains. Each domain has the same disulfide bonding pattern; Cys10–Cys40, Cys20–Cys99, Cys54–Cys86 and Cys67–Cys73 were located in the N-terminal domain, and Cys108–Cys138, Cys117–Cys195, Cys152–Cys182 and Cys163–Cys169 were in the C-terminal domain. SML was N-glycosylated at Asn168 in the C-terminal domain. The structure of the sugar chain was determined to be NeuAc-Galβ1-4GlcNAcβ1-2Manα1-6-(NeuAc-Galβ1-4GlcNAcβ1-2Manα1-3)Manβ1-4GlcNAcβ1-4GlcNAc-Asn.     

Effect of meal size on postprandial metabolic response in Chinese catfish (Silurus asotus Linnaeus)

The effect of relative meal size (0.5–24% body mass) on specific dynamic action (SDA) was assessed in Chinese catfish (Silurus asotus Linnaeus) (30.90±1.30 g) at 25.0°C; the cutlets of freshly killed loach without viscera, head and tail were used as a test meal. There was no significant difference in either SDA duration or peak oxygen consumption (VO₂) among low meal size ranges. But both increased linearly as meal size increased from 2 to 24% without reaching a plateau. Factorial metabolic scope was 5.92 in fish fed with 24% body mass, the highest documented feeding metabolic scope value in fish till now. The Peak VO₂ of satiated meal size groups (175.85±10.55 mg O₂ h⁻¹) was above 80% of maximum metabolic rate during locomotion recovery process (215.48±7.07 mg O₂ h⁻¹). The relationship between energy expended on SDA (E) and energy ingested (I) was described as: E=0.0000432I ²+0.140I+2.12. The lowest value of SDA coefficient appeared at 2% body mass group.     

Isolation and identification of the major plasma fibronectin cDNA from Japanese catfish Silurus asotus

Major plasma fibronectin from Japanese catfish was isolated using affinity chromatography, and the fibronectin was digested with thermolysin. Peptide sequences of the fragments were obtained by peptide sequencer. Complete fibronectin cDNA was obtained from Japanese catfish liver cells using 5'-rapid amplification of cDNA end (RACE) and 3'-RACE based on the peptide sequences. It consists of a 6885 bp open reading frame, which is putatively translated to a protein of 2295 amino acids resides. The catfish fibronectin has 12 type-I modules, 2 type-II modules and 15 type-III modules, and variable sites V and lacks both EIIIA and EIIIB sites. Homology of the entire amino acids residues of catfish fibronectin with those of mammals (Homo sapiens, Rattus norvegicus, Bos taurus) is only 47-48% and 57% with that of Danio rerio. However, amino acid sequence of type-I module 3 and type-I module12 are highly conserved and homology exceeds 80% with corresponding regions of the mammals, Xenopus laevis and fish species (Silurus asotus and D. rerio). Phylogenetic analysis indicates that only type-I module 4 shows a different pattern of phylogenetic tree. One major fibronectin mRNA was detected in whole liver and hepatocytes by northern hybridization, however, five to six other bands were also detected in both samples.     

A novel rhamnose-binding lectin family from eggs of steelhead trout (Oncorhynchus mykiss) with different structures and tissue distribution

An L-rhamnose-binding isolectin named STL3 (subunit Mr, 21.5 k) was isolated from eggs of the steelhead trout (Oncorhynchus mykiss) in addition to STL1 (subunit Mr, 31.4 k) and STL2 (subunit Mr, 21.3 k) that had been already isolated. STLs were composed of noncovalently linked subunits. The primary structures of STL1 and STL3 were analyzed by the combined use of protein sequencing and cDNA sequencing. A cDNA encoding STL2, of which the protein sequence had been previously studied, was also analyzed. The STL1 subunit (289 amino acid residues) had different structural properties compared to those of the STL2 subunit (195 amino acid residues) and the STL3 subunit (195 amino acid residues); e.g., the number of repeated domain (three for STL1, and two for STL2 and STL3), although all of them were composed of tandemly repeated homologous domains (40 to 53% identities). The lectin levels in various tissues and during the embryonic development showed that STL1 had different distribution and expression profiles from those of STL2 and STL3. Although STL1 could be detected in several tissues and serum of both male and female steelhead trout, STL2 and STL3 were only abundant in the ovary. STL2 and STL3 levels dramatically decreased just after hatching, however, the STL1 level increased temporarily. These results indicate that the multiple lectins from eggs of the steelhead trout form a novel rhamnose-binding lectin family with different structures and tissue distribution to share distinct functions in eggs.     

Mitochondrial genome of Silurus asotus (Teleostei: Siluriformes)

The complete mitogenome sequence of the Amur catfish Silurus asotus was determined using long PCRs. The genome was 16,528 bp in length and contained 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, and 1 control region; the gene composition and order of which was similar to most other vertebrates. The overall base composition of the heavy strand is 30.5% A, 25.8% T, 28.0% C, and 15.8% G, with an AT content of 56.3%. The mtDNA sequence of S. asotus shared 93.6% and 90.6% sequence identity with that of Silurus meridionalis and Silurus glanis. This mitogenome sequence data would play an important role in silurid catfish phylogenetics and siluriform catfish systematics in general.     

Genetic structure and phylogeography of European catfish (Silurus glanis) populations

The genetic structure of Silurus glanis (Europe's largest freshwater fish species) across most of its natural distribution was investigated using 10 microsatellite loci. The revealed levels of genetic diversity were much higher than previous allozyme and restriction fragment length polymorphism mitochondrial DNA analyses had shown; relative levels of variability among populations were however, in good agreement with the previous studies. Populations from large basins (Volga and Danube rivers) were the most polymorphic, while samples from the smaller Greek rivers, which are more prone to genetic bottleneck, exhibited the lowest levels of genetic diversity. Microsatellite multilocus genotyping permitted the assignment of individual fish to their population of origin with a score as high as 98.3%. Despite the great genetic differentiation of S. glanis populations, no consistent pattern of geographical structuring was revealed, in contrast to previous studies of European freshwater fish species. A model of isolation by distance seems more probable and a hypothesis of recent dispersion from only one glacial refugium is proposed. The discovery of the highest levels of microsatellite and mitochondrial diversity in the Volga sample and the presence of river connections, during the Pleistocene, between this area and all major areas of the present catfish distribution, place this refugium around the Ponto-Caspian region. Combining these data with those from previous studies, a number of markers are now available to monitor wild and hatchery populations even at the individual level.     

Difference in response by two cyprinid species to predatory threat from the nocturnal catfish Silurus asotus

Response to predators may not be identical between different prey species with different life histories and body sizes, particularly when the threat of predation is not great. To clarify this hypothesis, we introduced two prey species (10 Japanese dace, Tribolodon hakonensis, and 10 pale chub, Zacco platypus) into each experimental pond (in total, 8 ponds×4 trials) in which benthic algae had been allowed to grow. The presence or absence of Far Eastern catfish, Silurus asotus, and a refuge for prey fish was used to produce four treatments. The presence of catfish and/or a refuge did not affect either the feeding behavior or growth rate of Japanese dace. In contrast, when catfish were present and no refuge was available, the incidence of bottom feeding for pale chub greatly decreased. Pale chub growth rate was low when catfish were present and a refuge was available, indicating that pale chub spent more of their time in the refuge and lost opportunities of acquiring food. Japanese dace can reach a threshold size at which the prey are safe from predation, but pale chub cannot, and this may explain the differences in response to predators of the two species.     

南方鲇

南方鲇是我国特有的大型肉食性名优鱼类。具有个体大,生长快,抗病力强等特点。其形态特征、生活习性、繁殖与生长、人工养殖等都具有自身的特殊性,也是一种很好的实验研究材料。     

Stereotyped sequence of mating behavior in the Far Eastern catfish, Silurus asotus, from Lake Biwa

 Mating behavior of the Far Eastern catfish, Silurus asotus (Siluriformes: Siluridae), was observed in a ricefield system facing the shore of Lake Biwa in mid-May to early June in 1990–1997. A set behavioral sequence similar to those of two other silurid fishes, S. biwaensis and S. lithophilus, both endemic to the Lake Biwa system, was observed: “chasing,”“clinging,”“enfolding” while “squeezing” by the male, and “circling” by the spawning pair. This form of mating behavior is quite different from that of S. asotus reported from the Ooi River system in Kyoto Prefecture, which mainly spawns in running water in ditches. Received: April 10, 2001 / Revised: November 5, 2001 / Accetped: November 20, 2001     

Spawning and season affect lipid content and fatty acid composition of ovary and liver in Japanese catfish (Silurus asotus)

The influences of spawning and season on lipid content, lipid classes, and fatty acid composition were assessed in ovary and liver of wild and cultured Japanese catfish (Silurus asotus). The lipid content (7.3+/-1.6 g/100 g wet wt.) of ovary from wild catfish at spawning was higher than that at post-spawn. However, no influence of spawning on the lipid content of liver was observed. Docosahexaenoic acid [DHA, C22:6(n-3)] in ovary lipids was 12.3+/-0.5% of total fatty acids. The percentage of n-7 monounsaturated fatty acids in triacylglycerol from the ovary and liver in the spawning season was high. Percentages of C22:6(n-3) in phosphatidylcholine and phosphatidylethanolamine from ovary were higher during spawning than after spawning. No significant differences were observed in the lipid content of ovary and liver from cultured catfish between seasons (summer vs. winter). Content of arachidonic acid (C20:4n-6) in ovary and liver from cultured catfish was higher in summer than in winter. There were differences in lipid classes of ovary and liver by spawning and season. These results suggest that the lipid metabolism in Japanese catfish is greatly influenced by spawning and season.     

Thresholds of retinal and extraretinal photoreceptors measured by photobehavioral response in catfish,Silurus asotus

Summary Light thresholds of retinal and extraretinal photoreceptors in catfish were examined by the photobehavioral response using a method in which reflex body movements are recorded. Thresholds were determined in six groups, (A) intact, (B) ophthalmectomized, (C) pinealectomized, (D) ophthalmectomized + pinealectomized, (E) ophthalmectomized, pinealectomized and skinless over the brain (skinless fish) and (F) ophthalmectomized, pinealectomized and dorsally covered with aluminum foil over the brain (covered fish). All these fishes displayed short term activity to white light stimulation after being dark adapted for more than 5 h. The lowest threshold was obtained in the intact group (2.0×10^–4 W/cm²). The thresholds of lateral eyes and the pineal organ were 3.4×10^–3 and 1.5×10^–2 W/cm², respectively. Without lateral eyes and pineal organ, catfish still responded to light, indicating the possible existence of extraretinal nonpineal photoreceptors (ENPs). The threshold of ENPs was 3.3 W/cm². The localization of ENPs was assumed to be in the brain from the experiment with the combination of skinless and covered fish.Abbreviation ENP extraretinal nonpineal photoreceptor     

Resistance of the European catfish (Silurus glanis) to channel catfish virus

European catfish (Silurus glanis) fingerlings (2 to 4 g each) were tested for susceptibility to channel catfish virus (CCV). They had supported CCV replication at 2 days after intraperitoneal injection with 0.1 ml of saline containing 10⁵ TCID₅₀. Homogenized visceral organs (liver, kidney and spleen) contained 10⁴ TCID₅₀/0.1 ml at 2 days post inoculation (PI) but at 4 days the titer decreased to 10¹ TCID₅₀. Bathing European catfish in CCV yielded only one positive sample with à titer of 10^0.83 TCID₅₀ per 0.1 ml of tissue. No clinical signs of CCV developed and no virus related deaths occurred.     

Tandem repeat L-rhamnose-binding lectin from the skin mucus of ponyfish, Leiognathus nuchalis

Two lactose-binding lectins (PFL-1 and -2) were identified in the skin mucus of ponyfish, Leiognathus nuchalis. The molecular masses of PFL-1 and -2 were estimated to be 24 and 30kDa, respectively. Cloning of the PFL-1 cDNA demonstrated its unique tandem repeat structure composed of two homologous domains with 41.7% internal identity. Furthermore, PFL-1 exhibited homology with L-rhamnose-binding lectins previously purified from the eggs of fish and sea urchins. The N-terminal amino acid sequence of PFL-2 was similar to that of PFL-1, suggesting that this protein is an isotype of PFL-1. The PFL-1 gene was expressed in the skin, an important line of defense against pathogens in fish, but was not expressed in any of the other tissues tested here. PFL-1 is the fourth type of fish skin mucus lectin to be identified, suggesting that different species of fish express different types of lectin in their skin mucus.     

Electron microscopic demonstration of lectin binding sites in the taste buds of the European catfish Silurus glanis (Teleostei)

Summary Taste buds in the European catfish Silurus glanis were examined with electron microscopic lectin histochemistry. For detection of carbohydrate residues in sensory cells and adjacent epithelial cells, gold-, ferritin-and biotin-labeled lectins were used. A post-embedding procedure carried out on tissue sections embedded in LR-White was applied to differentiate between the sensory cells: The lectins from Helix pomatia (HPA) and Triticum vulgare (WGA) bound to N- acetyl-galactosamine and to N-acetylglucosamine residues occurring especially in vesicles of dark sensory cells. This indicates a secretory function of these cells. Most light sensory cells — with some exceptions, probably immature cells —, are HPA-negative. The mucus of the receptor field and at the top of the adjacent epithelial cells was strongly HPA-positive. Pre-embedding studies were performed in order to obtain information about the reaction of the mucus with lectins under supravital conditions. The mucus of the taste bud receptor field exhibited intensive binding to WGA, but not to the other lectins tested. Most lectins bound predominantly to the surface mucus of the nonsensory epithelium and to the marginal cells close to the receptor field. The strong lectin binding to mucins and the relatively weak lectin binding to cell surface membranes in pre-embedding studies suggest that the mucus possibly serves as a barrier which is passed selectively only by a small amount of lectins or lectincarbohydrate complexes. Lectin-carbohydrate interactions may play a role in recognition phenomena on the plasmalemmata of the taste bud sensory cells. Recognition processes directed to bacteria or viruses should be considered as well.Parts of this investigation were presented at the XI. Annual Meeting of the Association for Chemoreception Sciences (AChemS XI), held at Sarasota, Fl, April 12–14, 1989 (Witt and Reutter 1989)