Definition of the USDA103 strain of channel catfish (Ictalurus punctatus)

Although there are differences in performance between genetic groups of channel catfish, identification and management of these groups is difficult because catfish strains look alike and individuals cannot be tagged efficiently. Thus, US catfish producers have not been able to objectively identify fish from different strains or populations, and it has been difficult for them to maintain the genetic purity of populations on the farm. We have developed a multiplexed microsatellite genotyping system to define catfish populations based on allelic frequency and exclusion. A commercial catfish genotype database was developed using catfish samples collected from 24 processing plants in the four main US catfish-producing states. The utility of the system was tested by the molecular characterization of the USDA103 research strain. Using eight microsatellite loci, the probability of falsely classifying an individual non-USDA103 catfish as a USDA103 was 0.0065. From a sample of 50 fish from a putative USDA103 pond, the probability of falsely including two non-USDA103 fish was 1 x 10(-105), and the conservative probability of falsely excluding two USDA103 fish was 1 x 10(-6). This genotyping system provides channel catfish producers with an objective mechanism for identification and management of genetically selected fish.     

Molecular characterization of the insulin-like growth factor-I (IGF-I) gene in channel catfish (Ictalurus punctatus)

The insulin-like growth factor I (IGF-I) gene was characterized in channel catfish. Partial cDNA sequence, missing exon 1 and part of exon 2, was obtained in 5'- and 3'-RACE experiments. Direct sequencing of two bacterial artificial chromosome clones revealed gene structure and provided sequence from 640 bp upstream of the initiator methionine to 136 bp beyond the polyadenylation site. Genomic sequence contained a putative TATA box 506 bp upstream of the initiator methionine. The 477-bp reading frame within five exons encoded a 159-amino acid (aa) pre-propeptide highly similar to IGF-I in higher vertebrates. The sequence encoding the signal peptide was unique in catfish and contained 70% G+C content with the potential for a stable stem-loop structure. Full-length cDNA was only maintained in recombination-deficient (DH10B) strain E. coli. Levels of IGF-I mRNA were highest in liver, followed by brain and muscle, then heart and kidney (P<0.05). A CT/GA dinucleotide microsatellite in intron 1 was highly polymorphic in commercial channel catfish, and permitted placement of the IGF-I gene on the catfish genetic map. However, specific IGF-I alleles were not correlated with differences in growth rate from 100 to 130 days post-hatch in USDA103 line catfish.     

Gastrointestinal torsion in a channel catfish (Ictalurus punctatus)

A case of gastrointestinal torsion with dilatation in a farm-raised channel catfish (Ictalurus punctatus) was examined at the Thad Cochran National Warmwater Aquaculture Center (Stoneville, Mississippi, USA). The affected fish was a gravid female broodfish, which displayed pale gills and a markedly distended abdomen. Internal examination revealed that the gastrointestinal tract and ovaries were rotated around each other four times in a counterclockwise direction as viewed in right lateral recumbency. The catfish had a markedly distended gastrointestinal tract, pale liver, hypoplastic spleen, hypoplastic swim bladder, and high volume of ascitic fluid. Blood analysis indicated multiple abnormalities, including severe anemia and metabolic acidosis. The etiology of the torsion was uncertain; however, the presence of a hypoplastic swim bladder most likely allowed for increased movement of the gastrointestinal tract and ovaries. When examining cases of abdominal distention in fish, gastrointestinal torsion can be considered among the differential diagnoses.     

Cortisol-induced hematologic and immunologic changes in channel catfish (Ictalurus punctatus)

1. Intravenous injections of physiologic doses of cortisol resulted in both hematologic and immunologic changes in channel catfish peripheral blood leucocytes. These changes mimicked those seen when catfish were acutely stressed by handling and transport. 2. Eighteen hours after the administration of cortisol, decreases in the number of circulating lymphocytes and concomitant increases in the number of circulating neutrophils were observed, i.e. to the same levels seen previously in stressed fish. 3. Functional analysis of peripheral blood leucocytes from cortisol-injected fish indicated that the remaining lymphocytes were no longer capable of responding to mitogenic stimuli. 4. This suppression of mitogenic stimuli was not seen when peripheral blood leucocytes were cultured in vitro with physiologic doses of cortisol. 5. This latter observation suggests that the cortisol alone was probably not directly responsible for the loss of responsiveness but possibly acted in vivo as an initiator of other events that eventually resulted in the observed immunosuppression.     

Histology of cultured channel catfish, Ictalurus punctatus (Rafinesque)

Dissolved oxygen and un-ionized ammonia concentrations were monitored in 12 0.04 ha earthen ponds stocked with 10 000 channel catfish, Ictalurus punctatus ,/ha. Gill, liver and trunk kidney tissue samples were removed periodically for histological examination. Total ammonia and dissolved oxygen levels were in the ranges reported for catfish culture at this level of intensity. Average un-ionized ammonia nitrogen concentrations ranged from 20 to 67 μgh⁻¹ and average daily maxima ranged from 63 to 183 μgh⁻¹. Gill lesions characteristic of un-ionized ammonia exposure were common in fish from all ponds.     

Ultrastructure of the liver in channel catfish Ictalurus punctatus (Rafinesque)

Livers of 38 channel catfish were studied by light and electron microscopy and the morphology of hepatocytes, endothelial cells, Kupffer cells, fat-storing cells, macrophages, exocrine pancreatic cells, and epithelium of bile pre-ductules and ducts was described, Hepatocytes contained large peri-canalicular bodies which showed acid hydrolase activity. A comparison between catfish liver and that of other teleosts was made. The applicability of the findings to pathobiological studies of teleost liver is described.     

Immune hypersensitivity in the channel catfish, Ictalurus punctatus (Rafinesque)

Channel catfish, Ictalurus punctatus , exhibited passive cutaneous anaphylaxis (PCA) when sensitized with Flexibacter columnaris antiserum produced in channel catfish (the first record of PCA in any fish), but not when sensitized with homologous antiserum against channel catfish virus. Channel catfish did not give delayed skin hypersensitivity responses after immunization with either channel catfish virus or F. columnaris .     

Comparative study of mannose-binding C-type lectin isolated from channel catfish (Ictalurus punctatus) and blue catfish (Ictalurus furcatus)

Mannose-binding C-type lectin (MBL) was isolated from channel catfish (Ictalurus punctatus) NWAC 102 and 103 strains, blue catfish (Ictalurus furcatus) D+B and Rio Grande strains, hybrid catfish (channel catfish female NWAC 103 x blue catfish male D+B) sera, and purified by affinity chromatography from channel catfish Norris strain serum. Reduction of purified channel catfish MBL with 2-ME yielded a single band of 62 kDa by SDS-PAGE and Western blot analysis using guinea pig anti-MBL IgG as primary antibody. Channel catfish NWAC 102 strain, channel catfish NWAC 103 strain and hybrid catfish sera had molecular masses of 63 kDa for MBL. Blue catfish (D+B strain) serum MBL had a molecular mass of 66 kDa. Rio Grande blue catfish serum MBL had a molecular mass of 65 kDa. Amino acid composition analysis (mol%) of the affinity-purified channel catfish MBL found a high content of serine present. Functional binding studies of channel catfish and blue catfish MBLs binding to Edwardsiella ictaluri were done using a dot-immunoblot ELISA method. A dot-immunoblot ELISA binding assay was done to compare nine different strains and species of channel catfish and blue catfish for their levels of serum MBL. Blue catfish had higher levels of MBL than did the various strains of channel catfish tested. MBL could be used as a genetic marker for selection of disease resistance in the different strains of catfish used in aquaculture. This study describes the presence of serum MBL in catfish and evidence for a C-type lectin complement pathway of innate immunity.     

Structure and expression of transferrin gene of channel catfish,Ictalurus punctatus

Transferrin is important in iron metabolism and has been reported to be involved in disease defence responses after bacterial infection. In this study, we identified, sequenced, and characterized the transferrin gene from channel catfish, Ictalurus punctatus. The catfish transferrin gene was similar to those of other vertebrate species with 17 exons and 16 introns. Sequence analysis indicated the presence of the two duplicated lobes, each containing two sub-domains separated by a cleft harboring the iron-binding site, suggesting their structural conservation. The channel catfish transferrin cDNA encodes 679 amino acids with 42–56% similarity to known transferrin genes from various species. Southern blot analysis suggested the presence of two copies of the transferrin gene in the catfish genome, perhaps arranged in a tandem fashion. The catfish transferrin gene was mapped to a catfish BAC-based physical map. The catfish transferrin gene was highly expressed in the liver, but expression was low in most other tested tissues. Transferrin expression was significantly up-regulated after infection with Edwardsiella ictaluri, the causative agent of enteric septicemia of catfish. Such induction was also found with co-injection of iron-dextran and E. ictaluri, while transferrin expression was not significantly induced with the injection of iron-dextran alone.     

Cloning and characterisation of a channel catfish (Ictalurus punctatus) Mx gene

A 2.5 kb full-length cDNA clone of a channel catfish (Ictalurus punctatus) Mx gene was obtained using RACE (rapid amplification of cDNA ends) polymerase chain reaction (PCR) from RNA extracted from the liver of poly I:C stimulated channel catfish. The gene consists of an open reading frame of 1905 nucleotides encoding a 635 amino acid protein. The predicted protein is 72.5 kDa and contains the dynamin family signature, a tripartite GTP binding motif and a leucine zipper, characteristic of all known Mx proteins. The catfish Mx protein exhibited 79% identity with perch Mx and between 71% and 74% identity with the three Atlantic salmon and the three rainbow trout Mx proteins. Mx mRNA was constitutively expressed in channel catfish ovary (CCO) cells, but in higher quantities in response to poly I:C treatment. Mx was induced in channel catfish following injection with channel catfish virus (CCV) and poly I:C.     

不同水温下氟甲砜霉素在斑点叉尾鮰体内的药代动力学研究

研究不同水温(18℃和28℃)条件下,单剂量(10mg/kgb·w)强饲氟甲砜霉素,在斑点叉尾鮰(Ictaluruspunc-tatus)体内药代动力学特征.采用高效液相色谱紫外检测法可以同时检测血浆中氟甲砜霉素及其代谢物氟甲砜霉素的浓度.用3p97药代动力学软件处理药时数据.结果表明:在不同水温条件下氟甲砜霉素在斑点叉尾鮰体内的药时数据均符合一室开放式模型.药时规律符合理论方程C血浆=71921(e-0.036t-e-0.18t)和C血浆=91061(e-0.081t-e-0.301t).18℃和28℃的条件下,主要药代动力学参数:吸收半衰期T1/2ka分别为31845h和21301h,消除半衰期T1/2ke分别为191118h和81519h,达峰时间Tpeak分别为111136h和51953h,最大血药浓度Cmax分别为41074μg/mL和41226μg/mL,曲线下面积AUC分别为1741547(μg/mL)/h和811279(μg/mL)/h,平均驻留时间MRT分别为271581h和121290h,相对表观分布容积V/F(c)分别为11580L/kg和115121L/kg.采用氟甲砜霉素防治斑点叉尾鮰细菌性疾病,建议在18℃左右口服10mg/kg体重剂量的氟甲砜霉素,2d给药1次;在28℃左右口服10mg/kg体重剂量的氟甲砜霉素,1d给药1次.试验过程中在斑点叉尾鮰血浆样品中未检测到氟甲砜霉素的主要代谢物氟甲砜霉素胺.       

Genetic and virulence characterization of Flavobacterium columnare from channel catfish (Ictalurus punctatus)

Aim: To develop a method for conducting pulsed-field gel electrophoresis (PFGE) on Flavobacterium columnare, to use PFGE to characterize F. columnare channel catfish isolates, and to determine whether variation in pathogenic potential exists in F. columnare isolates from channel catfish. Methods and Results: On the basis of PFGE-derived profiles, similarity dendrograms constructed for more than 30 F. columnare isolates showed two major genetic groups with more than 60% similarity. Channel catfish fingerlings challenged with PFGE group A isolates by bath immersion had significantly higher average mortalities (>60%) than fish challenged with PFGE group B isolates (<9%). However, abrasion and skin mucus removal made channel catfish fingerlings susceptible to disease caused by group B isolates following immersion exposure. Conclusion: Our results suggest that two genetic divisions of F. columnare channel catfish isolates exist, and that isolates in PFGE group A isolates tend to be more pathogenic to immunocompetent channel catfish fingerlings than PFGE group B isolates. Significance and Impact of the Study: PFGE is a potentially useful tool for determining whether F. columnare isolates are more likely to be primary or secondary pathogens. Pathogenesis research for columnaris disease in catfish should focus on pathogenic isolates from PFGE group A.     

Novel heme-binding component in the serum of the channel catfish (Ictalurus punctatus)

The serum of the channel catfish (Ictalurus punctatus) was examined for heme- and hemoglobin-binding proteins. Electrophoretic mobility retardation assays failed to detect a hemoglobin-binding material similar to mammalian haptoglobin; however, a heme-binding component (not previously described) was identified in catfish seru. The heme-binding component was purified by gel filtration chromatography; electrophoretic analyses suggested it to be composed of two polypeptide subunits of molecular masses about 115 and 98 kDa. This composition is inconsistent with hemopexin, the known heme-binding serum protein of mammals. Although it was not fully saturated with heme, the catfish component contained detectable heme in normal sera. When complexed by the binding material, heme was used as an iron source by isolates of the bacterial Gram-negative genusAeromonas; the capacity of other bacteria to use the complex was not tested. The physiological function of the catfish heme-binding serum protein is presently not clear.     

Density-independent growth of floodplain river channel catfish Ictalurus punctatus

This study investigated the relative influence of biotic and abiotic factors on the growth of channel catfish Ictalurus punctatus in seven Mississippi floodplain rivers. The results indicate that growth was density-independent, being defined largely by abiotic conditions.