Responses of Blue Catfish and Channel Catfish to Environmental Nitrite

Abstract

In nitrite-exposure experiments, percent methemoglobin, plasma nitrite concentration, and plasma chloride ion concentration were compared between channel catfish Ictalurus punctatus and blue catfish I. furcatus exposed to sublethal levels of nitrite for 48 h at 25°C. In nitrite-recovery experiments, fish exposed to elevated environmental nitrite for 12 h were transferred to freshwater, and blood characteristics were monitored during the 24-h recovery period. Blue catfish appeared to be more resistant to environmental nitrite than channel catfish. Methemoglobin levels (percent of hemoglobin in methemoglobin form) were significantly lower in blue catfish than in channel catfish. Maximum plasma nitrite concentrations were 137 mg NO₂-/L plasma in blue catfish and 164 mg NO₂-/L plasma in channel catfish. Percent methemoglobin and plasma nitrite concentration were closely correlated. Plasma chloride decreased initially with exposure to nitrite but quickly returned to control levels. Blue catfish exposed to nitrite at 10°C required 1 week to recover when placed in nitrite-free water. The methemoglobin reductase enzyme apparently functioned at a slow rate in fish acclimated to cold temperatures.     

Effect of Vitamin E on the Immune Response of Channel Catfish to Edwardsiella ictaluri

Abstract

Three-month-old fingerling channel catfish Ictalurus punctatus were fed purified diets supplemented with ∝-tocopherol acetate to provide 0, 60, and 2,500 mg vitamin E/kg for 180 d. A 30-s immersion bath and an oral booster were used to deliver a bacterin of formalin-killed Edwardsiella ictaluri to half of the fish from each dietary treatment. Resistance of red blood cells to peroxidation was used as an index of antioxidant status. The susceptibility of red blood cells to oxidative hemolysis decreased with increasing levels of dietary vitamin E. Vaccinated and nonvaccinated fish were evaluated for agglutinating antibody titers and macrophage activity. Humoral antibody titers in response to E. ictaluri were significantly (P ≤ 0.05) higher in vaccinated fish than in nonvaccinated fish; however, no such differences in agglutinating antibody titers were detected among any of the dietary treatment groups. Both vaccination and vitamin E significantly enhanced the ability of macrophages to phagocytize virulent E. ictaluri. Results of this study indicate that elevated levels of dietary vitamin E may affect the ability of channel catfish to respond immunologically to bacterial pathogens.     

Enteric Septicemia Resistance in Blue Catfish and Three Channel Catfish Strains

Abstract

Seven full-sib families in each of three strains of channel catfish Ictalurus punctatus (mean weight, 10.7 g; SD, 2.6 g) and one family of blue catfish I. furcatus (mean, 10.9 g; SD, 0.4 g) were challenged by immersion with the bacterium Edwardsiella ictaluri, the causative agent of enteric septicemia, to evaluate variation in disease resistance. Blue catfish were resistant to infection and had only 0.7% mortality. Significant (P < 0.001) variation in channel catfish resistance was found among strains, families, and body weights. Red River strain channel catfish were the most resistant (14.9% mortality), followed by Mississippi-select fish (67.1%) and Mississippi-normal fish (72.3%). Mean family mortality of channel catfish ranged from 1.3% in a Red River family to 95.3% in a Mississippi-select family. Although weight had a significant effect on survival, the regression slope of survival on weight was ?0.10 (SE, 0.02). Sources of variation in channel catfish mortality adjusted for weight were 67.3% from strains, 29.7% from families, and 3.0% from replicate tanks. The mechanism for differential resistance presently is unknown. Results indicate considerable potential for reducing disease losses by using E. ictaluri-resistant catfish strains in aquaculture and for genetic improvement in resistance via selective breeding programs.     

Subchronic Toxicity of Dietary Aflatoxin B1 to Channel Catfish

Abstract

Means for growth rate, hematocrit, hemoglobin concentration, and erythrocyte count of channel catfish Ictalurus punctatus fed 10,000 μg aflatoxin B₁ (AFB₁) per kilogram of feed for 10 weeks were significantly lower than those of fish fed 2,154 μg/kg or a lower concentration (P < 0.05). Mean leukocyte count was significantly higher in the fish fed the highest concentration of AFB₁ (P < 0.05). Gross appearance and behavior of all fish were normal. Histopathological effects were observed only in fish fed the highest concentration of AFB₁. These fish had foci of necrotic hepatocytes mixed with basophilic hepatocytes. Spaces, apparently resulting from hepatocellular necrosis, were present within the basophilic foci. Sinusoids in the head (hematopoietic) kidney were dilated and circular in profile. Increased hematopoietic activity of blood-forming tissues was apparent from the presence of numerous immature blood cells. The intestinal mucosal epithelium accumulated excessive amounts of iron pigments. Gastric glands in the stomach were necrotic and contained infiltrating macrophages.     

Channel Catfish with a Rayed Adipose Fin

Abstract

Two channel catfish Ictalurus punctatus with rayed adipose fins were found in an aquaculture population. One specimen was radiographed and then cleared enzymatically and stained to demonstrate cartilaginous and calcified portions of the adipose and anal fins. The adipose fin, which had 33 rays (lepidotrichia) and was supported by pterygiophores, was morphologically similar to the anal fin. The cause of the abnormal adipose fin was not determined.     

Susceptibility of Six Bacterial Pathogens of Channel Catfish to Six Antibiotics

Abstract

Two hundred eight bacterial isolates from diseased channel catfish Ictalurus punctatus were screened for susceptibility to apramycin, enrofloxacin, cephalothin, oxytetracycline, sulfadimethoxine-ormetoprim, and tilmicosin by the Kirby-Bauer disk diffusion method. Bacteria evaluated were Edwardsiella ictaluri, E. tarda, Aeromonas sp., A. hydrophila, A. sobria, and Pseudomonas sp. All bacteria were most susceptible to enrofloxacin (99.0%) and apramycin (97.6%), but only 86.5% were susceptible to sulfadimethoxine-ormetoprim, 84.1%o to oxytetracycline, and 75.5% to cephalothin. Edwardsiella ictaluri, E. tarda, A. hydrophila, and A. sobria were 100% susceptible to enrofloxacin. Aeromonas sp., E. ictaluri and E. tarda were 100% susceptible to apramycin. Resistance was detected in all bacterial species to cephalothin, oxytetracycline, sulfadimethoxine-ormetoprim, and tilmicosin. Testing E. ictaluri against sulfadimethoxine-ormetoprim gave larger zones of inhibition on Mueller-Hinton medium than on brain-heart infusion agar.     

Communications: Specificity of the Channel Catfish Antibody to Edwardsiella ictaluri

Abstract

The specificity of channel catfish Ictalurus punctatus serum antibody to Edwardsiella ictaluri was characterized by microtiter agglutination assay. There was no correlation between antibody titer to Aeromonas hydrophila and antibody titer to E. ictaluri in wild or feral channel catfish. Anti-E. ictaluri antibodies in naturally infected channel catfish were not removed by adsorption by nine other species of bacteria found in the channel catfish intestine and fish ponds. Channel catfish immunized with nine other species of bacteria did not develop substantial antibody titer to E. ictaluri. The antibody response of channel catfish to E. ictaluri is highly specific, and the microtiter agglutination test is a specific indicator of previous exposure to E. ictaluri     

Specificity of Humoral Responses of Convalescent Channel Catfish to Edwardsiella ictaluri

Abstract

Serum samples from 15 yearling channel catfish Ictalurus punctatus convalescing after experiencing enteric septicemia of catfish were distributed into three representative serum pools, each containing equal volumes of serum from five fish. Serologic recognition of each pooled serum sample against Edwardsiella ictaluri and Escherichia coli whole cells and against secretory antigen (exoantigen) derived from E. ictaluri was measured by enzyme-linked immunosorbent assays (ELISA). Serum samples were purified by affinity chromatography with a heterologous Ra,-mutant lipopolysaccharide that was derived from rough Salmonella typhimurium TV 119 and was covalently bound to an agarose matrix. Removal of antibodies recognizing the lipopolysaccharide by cross-reactive affinity purification caused significant decreases in serologic recognition of E. ictaluri (P < 0.10) and E. coli (P < 0.01) whole cells; however, serologic recognition of the E. ictaluri-specific exoantigen was not significantly decreased. These results indicate that serologic recognition of the exoantigen is highly specific and that cross-reactive immune responses recognizing homologous gram-negative core antigens will not cause false-positive test results when the specific capture ELISA is used to detect exposure to E. ictaluri     

An Elevated Dietary Level of Ascorbic Acid Fails to Influence the Response of Anterior Kidney Neutrophils to Edwardsiella ictaluri in Channel Catfish

Abstract

Channel catfish Ictalurus punctatus (weight, 320–420 g) were fed diets with 100 or 1,000 mg ascorbic acid/kg of diet for 7 weeks in ponds. Anterior kidney neutrophil function was assessed by incubating the neutrophils with Edwardsiella ictaluri. Percent phagocytosis, phagocytic index (the mean number of bacteria phagocytized per cell by all neutrophils, including nonphagocytic ones), and bactericidal capabilities of the anterior kidney neutrophils were measured at 0, 90, 180, 270, and 360 min. Serum cortisol was also measured. No significant difference was observed between the two diets with respect to anterior kidney neutrophil function or serum cortisol levels. However, serum cortisol levels did affect mean phagocytic index of anterior kidney neutrophils. Catfish that had serum cortisol levels greater than 10 μg/dL displayed a significant decrease in the phagocytic index when compared with catfish that had cortisol levels less than 5 μg/dL.     

Cool Weather Feeding Influences Responses of Channel Catfish to Edwardsiella ictaluri Challenge

Abstract

A pond study was conducted from November 1 through April 30 with young (age-0; average size, 43 g) and market-size (age-2; average size, 660 g) channel catfish Ictalurus punctatus to compare three management regimens: No feeding, partial feeding (no feeding in December, January, and February), and continuous feeding according to fish size and water temperature. Weight change, feed conversion ratio, and responses to experimental challenge with Edwardsiella ictaluri were evaluated. No significant difference in weight gain occurred between partially fed and continuously fed fish in either age-group; average weight increase for fed age-0 fish was 99% and for fed age-2 fish was 38%. The nonfed age-0 fish lost 12.3% and the nonfed age-2 fish lost 7% of their initial weight. Feed conversion ratios were significantly lower in partially fed fish than in continuously fed fish in both age-groups. Mortality from E. ictaluri challenge among age-0 fish was significantly higher in the nonfed fish, but among the age-2 fish, mortality was significantly lower in the nonfed fish. No difference in mortality rate occurred between partially fed and continuously fed fish in either age-group. Starvation induced lower antibody production against E. ictaluri antigen in the age-0 fish but higher antibody production in the age-2 fish. Phagocytic index was lower in nonfed fish than in fed fish from both age-groups. This study indicates no benefit from feeding age-0 and age-2 channel catfish during December, January, or February if feeding is reintroduced in March and continued through April. Although starvation was immunosuppressive in small channel catfish, it enhanced resistance to bacterial infection in larger fish. However, more research information is needed before reduced feeding can be recommended to enhance resistance of channel catfish to E. ictaluri.     

Longevity of Bolbophorus damnificus Infections in Channel Catfish

Abstract

The digenean Bolbophorus damnificus infects commercial channel catfish Ictalurus punctatus, causing mortality, lower feed consumption, and reduced growth in surviving fish. The purpose of this study was to determine the length of time for which B. damnificus prodiplostomulum metacercariae (juvenile trematode stage that infects fish) would remain viable (parasite appearing to be intact or exhibiting movement) in channel catfish. Fish (n = 210) were infected with molecularly confirmed B. damnificus cercariae harvested from naturally infected marsh rams-horn snails Planorbella trivolvis. During the first sampling (at 20 d postinfection), 8.3 ± 3.6 metacercariae/fish (mean ± SD) were found in the host muscle and visceral organs. The channel catfish were then acclimated to a water temperature of either 18°C or 28°C. After 11 months, 6.8 ± 3.5 and 5.9 ± 3.0 metacercariae/fish were found in groups held at 18°C and 28°C, respectively. The mean number of parasites per fish did not significantly differ between fish held at the two temperatures and did not significantly decline over time at either temperature. Fish examined from 13 to 30 months postinfection all contained viable metacercariae that were morphologically and molecularly identified as B. damnificus. At 18 months, 12 metacercariae (of which 11 were intact and 10 displayed movement) were found in the one fish sampled; at 30 months, the last fish sampled contained three intact metacercariae (one displayed slight movement). Our results indicate that B. damnificus metacercariae can remain viable in channel catfish for at least an 18–30-month production cycle during which they have the potential to affect fish growth; in addition, infected fish may serve as intermediate hosts for these metacercariae for at least 2.5 years postinfection.

Received July 14, 2010; accepted March 6, 2011     

Attempts to Control Flexibacter columnaris Epizootics in Pond-Reared Channel Catfish by Vaccination

Abstract

Evaluation of bacterins for the immunization of channel catfish Ictalurus punctatus against Flexibacter columnaris was carried out over 5 years. Groups of 60,000–100,000 pondreared channel catfish, weighing an average of 1.5–4.1 g, were vaccinated each year with formalininactivated Flexibacter columnaris bacterins by immersion. Bacterins were prepared from isolates of the preceding year's epizootic. Equal numbers of nonvaccinated channel catfish reared under similar conditions served as controls. Fish were vaccinated during May each year when water temperatures ranged from 16 to 18°C. Data were recorded daily from early June through midSeptember as water temperatures rose to 24–26°C. Deaths were recorded daily, and the number of hours required for antibiotic treatments were monitored. Analysis of the data indicated a general trend toward a beneficial effect of vaccination, particularly for larger fish. Mortality and hours of antibiotic treatment were significantly higher for most control groups than for vaccinated groups.     

Transmission of Edwardsiella ictaluri from Infected,Dead to Noninfected Channel Catfish

Abstract

Enteric septicemia of catfish (ESC) was transmitted horizontally from channel catfish Icialurus punctatus that had died from Edwardsiella ictaluri infection to contact channel catfish during 2 d of habitation in a tank. The contact channel catfish became positive for E. ictaluri antibody, became infected with this bacterium, and had signs of ESC and died within 12 d postexposure. Edwardsiella ictaluri was recovered from 24 of the 30 contact channel catfish that died from ESC, as well as from 9 of the 25 tested contact survivors. The cannibalizing of E. ictaluri-infected fish, or the shedding of E. ictaluri from dead fish, or both, were shown to be mechanisms of horizontal transmission of ESC among channel catfish.     

Analysis of Short-Term Cortisol Stress Response in Channel Catfish by Anesthetization with Metomidate Hydrochloride and Tricaine Methanesulfonate

The ability of the anesthetics metomidate hydrochloride and tricaine methanesulfonate (MS-222) to mitigate the cortisol stress response of Channel Catfish Ictalurus punctatus was evaluated during a 10-min confinement stress. The cortisol concentrations of Channel Catfish anesthetized in metomidate hydrochloride remained consistent throughout the 10-min exposure; however, for fish anesthetized with MS-222 and nonanesthetized fish, cortisol concentrations were approximately 7- and 22-fold higher, respectively, than the baseline concentrations. While both anesthetics reduced cortisol concentrations relative to those of nonanesthetized fish, these results suggest that MS-222 is an appropriate anesthetic to use during the initial 5 min of sedation and that metomidate hydrochloride is appropriate for longer periods of sedation.

Received November 18, 2014; accepted April 9, 2015     

Immune Response and Resistance of Channel Catfish to Edwardsiella ictaluri Challenge when Fed Various Dietary Levels of Zinc Methionine and Zinc Sulfate

Abstract

The effects of dietary levels of zinc from zinc methionine (ZnM) and zinc sulfate ZnSO₄ on nonspecific immune responses and disease resistance of juvenile channel catfish Ictalurus punctatus (mean initial weight of 3.3 g) were determined. Fish in triplicate aquaria were fed to satiation twice daily for 16 weeks with an egg white basal diet without zinc supplementation or supplemented with 5, 20, and 60 mg zinc/kg as ZnM or 20 and 60 mg zinc/kg as ZnSO₄. Relative percentages of peripheral blood lymphocytes, thrombocytes, and macrophages were not affected by dietary zinc. The relative percentages of neutrophils significantly increased in fish fed 20 and 60 mg Zn/kg as ZnM. Chemotactic responses of macrophages were significantly higher for fish fed the three ZnM-supplemented diets and the 60-mg ZnSO₄. Dietary zinc, however, had no influence on the phagocytic activity of macrophages for Edwardsiella ictaluri. Likewise, neither the source nor the level of dietary zinc provided protection to channel catfish against E. ictaluri. The severity of E. ictaluri infection (number of colony-forming units/g trunk kidney) and the percentage offish that were culture negative for E. ictaluri (15 d postchallenge) were also unaffected by dietary zinc.     

斑点叉尾(鱼回)营养需求和饵料开发研究进展

本文主要综述了近年来国内外对斑点叉尾(鱼回)在营养需求方面的一些研究进展.主要包括蛋白质与氨基酸、脂肪、碳水化合物、维生素与矿物质等需要量的研究进展,人工配合饵料的研制情况.对斑点叉尾(鱼回)在饲料开发方面存在的问题结合我国国情作了一定的分析与讨论,并就斑点叉尾(鱼回)营养和饲料研究对其在我国养殖业中产生的影响作了展望.     

Chemotactic and Chemokinetic Responses of Channel Catfish Macrophages to Exoantigen from Edwardsiella ictaluri

Abstract

The ability of Edwardsiella ictaluri to attract macrophages of channel catfish Ictalurus punctatus was investigated. Exoantigen from E. ictaluri was tested for macrophage chemotactic activities both in vitro and in vivo. The exoantigen was chemotactic and chemokinetic for macrophages in vitro. Peritoneal injection of 750 μg of exoantigen protein into normal (E. ictaluri-free) channel catfish induced a marked increase in macrophage accumulations at 24 and 48 h. Neutrophil accumulation did not occur at the injection sites. Edwardsiella ictaluri exoantigen attracts macrophages, and this attraction may play an important role in macrophage responses during E. ictaluri infections.     

Characterization of Thymidine Kinase Encoded by Channel Catfish Virus

Abstract

The thymidine kinase (TK) encoded by channel catfish virus (CCV) was demonstrated to be biochemically distinguishable from the TK of the host cell line, channel catfish ovary (CCO), as well as from TKs encoded by other herpesviruses. Extracts of CCO cells and of TK-negative CCO cells infected with CCV were assayed for differences in inhibition by deoxynucleosides, in feedback inhibition mediated by thymidine triphosphate (dTTP), and in phosphate donor specificity. Results indicated that, compared with CCO-encoded TK, CCV-encoded TK was more inhibited by deoxypurines and showed less dTTP-mediated feedback inhibition. The CCV-TK was unique among herpesvirus TKs in its inability to utilize CTP as a phosphate donor.     

Decreased Resistance to Edwardsiella ictaluri Infection in Channel Catfish Intraperitoneally Administered an Oil Adjuvant

Abstract

The effects of intraperitoneal injection of squalene, an oil adjuvant, on nonspecific mortality of channel catfish Ictalurus punctatus and on their resistance to experimental Edwardsiella ictaluri infection were studied. Yearling channel catfish were assigned to control (N = 22) or squalene (N = 25) treatment groups, and mortality was monitored for 14 d following treatment. On day 14 both groups were infected with E. ictaluri, the causative agent of enteric septicemia of catfish, and mortality was monitored for an additional 11 d. Before infection, mortality did not differ between groups. After E. ictaluri infection, fish that received squalene were at a substantially higher risk of dying than control fish (relative risk after squalene treatment = 6.86). These results suggest that intraperitoneal administration of squalene, although not directly toxic, decreased resistance to E. ictaluri infection.     

斑点叉尾(鱼回)疑似疱疹病毒感染的病理形态学观察

对四川省一些养殖场斑点又尾鮰大规模死亡的病鱼组织进行了光镜和电镜观察．在其肾和肝组织的细胞中发现一种圆形或椭圆形病毒颗粒，有囊膜的病毒颗粒存在于胞浆中，直径150～200nm．无囊膜的病毒颗粒既存在于胞浆中，也存在于胞棱中，直径为80～110nm，同时在细胞核内可见无病毒核心的空衣壳，根据其形态特征初步确定为一种疱疹病毒。病鱼主要表现为鳍条基部和皮肤（特别是腹部和尾柄）充血、出血，腹部膨大，眼球突出．鳃发白．腹腔内充有淡黄色或淡红色的腹水，胃肠道扩张，其内充满大量淡黄色的粘液，肝、脾和肾肿大。病理组织学变化主要为全身组织器官广泛性水肿、出血、变性、坏死和炎症细胞浸润，特别是肾、肝、胃肠道、脾和脑的损伤较为严重。肾间质水肿，造血组织坏死，巨噬细胞和中性拉细胞浸润．肾小管上皮细胞空泡变性和坏死；肝水肿，狄氏间隙增宽．肝细胞空泡变性及坏死；胃肠道粘膜上皮变性，坏死．脱落，固有膜，粘膜下层水肿，淋巴细胞、巨噬细胞和中性枉细胞浸润；脾淤血．出血．淋巴细胞减少，大量巨噬细胞和中性粒细胞浸润；脑水肿，神经细胞肿胀．甚至坏死固缩。超微结构上．被病毒感染的细胞发生明显的痛变，线粒体肿胀，嵴断裂．溶解，粗面内质网扩张，核糖体颗粒脱落．细胞核体积增大，染色质浓缩．边集。