David J. Wise

The epidemiology of bacterial diseases in food-size channel catfish.

Enteric septicemia of catfish (ESC) and columnaris are the most economically important bacterial diseases affecting the channel catfish Ictalurus punctatus industry in the United States. Although these two diseases have been extensively researched, little is known about their prevalence and epidemiology in production systems. In 1997, a two-part survey of catfish producers in Alabama, Arkansas, Louisiana, and Mississippi was conducted to estimate the proportion of ponds and catfish operations that have these diseases and to develop information on the risk factors associated with reporting an occurrence. The response rates to the two phases of the survey were 65.6% and 75.3%, respectively. Overall, 78.1% of all operations and 42.1% of all ponds experienced problems with ESC/columnaris. Higher percentages of large operations and ponds on large operations experienced these problems. The most frequently reported average loss per outbreak of the two diseases was 200-2,000 lb (1 lb = 0.454 kg) per outbreak. Univariate analysis and multivariable regression modeling of the survey data identified three possible risk factors associated with ESC/columnaris, namely, operation size, stocking density, and feeding rate. Conversely, operations that produced their own fingerlings and those that drained ponds at intervals of 3 years or less were less likely to report losses. The associations identified in this study do not establish firm causal relationships, but they do generate hypotheses about managerial and environmental interactions that represent substantial risks to production.

Effects of Dietary Selenium and Vitamin E on Red Blood Cell Peroxidation, Glutathione Peroxidase Activity, and Macrophage Superoxide Anion Production in Channel Catfish

Abstract Fingerling channel catfish Ictalurus punctatus were fed purified diets either unsupplemented and deficient in both selenium and vitamin E, deficient in either selenium or vitamin E, adequate in both selenium (0.2 mg/kg) and vitamin E (60 mg/kg), or excessive in both nutrients (four times the recommended levels). After 115–120 d of feeding the experimental diets, the red blood cell membranes offish fed diets deficient in vitamin E were more susceptible to peroxidation than were those of fish fed diets that met or exceeded vitamin E recommendations. Hepatic, selenium-dependent glutathione peroxidase activity was suppressed in fish fed diets deficient in selenium when compared with this enzyme activity in fish fed diets containing recommended or higher levels of selenium. Intracellular superoxide anion production of macrophages was higher in fish fed the diet fortified with four times the recommended levels of both nutrients than in fish fed the other diets. None of the results indicated that seleni...

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 vi...

Effects of Stress on Susceptibility of Naive Channel Catfish in Immersion Challenge with Edwardsiella ictaluri

Abstract The effects of stress on the susceptibility of fingerlings of channel catfish Ictalurus punctatus to Edwardsiella ictaluri during immersion challenges were evaluated. Channel catfish fingerlings were exposed to a standardized confinement stressor for 30 min. Infections were established in stressed and nonstressed channel catfish fingerlings by exposure to E. ictaluri under aerated static conditions for 24 or 48 h. Stress and increased time of static bacterial exposure significantly decreased the survival of channel catfish fingerlings after immersion challenge. This study established a relationship between a behavioral stressor (confinement) and increased susceptibility of channel catfish to E. ictaluri infection. From estimates ofexperimental error, a relationship between the precision of the challenge system and the number of replicate aquaria per treatment was established. This analysis indicated that the immersion challenge is associated with a high degree of variability, which limits the eff...

IncA/C Plasmid-Mediated Florfenicol Resistance in the Catfish Pathogen Edwardsiella ictaluri

Florfenicol (FFC) has recently been approved by the Food and Drug Administration for the treatment of several bacterial diseases of cultured fish species in the United States, including enteric septicemia of catfish (ESC) caused by Edwardsiella ictaluri. The FFC-resistant E. ictaluri strain (M07-1) described herein was isolated from a moribund catfish obtained from the Thad Cochran National Warmwater Aquaculture Research Center (Stoneville, MS) in May of 2007 and was confirmed to be E. ictaluri by 16S rRNA gene sequencing (6). Fish showing signs of ESC were examined for FFC-resistant E. ictaluri because losses due to ESC persisted in this population despite FFC treatment. To characterize the resistance properties of this strain, conjugative transfer experiments were performed as described previously (14) using FFC (30 μg/ml) for selection. The antimicrobial susceptibilities of M07-1, the corresponding FFC-resistant transconjugant, and the isogenic parent strain (Table ​(Table1)1) were quantified using standard microdilution assays (3, 4, 11), demonstrating that the resistance phenotype observed in strain M07-1 was self-transmissible, conferring resistance to FFC, chloramphenicol, tetracycline, streptomycin, ampicillin, amoxicillin-clavulanic acid, ceftiofur, and cefoxitin, as well as decreased susceptibility to trimethoprim-sulfamethoxazole and ceftriaxone. Resistance transfer correlated to a 150-kb plasmid (referred to hereinafter as pM07-1), suggesting the presence of a multidrug resistance plasmid in this isolate (data not shown). PCR analysis (15) followed by sequencing confirmed that E. ictaluri M07-1 and its multidrug-resistant (MDR) transconjugant harbored the floR gene.

Bolbophorus confusus Infections in Channel Catfish in Northwestern Mississippi and Effects of Water Temperature on Emergence of Cercariae from Infected Snails

Abstract The digenetic trematode tentatively identified as Bolbophorus confusus has recently been implicated as a cause of severe mortalities and reduced production in commercially raised catfish in the lower Mississippi Valley. Our study documents the prevalence of B. confusus infections in channel catfish Ictalurus punctatus from fish farms located in northwestern Mississippi. As of August 2000, 821 ponds had been sampled (approximately 20–40 fish per pond) from 32 farms in eight Mississippi counties. Of these ponds, 262 yielded at least one fish with metacercariae characteristic of B. confusus. The overall impact on farms and the industry cannot be fully evaluated from these data, but evidence suggests that infection with this trematode is becoming widespread, with the more severely affected farms being in close proximity to pelican roosting or resting sites. To evaluate some of the long-term implications of this trematode for farm management, two laboratory studies were conducted to determine the rela...

15 Health management

Publisher Summary Channel catfish health management begins with creating and maintaining a proper living environment for the fish. Good management also includes the design and operation of a production facility that minimizes the impact of stress on the fish. To promote health and minimize stress, fish should be provided with their basic needs: sufficient space, good water quality, a nutritionally complete diet, limited physical disturbance, protection from predators, and prudent handling. Once these needs are met, it is important to limit contact with disease-causing agents and to prevent environmental deterioration. Even in well-designed and properly managed facilities, it is not uncommon for diseases to occur. Once a disease outbreak ensues, effective health management requires three basic steps: problem identification, diagnosis, and corrective management—all of which must be performed in a timely manner to avoid further losses. Whenever multiple factors contribute to the disease process, it makes the diagnosis more difficult and often complicates corrective management. Many fish health problems, such as oxygen depletions, can be recognized and corrected by the fish culturist on the pond bank. This chapter discusses factors affecting the disease process in catfish and steps that can be taken to diagnose disease problems. The chapter provides an overview of the various options for managing infectious diseases. Several specific management procedures for the important catfish diseases are also discussed.

Application of a real-time PCR assay for the detection of Henneguya ictaluri in commercial channel catfish ponds

Proliferative gill disease (PGD) in channel catfish Ictalurus punctatus is caused by the myxozoan parasite Henneguya ictaluri. Prolonged exposure of channel catfish to the actinospore stage of the parasite results in extensive gill damage, leading to reduced production and significant mortality in commercial operations. A H. ictaluri-specific real-time (Q)PCR assay was used to determine parasite levels in commercial channel catfish ponds and evaluate the risk of losing fish newly stocked into the system. Previous research has shown the H. ictaluri actinospore to be infective for approximately 24 h; therefore, determining the parasite load (ratio of parasite DNA to host DNA) in sentinel fish exposed for 2 separate 24 h periods with a minimum of 1 wk between sampling indirectly represents the rate at which infective actinospores are being released by the oligochaete host and if that rate is changing over time. Alternatively, QPCR analysis of pond water samples eliminates the need for sentinel fish. Water samples collected on 2 separate days, with a minimum of 1 wk between sampling, not only determines the approximate concentrations of actinospores in the pond but if these concentrations are remaining stable. Increases in parasite load (r = 0.69, p = 0.054) correlated with percent mortality in sentinel fish, as did increases in mean actinospore concentrations (r = 0.63, p = 0.003). Both applications are more rapid than current protocols for evaluating the PGD status of a catfish pond and identified actinospore levels that correlate to both high and low risk of fish loss.

Genetic Sequence Data Identifies the Cercaria of Drepanocephalus spathans (Digenea: Echinostomatidae), A Parasite of the Double-Crested Cormorant (Phalacrocorax auritus), with Notes on its Pathology in Juvenile Channel Catfish (Ictalurus punctatus)

Abstract: An unidentified xiphidio-type cercaria, previously thought inconsequential to catfish health, was found to be released from marsh rams-horn snails (Planorbella trivolvis) inhabiting ponds on a commercial catfish operation in the Mississippi Delta. A preliminary challenge of cohabiting channel catfish (Ictalurus punctatus) with snails actively shedding the unidentified cercariae resulted in death of some fish. A second cohabitation trial yielded similar results, as did a third challenge of 250 cercariae/fish. Histopathology revealed developing metacercariae concentrated in the cranial region, especially within the branchial chamber, with several metacercariae at the base of the branchial arches within, or adjacent to, blood vessels, possibly the proximate cause of death. Genetic sequence analysis of the 18S small subunit ribosomal DNA (ssDNA), 28S large subunit rDNA (lsDNA), and cytochrome oxidase (Cox1) genes all matched the cercariae to Drepanocephalus spathans (Digenea: Echinostomatidae), a parasite of the double-crested cormorant (Phalacrocorax auritus), a piscivorous bird endemic on most catfish farms. This is the first commentary regarding pathology of D. spathans in juvenile channel catfish as well as the first report of the marsh rams-horn snail as an intermediate host in the D. spathans life cycle. The data presented here suggest this parasite could have limiting effects on catfish production, further supporting the need for adequate snail control programs to reduce trematode prevalence on commercial catfish operations.

Effect of Sublethal Exposure to the Trematode Bolbophorus spp. on the Severity of Enteric Septicemia of Catfish inChannel Catfish Fingerlings

Abstract The digenetic trematode Bolbophorus damnificus has been implicated as a cause of mortalities and reduced production in farmed channel catfish Ictalurus punctatus in northwestern Mississippi. Field observations indicate that infection can exacerbate losses from common bacterial diseases, such as enteric septicemia of catfish (ESC), which is caused by Edwardsiella ictaluri. The interaction of concurrent infections with Bolbophorus spp. and E. ictaluri was investigated using three replicates of four experimental treatments. Trematode infections were established by placing fingerlings for 24 h in triplicate static tanks containing marsh rams-horn snails Planorbella trivolvis shedding Bolbophorus cercariae at a rate of 770 ± 82 (mean ± SE) per 24-h period. Unexposed fish were maintained in three tanks under similar conditions. From each tank, trematode-infected or noninfected fish were transferred to six aquaria (30 fish/aquarium). Three aquaria from each replicate treatment tank received 7.5 × 105 co...