Location: Warmwater Aquaculture Research Unit
2017 Annual Report
Objectives
1) Investigate new and emerging diseases, and develop rapid diagnostic procedures for important pathogens of channel, hybrids and blue catfish.
Subobjective 1.1 Use diagnostic case submissions to identify changes in disease prevalence and emergence of new diseases.
Subobjective 1.2 Develop molecular diagnostic tests for simultaneous detection of multiple catfish pathogens.
This objective is non-hypothesis driven and serves as an essential component of the disease surveillance programs and helps define clinical and applied research programs that address critical fish health issues facing the catfish industry.
This research will aim to determine whether molecular markers can be used to identify multiple pathogens in a single PCR reaction.
2) Study the pathology and epidemiology of significant pathogens affecting cultured catfish.
Subobjective 2.1 Evaluate the susceptibility and pathology of catfish to Edwardsiella spp.
Subobjective 2.2 Evaluate the pathology of Drepanocephalus spathans in channel catfish.
This research will determine whether blue, channel, and blue x channel catfish hybrids have varying degrees of susceptibility to Edwardsiella tarda, Edwardsiella piscicida, and Edwardsiella piscicida–like spp and determine whether the metacercariae stage of the digenetic trematode Drepanocephalus spathans is short lived (< 6 months) in channel catfish.
3) Investigate the responses of channel, hybrid and blue catfish to therapeutic agents and oral vaccines for important bacterial pathogens.
Subobjective 3.1 Evaluate susceptibility of archived and clinical bacterial isolates to antimicrobials, and correlate antimicrobial susceptibility with treatment efficacy.
Sub-objective 3.2 Determine the optimal age for vaccinating catfish against ESC using an oral attenuated E. ictaluri vaccine.
Subobjective 3.3 Determine if certain stressors will affect vaccine efficacy and safety of catfish orally vaccinated with an attenuated ESC vaccine.
Subobjective 3.4 Evaluate mortality resulting from exposure of vaccinated fish to archived and year-end E. ictaluri isolates.
Data will establish uniform standardized interpretive criteria that can be used by all aquatic laboratories that are involved with clinical disease diagnosis of catfish. The research will also examine whether antimicrobial susceptibilities determined by minimum inhibitory concentration and zone diameters of inhibition will affect the treatment efficacy of medicated feeds.
4) Develop and implement practical management strategies to improve fish health and production efficiency.
Subobjective 4.1 Evaluate effects of hybrid catfish production on incidence and prevalence of Henneguya ictaluri in catfish ponds.
Subobjective 4.2 Field evaluation of an oral ESC vaccination platform for control of E. ictaluri infections in catfish.
This research will determine if the production of hybrid catfish reduces the incidence and severity of proliferative gill disease, caused by the myxozoan parasite H. ictaluri, in catfish ponds and whether oral vaccination will improve survival and production efficiency of channel catfish raised under commercial conditions.
Approach
Diagnostic records provide critical insight to changes in disease trends and emergence of new diseases affecting animal production systems, an essential component of population health management. This information provides clinicians, caregivers and researchers a good cross-section of disease occurrence across the industry. This information can then be used to prioritize the allocation of resources in the development of rapid diagnostic procedures, disease surveillance and treatment programs and implementation of biosecurity measures to stop the spread of emerging diseases when possible.
Edwardsiella tarda has been identified as an emerging disease as indicated by diagnostic case submissions and interaction with industry advisory groups. Recently, E. tarda has undergone a reclassification, suggesting many organisms previously thought to be E. tarda are actually E. piscicida, a newly described fish pathogen closely related to E. ictaluri. Research will focus on the comparative susceptibility of channel catfish, blue catfish and hybrid catfish to E. piscicida, E. tarda and the as yet classified E. piscicida-like sp. In addition, quantitative PCR assays will be developed to detect and quantify these various pathogens in fish tissues and the pond environment.
Non-hypothesis driven clinical research will be conducted to define minimum inhibitory concentration (MIC) and cut-off values for clinical bacterial pathogens against 3 commercially available antimicrobials. This information is critical to policy review concerning antibiotic approval in the catfish industry. Separately, hypothesis-driven research will be conducted to optimize the effectiveness of oral vaccination and determine environmental factors which may limit efficacy and safety.
Field studies will be conducted to evaluate practical management strategies for controlling two diseases which account for more than half of the diagnostic case submissions to the Aquatic Research and Diagnostic Laboratory (ARDL). Research will focus on development management strategies for controlling proliferative gill disease, caused by the myxozoan parasite Henneguya ictaluri and field evaluation of an oral vaccine for control of enteric septicemia of catfish (ESC) caused by the gram-negative bacteria Edwardsiella ictaluri. These management approaches have the potential to greatly reduce the impact of these diseases, that are estimated to cost the catfish industry $60-80 million annually.
Progress Report
The Aquatic Research and Diagnostic Laboratory (ARDL), which provides services to producers as well as fish health and production researchers in southeastern United States received 744 case submissions in 2016. There were 631 producer cases and 113 cases submitted by United States Department of Agriculture (USDA) and university researchers. The bacterial diseases represented the majority of the submissions with 303 Columnaris disease and 292 Enteric Septicemia Disease cases. There were also 51 Edwardsiella (E.) tarda cases that were molecularly confirmed as E. piscicida, with the majority of these cases from hybrid catfish. There were also 4 Yersinia (Y.) ruckeri cases in 2016 and 5 cases in 2017. Data obtained from case submissions indicates E. piscicida is an emerging disease in the catfish industry with apparent preference towards hybrid catfish. In addition, the occurrence of Y. ruckeri, a rarely reported disease of catfish, has initiated research to determine the significance of these reports. This information has been captured in the end-of-year report which will be published in the upcoming Thad Cochran National Warmwater Aquaculture Center Newsletter.
Research was conducted evaluating the relative susceptibility channel, blue and channel x blue hybrid catfish to Edwardsiella species (spp.) in laboratory challenges. Exposure of catfish to E. tarda and E. anguillarum resulted in negligible mortality indicating these bacterial species are of little concern to catfish aquaculture. Differential susceptibilities were observed in channel and hybrid catfish exposed to E. ictaluri and E. piscicida. Hybrid catfish were shown more susceptible to E. piscicida infection compared to channel catfish but channel catfish were shown more susceptible to E. ictaluri infection compared to hybrid catfish. Research supports diagnostic case submissions suggesting E. piscicida is an emerging pathogen in hybrid catfish. The pathogenesis of a digenetic trematode, Drepanocephalus auritus (formerly D. spathans) was evaluated as another potential emerging pathogen. The cercariae of D. auritus were shown to infect juvenile catfish. The developing metacercariae concentrated in the cranial regions, often occluding blood vessels at the base of the branchial arch, occasionally resulting in death. The infection, however, appears short lived as metacercariae rarely persisted longer than 2 months. Moreover, mortality is negligible after the acute stages of infection (less than 5 days after challenge).
Laboratory vaccination trials were conducted to evaluate factors potentially influencing efficacy and safety. Low oxygen stress before and after vaccination did not decrease efficacy or safety. Vaccine efficacy was also evaluated against archived E. ictaluri isolates obtained from diagnostic case submissions. Vaccination was effective against all isolates evaluated, supporting molecular analysis showing no genetic variation between these isolates. The vaccine was also effective in protecting catfish against infection by E. piscicida, an emerging disease in hybrid catfish. These results were presented at scientific meetings and to producer groups and were used to develop effective and safe vaccination protocols for control of E. ictaluri and E. piscicida infections in commercially raised catfish.
Field trials were conducted under the authority of the Mississippi State Veterinarian and valid veterinarian-client relationships to evaluate oral vaccination protocols and vaccine efficacy. Trials were conducted on 4 commercial farms involving 91 ponds stocked with approximately 80 million channel or hybrid catfish. These trials validated modifications to the vaccine delivery system used to prepare and deliver vaccine- infused feed. Significant improvements in survival, growth efficiency and value were observed in vaccinated fish. Vaccination was shown in increase fish crop value between $1,800 and $2,500 per acre. Meetings with potential commercial partners and industry producer groups have been initiated to develop a strategy for commercialization with the goal of releasing the vaccine in 2018.
Accomplishments
1. A novel vaccine against Enteric Septicemia of catfish. Enteric septicemia of catfish (ESC) is the one of the most problematic bacterial diseases affecting the production of channel catfish fingerlings. Mississippi State University scientists at Stoneville, Mississippi, have developed an effective vaccine and method of oral delivery against this disease. To date, approximately 180 million stocked catfish have been orally vaccinated using the developed technologies in field trials on commercial farms. Improved survival of vaccinated catfish increased the average value of farm production by $1,800-$2,500 per acre. Commercialization strategies are being developed with the goal of releasing the patented vaccine and vaccine delivery system by 2018 and therefore dramatically increase the profitability of catfish farming.
2. Rotation of channel and hybrid catfish in ponds reduces occurrence of disease. Infections of the parasite Henneguya (H.) ictaluri lead to Proliferative Gill Disease (PGD) in channel catfish and significant losses to producers. Mississippi State University research previously found that channel x blue hybrid catfish were a dead end host in the H. ictaluri life cycle, thus preventing propagation of this parasite in ponds. A three year study by ARS scientists at Stoneville, Mississippi, demonstrated significant reduction in H. ictaluri numbers and incidence of PGD reduced in channel catfish grown in ponds that had previously contained hybrid catfish, rather than channel catfish, through a production cycle. These results have led to field trials on commercial catfish operations as a method of reducing losses associated with PGD. This data has been presented at scientific meetings and producer workshops.
Review Publications
Reichley, S.R., Waldbieser, G.C., Lawrence, M.L., Griffin, M.J. 2016. Complete genome sequence of Edwardsiella hoshinae ATCC 35051. Genome Announcements. doi:10.1128/genomeA.01605-16.
Tekedar, H.C., Kumru, S., Kalindamar, S., Karsi, A., Waldbieser, G.C., Sonstegard, T.S., Schroeder, S.G., Liles, M.R., Griffin, M.J., Lawrence, M.L. 2017. Draft genome sequences of three Aeromonas hybrophila isolates from catfish and tilapia. Genome Announcements. 5:e01509-e01516.
Tekedar, H., Kumru, S., Karsi, A., Waldbieser, G.C., Sonstegard, T.S., Schroeder, S.G., Liles, M., Griffin, M., Lawrence, M. 2016. Draft genome sequences of four virulent aeromonas hydrophila strains from catfish aquaculture. Genome Announcements. 4:e00860-16.
Rosser, T.G., Griffin, M.J., Quiniou, S., Alberson, N.R., Woodyard, E.T., Mischke, C.C., Greenway, T.E., Wise, D.J., Pote, L.M. 2016. Myxobolus ictiobus n. sp. and Myxobolus minutus n. sp. (Cnidaria: Myxobolidae) from the gills of the smallmouth buffalo Ictiobus bubalus Rafinesque (Cypriniformes: Castostomidae). Systematic Parasitology. 93(6):565-574.
Griffin, M.J., Reichley, S.R., Greenway, T.E., Quiniou, S., Ware, C., Gao, D.X., Gaunt, P.S., Yanoung, R.E., Pouder, D.B., Hawke, J.P., Soto, E. 2016. Comparison of Edwardsiella ictaluri isolates from different hosts and geographic origins. Journal of Fish Diseases. 39:(8)947-969.
