2013 Annual Report
1a.Objectives (from AD-416):
The objective of this cooperative research project is to conduct aquaculture research addressing fish health problems limiting the production of channel catfish, Ictalurus punctatus.
1b.Approach (from AD-416):
All research conducted under this agreement will address practical, production oriented fish health or disease problems facing the farm-raised catfish industry in the southeastern United States and will address components of the USDA-ARS action plan for National Program 106-Aquaculture. Research projects will be conducted using pond and laboratory facilities at the Delta Research and Extension Center (National Warmwater Aquaculture Center, Stoneville, MS). These facilities are under the direction of the Mississippi Agricultural and Forestry Experiment Station (MAFES) and Mississippi State University College of Veterinary Medicine (CVM). Research will address problems in the following broad subject areas: fish health management, fish diagnostics, epidemiology, and risk assessment modeling. On-farm demonstration projects, scientific articles, technical bulletins and educational workshops will be used to disseminate information to stakeholders.
This project addresses priority issues for augmenting fish health, production efficiency and profitability of commercial catfish farming. A mechanized system for mixing and delivering a live attenuated oral vaccine against enteric septicemia of catfish (ESC) was developed in collaboration with USDA-ARS Poultry Unit and Mississippi State University. Protocols for the commercial production of the vaccine were developed in collaboration with USDA-ARS-National Biological Control Laboratory. Vaccine was fermented in a 50 L floor model commercial fermentor, concentrated and frozen in 50 ml aliquots and validated for cell viability. Frozen vaccine serials were shown stable and effective for up to 1 year. Vaccine field trials conducted with the developed technologies showed excellent protection from disease and negated the need for medicated feeds to control ESC in pond raised fish. Vaccine serials produced from protocols developed from this project will be used to in commercial field trials to assess field safety and efficacy, environmental fate, and establish proof of concept for the develop vaccine technologies. Smallmouth buffalo (SMB) were evaluated as a biological control for proliferative gill disease which is caused by a myxozoan parasite transmitted by an aquatic oligochaete. In contrast to preliminary studies conducted in simulated pond environments, SMB were not shown to alter benthic oligochaete populations nor reducing myxozoan levels in catfish ponds, as determined by polymerase chain reaction (PCR). As result SMB are no longer recommended for biological control of proliferative gill disease (PGD). Development of real-time PCR assays for catfish pathogens led to the reclassification of Edwardsiella (E.) tarda isolated from pond-raised catfish in the southeastern United States. Archived isolates collected from diseased fish from 2007-2012 and identified biochemically as E. tarda upon initial collection were confirmed by species-specific PCR to be misclassified E. piscicida. Comparisons of gyrB sequences demonstrated greater than 99.6% similarity to the E. piscicida type strains from Europe and Asia, suggesting conspecificity. This supports previous claims from Europe and Asia, suggesting a cosmopolitan distribution of E. piscicida and a greater association with disease outbreaks in fish than E. tarda. In addition, PCR assays for E. tarda and a genetic variant of E. piscicida were also developed. This is the first report of E. piscicida in the United States. Quantitative polymerase chain reaction assays for the detection and quantification of Aeromonas hydrophila, Edwardsiella ictaluri, Bolbophorus damnificus, Bolbophorus type II sp., and Henneguya ictaluri have been developed and validated. Similar assays for Flavobacterium columnare, Edwardsiella tarda, Edwardsiella piscicida and Edwardsiella piscicida-like bacteria are in the final stages of validation. These assays provide a reliable method for the detection and quantification of pathogens in pond environments and are being used for rapid diagnostic evaluations and evaluation of treatment efficacies associated with recommended disease management strategies and research. Pharmacokinetic studies of florfenicol in catfish have been conducted to extend label claims for the use of Aquaflor® in catfish. Final study reports from a florfenicol pharmacokinetic study in catfish and minimal inhibitory concentration (MIC) studies were submitted to USFDA for approval of Aquaflor® for control of mortality associated with Aeromonas hydrophila and Edwardsiella tarda in catfish. Botulism Type E was identified as the causative agent of visceral toxicosis of catfish (VTC). Solid phase ELISA assays for the detection of anti-botulism type E toxin were developed against recombinant peptide sequences of the heavy chain botulinum type E toxin (BoNT/E). Antibody from convalescent fish showed low specificity to the peptide sequences employed in the assay. Fish immunized with a recombinant heavy chain (BoNT/E) yielded weak and negligible antibody responses and offered no protection following exposure to the toxin. BoNT/E heavy chain was successfully inserted in channel catfish virus (CCV) and the recombinant BoNT/E CCV will be evaluated as a potential vaccine. Mycotoxin research with channel catfish continued with an evaluation of the effects that cyclopiazonic acid (CPA) has on young catfish. CPA is a mycotoxin produced by Aspergillus flavus the same fungal organism that produces aflatoxin. CPA often appears in sample lots of field corn associated with aflatoxin. After 10 weeks feeding diets containing different levels of CPA contaminated corn in a practical soybean meal-corn basal diet, the fish were challenged with the catfish pathogenic bacterium Edwardsiella ictaluri. Results of the challenge were inconclusive. It is hoped to repeat the experiment at a future date if CPA contaminated corn is available. The Aquatic Research & Diagnostic Laboratory (ARDL), administered by the Mississippi State University’s College of Veterinary Medicine provided comprehensive disease diagnostic service to catfish producers centered in Mississippi and surrounding states, including Alabama, Arkansas, Louisiana, and Texas. In 2012, the ARDL received a total of 635 producer submitted cases diagnostic cases from 41 different commercial farms. It also provided water quality analysis for the 1,332 samples from 119 farms. Bacterial cases dominated the case submissions with 185 Columnaris disease cases and 165 Enteric Septicemia of Catfish cases. Unlike the previous year, no cases of the highly virulent Aeromonas hydrophilia cases were seen at the laboratory. Also no antibiotic resistant bacterial isolates were seen last year. There was an increase in the number of Bolbophorus trematode cases in 2012 and this upsurge appears to have continued in 2013. Increased pressure from the American white pelican has resulted in wide spread debilitating trematode infections on a majority of farms. Disease treatment regiments, developed from this project, have been implemented and shown effective in controlling the intermediate host of the parasite. Hybrid catfish case submissions also increased corresponding to the expanded use of hybrid catfish by the industry.