Location: Aquatic Animal Health Research2011 Annual Report
1a. Objectives (from AD-416)
The objectives of this cooperative research project are to: (1) determine the effectiveness of a modified live Flavobacterium columnare vaccine in reducing mortality of walleye to F. columnare, and (2) determine the age of walleye most effectively vaccinated and the need for a booster vaccination.
1b. Approach (from AD-416)
The Rathbun Fish Hatchery (RFH) produces 200,000 walleye fingerlings (200 mm or larger) for sport fisheries. These fish are produced in a three-phase culture system, corresponding to Phase 1: pond culture of 3 day post hatch fry to 30 days post hatch, final size 45 mm; Phase 2: tank habituation of fingerlings to feed which lasts 30 days, final size 90 mm; and Phase 3: outdoor grow out of fingerlings which lasts 90 days, final size 200 to 250 mm. Columnaris disease, caused by F. columnare, commonly occurs during Phase II culture but also during Phase III. The experimental approach for the first year of study is as follows: At 3 days post hatch (dph), groups of 5000 fry will be vaccinated or sham-vaccinated in triplicate and stocked into ponds for Phase 1 culture. At approximately 30 dph, ponds will be harvested for Phase 2 culture. At pond harvest, each pond will be split into two groups of fingerlings. One group will be sham vaccinated, and the other will be vaccinated. The treatments will consist of: 1. Fry sham vaccinated, fingerling sham vaccinated. (3 replicates) 2. Fry sham vaccinated, fingerlings vaccinated. (3 replicates) 3. Fry vaccinated, fingerling sham vaccinated (3 replicates) 4. Fry vaccinated, fingerlings vaccinated. (3 replicates) For Phase 3 culture, fish will be maintained in the above treatment groups. Several performance variables will be collected to assess the efficacy of the vaccine, including: mortality related to F. columnare (identified by microscope and by re-isolation of F. columnare from kidney samples), survival of walleye at the end of Phase 2 and 3 culture, and growth of walleye at the end of each culture phase. Additionally, blood samples will be collected at the end of Phase 1 culture and at one or more sampling periods during Phase 2 and Phase 3 culture to determine if walleye generated a specific antibody response following vaccination. Pending the results of the first year of study, the research approach will be modified as necessary.
3. Progress Report
A field trial was conducted to determine the effectiveness of a modified live Flavobacterium (F.) columnare vaccine in reducing mortality of walleye due to columnaris disease. Groups of 5,000 walleye fry (~ 3 days post hatch (dph)) were vaccinated or sham-vaccinated in triplicate and stocked into ponds for Phase I pond culture. At approximately 30 dph, ponds were harvested for Phase 2 tank culture. At pond harvest, survival was determined and walleye from each pond were split into two groups of fingerlings. One group was sham vaccinated, and the other was vaccinated. The treatments (3 replicates each) consisted of: (1) fry sham-vaccinated, fingerling sham-vaccinated, (2) fry sham-vaccinated, fingerlings vaccinated, (3) fry vaccinated, fingerling sham-vaccinated, and (4) fry vaccinated, fingerlings vaccinated. Additionally, an internal control group was included, which consisted of triplicate tanks of walleye fingerlings stocked at the same time; these were treated with Diquat when columnaris disease began. This is the procedure used at this facility to control mortality due to columnaris disease. Fish were maintained in the above treatment groups and performance variables were collected to assess the efficacy of the vaccine, including: mortality related to F. columnare, survival of walleye at the end of Phase 2 tank culture, and growth of walleye at the end of Phase 2 tank culture. Flavobacterium columnare was reisolated from mortalities and molecularly characterized by restriction fragment length polymorphism. Serum samples were collected from survivors at the end of the study to measure antibody responses. Survival of the vaccinated and sham-vaccinated fry following Phase 1 pond culture was 82 and 85.9%, respectively. The day following vaccination and stocking the tanks for Phase 2 culture, an acute columnaris epizootic occurred in all tanks and the study was terminated after approximately 40 days. Survival for each treatment group was low (13 to 17%), and there were no significant differences in survival or growth between the treatment groups. Treatment of the walleye fingerlings with Diquat was effective at improving survival from columnaris disease, and the average survival of this internal control group was 64%. The acute columnaris epizootic that occurred following vaccination of the fingerling walleye was atypical for this facility. Columnaris disease typically occurs in fingerling walleye at approximately one week post stocking tanks for Phase 2 culture. Therefore, it is believed that the vaccination/sham-vaccination of the fingerlings likely resulted in stress that increased susceptibility to F. columnare. Twenty-one isolates were obtained from diseased walleye and were determined to be genomovar I. Analysis of serum for specific antibody against F. columnare in survivors is currently in progress. The results from this first field trial will be used to adjust the experimental design for subsequent trials. The project was monitored through numerous phone calls to plan, implement, discuss, and analyze the research results.