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Enteric Redmouth (ERM) VaccinationEver wonder whether the ERM vaccine used on your fingerling fish has helped to protect them against an outbreak of redmouth?? Chances are good that it has if properly administered in the first place. However, there are limitations to the effects of proper vaccination. The following are several factors which could affect the vaccination. Factor 1: Temperature. The most common problem encountered in administering the ERM bacterin (vaccine) is a tendency to attempt the process when the water is too cold. The following table illustrates the time necessary for rainbow trout to develop maximum immune resistance against ERM at varying temperatures. ______________________________________________________
Too often, the tendency is to rush to get the fingerlings outside in the spring, potentially exposing them to the live bacteria before the vaccine has had a chance to work. Even if an acute outbreak of the disease does not occur immediately, the result may the development of "carrier" fish that harbor the live bacteria only to reinfect the group and others at a later time. A good technique to practice is to vaccinate after the water temperature is at least 50 OF, then hold the fish inside or away from possible exposure to the ERM bacteria for at least two weeks. Factor 2: Fish Size. Just remember that the smaller the fish when vaccinating (up to between 100 - 200/pound), the shorter the duration of protection. Typically, between 85% and 100% of trout vaccinated will survive a challenge with live bacteria thirty days after vaccination. To decline to a 50% level of protection (50% survival to challenge) takes approximately 180 days if the fish were smaller than 500/pound, 250 days if the fish were 400/pound, about 300 days at 300/pound, and over a year if they were larger than 200/pound. Obviously, a 50% mortality is less than desirable, so a booster application might be advisable if the fish are going to be kept for longer than 300 days, the point at which the immune response from vaccination begins to decline rapidly. Factor 3: Concentration and Application Method. Remember the saying "when all else fails, read the directions"?!? To obtain a good immune response from the ERM vaccine, it is essential to expose the fish to an adequate quantity of the bacterin for the minimum exposure time. The manufacturer has provided instructions with the vaccine based upon the concentration of killed bacteria in the vaccine. If you choose to administer the vaccine by an alternate method, it very likely will not work. Diluting the vaccine by trying to "stretch" the weight of fish exposed to a single batch, or by adding the vaccine to too large a volume of water (such as in a hauling tank) is not advisable for the initial vaccination process. The simple fact is that the fish will not take up an adequate concentration of the bacterin into their system. A dilute exposure is suggested as a method of "boosting" the effect several months later, if required. Request information on appropriate booster concentrations from the vaccine supplier. Factor 4: Take an Active Fish Health Management Approach. Consider the length of time the fish are protected by the vaccine, then consider what your target market size is for the fish and work backward. If it takes 350 days for your fish to reach market size, and the vaccine provides maximum protection for only 300 days, then try to hold them for the first 50 days in an area free of ERM, then vaccinate just prior (but at least two weeks) to moving them onto your main production area. An alternative for persons who have chronic ERM problems on their farms would be to purchase fish at a large enough size to be able to complete production within 300 days. And make sure they were properly vaccinated two weeks prior to stocking. If the fish are to be grown through more than one growing season, a booster vaccine is advisable. Finally, remember that no vaccine is a substitute for good management of your farm. Always provide the best water quality possible, use proper feeding methods, remove mortalities ASAP, and avoid crowding and any unnecessary stress of the fish.
Written by:Dr. Jeffrey M. Hinshaw Vaccinating Fingerlings Vaccinating rainbow trout fingerlings against Enteric Redmouth (ERM) is effective if done correctly. Applying the vaccine without following the recommendations and understanding the limitations wastes effort and money. The following are some facts and procedures to keep in mind.
There is only one licensed supplier of ERM vaccine in the US:
Injection vaccination equipment can be obtained from:
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