U.S. Fish and Wildlife Service, Warm Springs Regional Fish Health Center
Warm Springs, GA, USA
Large Mouth Bass Virus (LMBV) was believed to be first isolated from moribund largemouth bass (Micropterus salmoides) from Santee-Cooper Reservoir in South Carolina in 1995. However, archival samples have shown LMBV was isolated from largemouth bass in four lakes in Florida as early as 1989. Since these early discoveries there have been many reports of LMBV associated with fish kills throughout the southeast and Midwest. The virus has also been isolated from other centrarchid species. It has been suggested that the virus has a predilection for the larger "trophy" size animals and affects the overall population size structure such that the trophy fishery that many anglers seek is severely impacted.
Freshwater bass fishing (black bass) is the most popular type of fishing in the United States with 43% or 12.7 million anglers fishing for them. These anglers spend over 38.4 billion dollars annually participating in this recreational fishing hobby. Because of the potentially huge impact on recreational bass fishing and the significant economic losses that might follow in the local and national economies it is extremely important that fisheries managers establish sound strategies to prevent the spread of this pathogen. In order to develop sound management strategies it is essential that fisheries managers be provided with information on the prevalence and distribution of the virus in wild populations and the overall impact of the virus on population dynamics.
Currently the majority of fish health assessment tools available to fish health professionals require the sacrifice of the animals for sampling. In order to conduct all the sampling necessary it will require the collection of hundreds of samples of various sized animals from hundreds of locations. Certainly the loss of all these animals, due to the lethal nature of our current techniques, should be avoided if at all possible as this is counterproductive for any group or agency dedicated to the conservation and preservation of these animals. To this end the development of rapid non-lethal sampling techniques would allow us to conduct the sampling necessary to carry out this essential disease research while minimizing the number of fish that would be lost.
The use of non-lethal techniques is highly preferred over those requiring that animals be sacrificed for many reasons. For large-scale projects, looking at populations, it is often necessary to sample large numbers of animals to achieve statistically significant numbers. This level of lethal sampling could have long-term effects on the population as a whole, as well as being detrimental to the fishery on the body of water from which the animals are collected. This could lead to economic losses for that area. This type of sampling also makes it impossible to follow individuals or potentially, the population over a time course to determine the effects of the virus within a given animal or population. Lethal sampling also creates public relations problems when the general public is made aware of large numbers of animals being sacrificed or when larger animals are being taken out of the population. These techniques also serve as a focal point for animal rights groups, which are becoming increasingly aware of fishery issues. Additionally lethal sampling is not a pleasant part of any study for the people conducting that study. There are few, if any, fishery managers, biologists, or researchers that enjoy killing the animals they have chosen to devote their careers to advocate. While most of these individuals recognize it is necessary to sacrifice some animals for the greater good of all the animals there is a tremendous preference to use non-lethal techniques whenever possible to spare as many fish as possible. Finally, these techniques may potentially save time, cost less in supplies, and require less expertise, which would make them more cost effective than traditional techniques.
This study evaluated the suitability of non-lethal sampling for the detection of LMBV. Nonlethal samples collected included blood, skin scrape, fin clip, and gill biopsy. These were compared to the standard kidney/spleen samples. All samples were assayed by viral isolation. In addition total white blood cell counts were completed and the presence of anti-LMBV antibodies in the serum was determined by agar gel immuno-diffusion.
Results of this study indicate that a combined sample of a skin scrape, gill biopsy, and fin clip, will detect LMBV in approximately 30% of the animals determined to be infected by using kidney/spleen. None of the other methods evaluated resulted in a high level of viral detection. The data also suggests that the non-lethal techniques are most effective when used within 30 days of initial infection.