Abstract

Vaccines have been used for many years in terrestrial domestic animals, and, within the past 20 years, more commonly in the salmonid aquaculture industry. The magnitude of economic loss associated with disease outbreaks and limitations on treatments, as well as the cost of vaccine development and cost/benefit of vaccine delivery are just a few important factors that were "tipping points" toward widespread vaccine production and use.

Challenges for Ornamental Species

However, there are many additional challenges to development of vaccines for ornamental aquaculture, and in particular for Florida's ornamental industry. The salmonid industry provided vaccine production companies with a large market for essentially one, highly valued species group. By contrast, ornamental fish producers raise hundreds of species in dozens of families with differing economic values and in a variety of different production scenarios. Vaccines targeting one species or one family have limitations economically for vaccine production companies, especially those interested in developing fully licensed, USDA-approved vaccines. For the short term, then use of autogenous vaccines (vaccines produced from a pathogen derived from the population to be targeted) are perhaps one of the most efficient ways to go. New technologies (e.g., DNA vaccines) are also currently being tested.

Which pathogens should be targeted, and what are potential problems with vaccines for each? There are a number of different pathogens for which ornamental fish vaccines, in theory, might prove more economical than standard post-outbreak treatment. Some important bacterial pathogens include Streptococcus spp., Flavobacterium columnare, Aeromonas salmonicida, Mycobacterium spp., Aeromonas hydrophila complex, Vibrio spp., among others. For some of these, vaccines are in use for various aquacultured food fish species, and for others, vaccines are currently in development. However, the magnitude of differences among strains or closely related species with regard to antigenicity and immunogenicity are cause for concern.

Viral diseases in many species of ornamentals have not been studied well enough to allow vaccine development, but important koi viral diseases which have been studied and/or are of significance include Spring Viremia of Carp and Koi Herpesvirus disease. Each of these has specific issues with regard to use and acceptance of vaccines (including the ability to distinguish vaccinated fish from exposed and potential carriers). Vaccine use against fungal infections or parasitic infestations is perhaps further down the road, although work on some (including against Ichthyophthirius multifiliis) has been ongoing.

Which species or species groups should be targeted? Can a vaccine developed for one species be used effectively in another species or species group? What age classes can be vaccinated? What administration routes are available and practical?

Perhaps most important are questions at the very root of development of a "vaccine mentality." How much will a given vaccine save a producer, do they understand vaccine limitations, and how can benefits be demonstrated? How easily can economic data be collected to justify vaccine development costs? How much does, for example, autogenous vaccine development and production actually cost? And finally, how does a producer effectively integrate vaccine use into an overall fish health management/preventative medicine program?

A "Wet" Run: Streptococcus iniae Autogenous Vaccine Development for Ornamentals

A series of studies to evaluate feasibility and practicality of vaccine development for the industry were carried out from 2001-2004 (Russo, R. University of Florida, Ph.D. Dissertation, 2004). An autogenous vaccine was developed, with funding from USDA-CSREES, and in conjunction with Novartis AquaHealth against Streptococcus iniae isolated from one ornamental production facility in Florida for two species of closely related tropical cyprinids, the rainbow and redtail black sharks (Epalzeorhynchos erythrurus and E. bicolor). The vaccine was effective when administered by IP injection for broodstock (which are also injected for induced spawning, making this a feasible route). Although the vaccine was also effective experimentally in juvenile sharks when administered IP, this route was not practical. Oral and immersion routes did not provide protection. After careful consideration, the producer has opted to continue use in broodstock, despite relatively high cost. As a result of these initial studies, the University of Florida is preparing to continue fostering a "vaccine mentality" among its producers over the next year or two.

Summary

Initial costs for autogenous vaccine production are currently high. The economics of vaccine use in ornamentals still requires careful evaluation. A means to decrease cost/benefit ratios will go a long way toward facilitating further development and use of vaccines in ornamental species. This includes determination of pathogens, fish species and age classes, and proper timing within the production cycle (how early can different species be vaccinated)? For most species, immersion and oral administration are the only feasible routes.