The Disease
Introduction
With the development of intensive fish farming, periodic and epidemic outbreaks of Lactococcosis or Streptococcosis have occurred worldwide. Streptococcosis results from infection of gram-positive cocci, such as the bacterium Lactococcus garvieae. Infection resulting from this bacterium has been noticed in wild and farmed Salmonids and Perciformes (yellowtail, amberjack, sea bream, tilapia, sea bass, horse mackerel, etc) in freshwater and marine environments.
Streptococcosis
One of the most serious diseases of warmwater fish. It is present in both marine and freshwater environments and has a global distribution. Cumulative mortality can be as high as 70%.
Caused by Streptococcus iniae
A Gram-positive, non-acid fast, non motile, oxidase positive, catalase negative, beta-haemolytic, coccus bacterium.
Etiology
The bacterium Lactococcus garvieae is a gram-positive spherical or oval shaped bacteria less than 2 µ m in diameter. Taxonomic studies have shown this coccus to be associated with causative agents of similar diseases classified as Streptococcosis.
Streptococcal disease in fish was first reported in 1957, affecting cultured rainbow trout in Japan (Hoshina, et al. 1958), and has since been determined to effect other fish species including salmon, sea trout, tilapia, sturgeon and striped bass. The disease first appeared in Europe in 1993. With the development of intensive fish farming, periodic outbreaks of Lactococcus garvieae have occurred worldwide.
Other examples of bacterium that have been associated with Streptococcal disease include Streptococcus difficilis, Streptococcus milleri, Streptococcus parauberis, Streptococcus iniae, Lactococcus garvieae, Lactococcus piscium, and Vagococcus salmoninarum (Austin and Austin 1999).
Little is known about the epidemiology of this disease, and investigations have been unable to determine the source of infection; however, it appears that Streptococcosis can be associated with high-efficiency farming methods and conditions of stress infections.
