Streptococcus iniae causes streptococcosis, the most important bacterial disease affecting Australian farmed barramundi. Streptococcosis is a major limiting factor in production of barramundi in freshwater and marine systems. Economic loss occurs through high mortalities, loss of marketable product, lost feed costs and costs of treatment, control, prevention and cleanup. Eradication of the disease from the farm environment is not possible. Vaccination offers an inexpensive, reliable and safe method of preventing the disease; however, current strategies rely on autogenous vaccines, i.e., vaccines prepared from specific strains of the organisms causing disease on a particular farm. Provision for preventative vaccination of stock is currently hampered by the lack of a commercially licensed generic Streptococcus vaccine. Further, the use of autogenous vaccines does not protect the fish from disease caused by newly emergent strains and the reproduction of vaccines in response to each separate occurrence is time consuming. At least seven strains of S.iniae are recognised in Australia, with further strains likely to emerge. Current vaccines are strain specific and therefore cross protection against all isolates in all locations in Australia may not be afforded. It has been demonstrated on at least one occasion in Darwin that a vaccine developed against one strain was ineffective against another. A need exists to: Understand the underlying molecular mechanisms whereby new strains of S.iniae evolve; develop technologies that will provide rapid typing of existing or new strains of S.iniae and; provide a strategy for rapid incorporation of new strains into a polyvalent vaccine for national industry use.