The product is a mixture of two monoclonal antibodies (MAbs) directed against Streptococcus iniae. The MAbs have been tested against eight different Streptococcus iniae isolates (Type strains and isolates from disease outbreaks) by ELISA and reacted with all the isolates tested. The specificity of the MAbs has been tested against a range of different bacterial pathogens that infect fish, including Lactococcus garvieae and Enterococcus faecalis, as well as a selection of bacteria found in the aquatic environment. Both MAbs were found to cross-react with Nocardia seriolae in ELISA. This pathogen results in a very different pathology (granuloma formation) in comparison to Streptococcus iniae, enabling positive identification of the bacterium by IHC using Product P11. Both MAbs are of an IgG2a isotype.