The present invention relates to veterinary immunology, namely to the immunological response of fish to a virus. More specifically, the invention provides an epitope of salmonid alphaviruses which epitope is capable of inducing a virus neutralising immune response. In particular the invention relates to a polypeptide comprising a certain amino acid sequence, a protein comprising such polypeptide, to a carrier comprising such protein, and to a method of producing antibodies. Further the invention relates to a nucleic acid encoding such polypeptide or such protein, and to a carrier comprising such a nucleic acid. Also, the invention relates to a vaccine and a diagnostic kit comprising such a polypeptide, protein, carrier, or nucleic acid.