The present invention relates to a propyl-methyl-phenol compound, in particular thymol and/or carvacrol or composition comprising a propyl-methyl-phenol compound for use in the treatment and/or prophylaxis of Salmonid rickettsial septicemia (SRS) and/or diseases caused by Piscirickettsia salmonis, and/or for the use in killing, combating or controlling Piscirickettsia salmonis, and for use in the treatment and/or prophylaxis of Infectious salmon anemia (ISA) and/or diseases caused by Infectious salmon anemia virus, and/or for the use in killing, combating or controlling Infectious salmon anemia virus.
