Lactococcosis is an emerging pathology affecting a variety of fish species all over the
world. The septicemic processes caused by Gram-positive coccus, commonly
denominated as Streptococcosis, are not new; they were described for the first time
at the end of the 50 s in Japan, where the first cases were diagnosed in the intensive
production of rainbow trout [1]. During the last decade we have noted numerous
changes in the taxonomy of some implied etiological agents that initially were assigned
to the Streptococcus genus. The development of new techniques of diagnosis based on
genotypic characteristics has made possible this reclassification into new bacterial
genera as Enterococcus, Lactococcus, Vagococcus and Carnobacterium [2–5]