A method for increasing the weight and growth rate of fish, preferably Salmonidae, and for preventing and for treating microbial infections, comprising the steps of a) adding one or more species of probiotic bacteria to water, wherein the species of bacteria comprises or consists of Aliivibrio njordis, Aliivibrio balderis and for Aliivibrio nannie； and b) exposing the fish to the water contairung the one or more species of probiotic bacteria. Preferably, the bacterial strains Aliivibrio njordisstrain Bl-25, 8-l/2013 mandib VII, Aliivibrio balderisBl-24, 18-l/2013 kidn Vl2 and for Aliivibrio nannie B8-24, 313/2013 kidn Vl3 are used.
