Inhibition of bacterial fish pathogens by Tetraselmis suecica

Abstract. Supernatants and extracts derived from a commercial heterotrophically grown spray-dried preparation of Tetraselmis suecica were observed to inhibit Aeromonas hydrophila, A. salmonicida, Lactobacillus sp., Serratia liquefaciens, Staphylococcus epidermidis, Vibrio anguillariim, V. salmonicida and Yersinia ruckeri type I, but not Planococcus sp., Pseudomonas fluorescens, Streptococcus sp., V. ordalii or Y. ruckeri type II by in vitro methods. When used as a food supplement, the algal cells inhibited laboratory-induced infections in Atlantic salmon. Moreover, there was a reduction in bacterial numbers in tank water. When used therapcutically, algal cells and their extracts reduced mortalities caused by A, salmonicida, Ser. liquefaciens, V. anguillariim, V. salmonicida and Y. ruckeri type I.