Rainbow trout (Oncorhynchus mykiss) were obtained from the Hanka Taimen OY, Venekoski, Finland.
The fish were fed with a standard commercial feed (Raisio Vextra mini 2.5 mm) at a rate of 2% of the
biomass per day. The fish had not been vaccinated nor exposed to fish diseases and were deemed specific
pathogen free. The fish were acclimated for three weeks in three tanks to laboratory conditions before the
start of the trial. After the acclimation period the average weight of the fish was 83 g and the fish were
randomly divided into six 225 l tanks, each containing 40 fish. The flow rate of the water was approximately
3 l/min. The water temperature was held at 131 (C during the whole trial.
One group served as the control and was fed with unsupplemented feed during the entire trial period. The
other five groups were fed for two weeks (1st and 2nd week) with feed containing different amounts of lactic
acid bacteria (LAB). LAB doses in feed were 7.9104 (LAB4), 2.1106 (LAB6), 2.8108 (LAB8),
1.91010 (LAB10) and 9.71010 (LAB11) bacteria/g of feed, respectively. The feed-rate was 0.7% and 1%
of the biomass during the first week and the second week, respectively. After two weeks of LAB-feeding, the
feeds were changed to un-supplemented feed (3rd and 4th week) and the feed rate was kept at 1% to the end
of the trial.