Samantekt:
An intervention study was conducted at early juvenile stage of Atlantic cod (Gadus morhua L.) rearing to confirm the properties of two prospective probionts, Arthrobacter sp. and Enterococcus sp. isolated from a cod hatchery. Juveniles (10 g) were fed expanded dry feed for 28 or 55 days, either untreated or treated with the probiotic bacteria in mixture or singly (107–9 CFU g−1 feed). Viability of probionts supplemented to the feed was evaluated during a two-month storage at −20, 4 and 15 °C and sensory evaluation of the probiotic feed performed at the end of storage. Juvenile growth, survival, feed conversion ratio, and microbial load of rearing water, juvenile gills and gut were examined. Microbiological stability of the probionts added to the feed was demonstrated at all temperatures, while sensory evaluation detected faint oxidative off-odours in feed stored frozen. Juveniles fed the Enterococcus-probiotic feed grew significantly faster and had significantly lower gut Vibrio counts than control juveniles (p < 0.05). Overall, the results suggest that both probionts, especially the Enterococcus strain, modified the gut microbiota and contributed to enhanced juvenile growth and survival.