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Duplicate groups of Atlantic salmon (Salmo salar L.), kept in seawater, were fed ¢sh meal-based coldpelleted diets. Diets with non-starch polysaccharides (NSP), either cellulose, puri¢ed soybean NSP or extruded puri¢ed soybean NSP at a dietary level of 100 g kg À 1 , were compared with a diet without supplemental NSP and a diet with soybean meal in a 28day feeding trial. Isolation and characterizations were limited to culturable bacteria and population levels of aerobic and facultative aerobic heterotrophic autochthonous (adherent) and allochthonous (transient) bacteria present in the mid and distal intestines of Atlantic salmon fed the ¢ve di¡erent diets estimated using traditional bacteriological techniques. The presence of an autochthonous microbiota was demonstrated using transmission electron microscopy. No signi¢cant e¡ects of diet composition were observed on total population levels of culturable bacteria present in the digestive tract, but the study showed that the composition of the gut microbiota (autochthonous or allochthonous) was sensitive to dietary changes. A total of 752 culturable isolates from the intestines were characterized by biochemical and physiological properties. Of these, 188 isolates were further characterized by partial sequencing the 16S rRNA genes. Among these, 146 isolates belonged to 31 phylotypes that were 494% identical to previously described species. However, 42 isolates showed similarity o94% to species available at the National Center of Biotechnology Information. Several of the phylotypes identi¢ed in the present study have not been reported previously in the gastrointestinal (GI) tract of ¢sh, including the Gram-negative bacteria Gelidibacter salicanalis, Pseudoalteromonas elyakovii, Psychrobacter aquimaris, Psychrobacter cibarius, Psychrobacter fozii, Psychrobacter maritimus, Psychrobacter okhotskensis and Psychrobacter psychrophilus. Among the Gram-positive bacteria identi¢ed were Arthrobacter bergeri, Arthrobacter psychrolactophilus, Arthrobacter rhombi, Bacillus pumilus, Bacillus subtilis, Exiguobacterium spp., Microbacterium oxydans, Planococcus maritimus, Sporosarcina ginsengisoli and several bacteria that have been described as unculturable previously. In addition, we identi¢ed Carnobacterium inhibens, a lactic acid bacterium that is not frequently isolated from the GI tract of ¢sh. Psychrobacter cibarius was the dominant bacterial species and was isolated from the digestive tract of all ¢sh investigated.

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Two experiments were conducted to investigate effects of feed processing conditions and potassium diformate (KDF) supplementation on apparent digestibility of nutrients in Atlantic salmon (Salmo salar) and physical quality of extruded feed. In Exp. 1, diets with raw or expander pretreated full-fat soybean meal (FFSBM) at 100 or 120°C were extruded at 110°C. Expander pretreatment significantly (P < 0.05) improved the digestibility of arginine, glutamine and tyrosine in Atlantic salmon. The higher digestibility of expander pretreated FFSBM was confirmed in mink (Mustela vison). In Exp. 2, diets with defatted soybean meal (SBM) were extruded at 110, 130 or 150°C. The results showed that increasing extrusion temperatures significantly (P < 0.05) improved the digestibility of most major nutrients and amino acids in Atlantic salmon. In general, KDF supplementation to FFSBM and SBM diets did not affect digestibility of nutrients in Atlantic salmon or mink. Expander pretreatment and increasing extrusion temperatures increased pellet expansion, while KDF supplementation reduced pellet expansion.