Improved growth and nutrient utilisation in Atlantic salmon (Salmo salar) fed diets containing a bacterial protein meal

Diets containing 0, 4.5, 9, 18 or 36% of a bacterial protein meal (BPM) produced with methane as a carbon source, were fed for 48 days to triplicate groups of Atlantic salmon (initial weight 170 g) in respiration tanks supplied with 12 °C seawater. In addition, a separate 15-day digestibility trial was performed with salmon (initial weight 494 g) fed the 0, 18 and 36% BPM diets. The digestibilities of nitrogen, amino acids, lipid, energy and copper were significantly reduced as the dietary BPM level increased. The specific growth rate (% BW day− 1) in the growth and respiration trial was significantly higher in the 18 and 36% BPM groups (1.59 ± 0.06 and 1.56 ± 0.04, respectively) than in the control and 4.5% BPM groups (1.38 ± 0.06 and 1.37 ± 0.05, respectively). Diet had no effect on feed intake (0.98 ± 0.01% BW day− 1), and although nutrient digestibility was reduced, the feed efficiency ratio was significantly higher in the fish fed 36% BPM (1.54 ± 0.03) than in those fed the control diet (1.39 ± 0.05). The retention of nitrogen was higher in the 9, 18 and 36% BPM groups (52.4 ± 1.1, 52.9 ± 0.8 and 55.1 ± 2.6%, respectively), than in the 0 and 4.5% BPM groups (46.3 ± 1.4 and 45.6 ± 2.0%, respectively), while the energy retention was higher in the 18 and 36% groups (59.1 ± 1.0 and 58.5 ± 2.8%, respectively) than in the control and 4.5% BPM groups (50.8 ± 2.1 and 48.5 ± 2.2%, respectively) (P ≤ 0.05). The nitrogen and energy budgets showed that increased dietary BPM levels reduced the branchial and/or renal nitrogen and energy losses and the energy spent on activity and maintenance, when calculated per kg gain. In conclusion, the present study shows that this quality of bacterial protein meal performs well as an alternative protein source to fish meal in feed formulation for the Atlantic salmon.