Bacterial protein grown on natural gas as protein source in diets for Atlantic salmon, Salmo salar, in saltwater

Bacterial protein meal (BPM) produced on natural gas was evaluated with respect to growth, nutrient digestibilities, feed conversion ratios, sensory quality, and histopathological indices in Atlantic salmon in saltwater. In the extruded diets, experimentally produced BPM accounted for 0, 10, or 20% of the ingredients or 0, 17.2, or 33.1% of dietary nitrogen, replacing high-quality fish meal. Each diet was fed to two groups of salmon with a mean initial weight of 1.4 kg for 5 months. The pens were organized in two randomized blocks. One block was located with one side of the pens exposed to the open sea. The other block was completely surrounded by other pens. During the experiment, the salmon increased to approximately 3.6-3.9 kg in weight. Analysis of variance revealed no significant (P>0.05) differences in growth, but regression analysis showed that fish weights at 2 and 5 months and growth rates for the whole experiment were slightly reduced with increasing content of BPM. No significant effects of diet were seen on dressed-out carcass, liver, or intestine to body weight percentages. Carcass and visceral fat and dry matter contents decreased with increasing dietary BPM. There was a trend (0.10≤P<0.05) that apparent digestibilities of nitrogen, fat, and energy were reduced when substituting fish meal with BPM, while the nitrogen retention was not significantly affected. Flesh carotenoid concentration and colour were not significantly affected by dietary composition, nor were any differences seen for sensory characteristics related to taste, smell or texture. Histological examination did not reveal abnormalities, or signs of allergic reaction against BPM components, and hematocrit values were within normal ranges. Significant block effects were seen for chemical composition of viscera, and digestibilities of nitrogen, fat, and energy.