Microalga Phaeodactylum tricornutum in feed for Atlantic salmon (Salmo salar) —Effect on nutrient digestibility, growth and utilization of feed

• The potential of whole cell microalgae Phaeodactylum tricornutum was investigated as a feed ingredient for Atlantic salmon.
• Increasing dietary levels of algae from 0-12% gave a linear reduction in digestibility of dry matter, lipid, and protein.
• Algae can replace up to 6 % of the fishmeal without adverse effects on digestibility, FCR and growth of Atlantic salmon.

The aim of the present research was to investigate the potential use of the phototrophic microalgae Phaeodactylum tricornutum (P. tricornutum) as a fish meal replacement in diet for Atlantic salmon, Salmo salar. Two experiments were designed with fish meal based control diets and dried whole cells P.tricornutum replacing fishmeal in the ratios 3%, 6% and 12% (experiment one) and 3 and 6% (experiment two). Experiment one was a digestibility study lasting for 21 days, investigating effects of inclining level of P. tricornutum on apparent digestibility (ADC) of nutrients and energy. Experiment two was investigating ADC's of nutrients and energy, growth performance and nutrient retention in salmon fed for 82 days. The results from experiment one showed a linear reduction in ADC of dry matter (DM; P = 0.02), lipid (P < 0.0001), and protein (P = 0.04) with increasing level of algae biomass in the diet. The ADC of starch increased (P < 0.05) with algae inclusion level in both experiments. For experiment two, no effects were observed on digestibility of DM, lipid, protein, energy or ash, with 3 and 6% algae replacing fish meal. Neither was growth or feed conversion affected by 3 and 6% algae replacing fish meal. Increasing inclusion level of algae biomass caused an increase in whole body lipid. The ADC of saturated fatty acids was higher in fish fed 3% alga biomass compared to the 6% group. There was no difference in ADC or retention of n-3 fatty acids. In conclusion, the two experiments showed that P. tricornutum can replace up to 6% of the fish meal without adverse effects on nutrient digestibility, utilization of the feed and growth performance.Statement of relevanceMicroalgae are potential omega-3-contributing feed ingredients