| Sumario: | In order to become a more profitable and sustainable industry, the aquaculture sector is constantly exploring
alternative nutrient sources. In the present study, the natural stable isotope signatures of different animal-, plantand microbial-derived ingredients were determined to evaluate the assimilation of dietary nitrogen in Pacific
white shrimp. Experimental diets were manufactured to replace fish meal and squid meal with microbial- and
plant- derived ingredients (48 and 66 % dietary inclusion) and were also used as additives (4%). Ingredients
were also used as additives to study their effects on growth performance and assimilation. Corn gluten, soy
protein isolate, Arthrospira (Spirulina) biomass and a bacterial meal (ProFloc™) were used to formulate six,
isotopic control diets containing one source of dietary nitrogen, while six combined diets had varying proportions
of ingredients. At the end of the trial, survival rates were similar among treatments (88 ± 9%) but there
were significant differences in mean final weight. Microbial and animal proteins promoted similar final weight
when combined (1080−1537 mg), while plant ingredients and Arthrospira caused lower growth when used
alone (420−970 mg). Isotopic values indicated significant differences in the assimilation proportions of dietary
nitrogen, mainly attributed to the ingredients’ different amino acid profiles. The dietary nitrogen contained in
microbial-derived ingredients was assimilated at similar, or even higher proportions than fish meal and squid
meal. Diet formulated with 33 % fish meal, Arthrospira and corn gluten, contributed 31, 36 and 33 % of dietary
nitrogen to muscle growth, respectively. The second 33 % combination supplied 42, 34 and 24 % from squid
meal, bacterial meal and soy protein. When ingredients were used at 4%, additive levels, they also contributed
structural nitrogen to shrimp muscle tissue despite low dietary inclusions. Results demonstrated the viable use of stable isotopes to evaluate the assimilation of dietary nitrogen supplied by emerging alternative ingredients
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