The study consisted of two separate nursery trials in which post-larval (PL) L. vannamei were fed graded dietary levels of astaxanthin krill oil (QRILL™ AstaOmega Oil, Aker Biomarine Antarctic AS, Norway). In the first trial (trial #01), 142,245 PLs of 3.6 ± 0.3 mg body weight (BW) were stocked under 2.4 PLs/L (3,556 ± 31 PLs/tank) in forty 1-m3 outdoor tanks and raised for 51 days. Shrimp were fed 20 times day and night with diets containing 0 (AKO0), 1.00 (AKO1), 3.00 (AKO3), and 5.00% (AKO5) astaxanthin krill oil (AKO) included at the cost of soybean oil (SBO) and soy lecithin oil (SLO). Diets were formulated to contain 18.00% salmon meal, along with 4.45% of poultry viscera and bone meal, 20.39% soybean meal (SBM), 10.00% wheat gluten meal (WGM), and 8.00% soy protein concentrate (SPC). After harvest, a stress test was carried out to evaluate shrimp resistance to a sudden and acute change to water salinity and temperature. In trial #02, 65,588 PLs of 2.5 ± 0.3 mg BW (1,252 ± 29 PLs/tank) were raised in fifty 0.5-m3 indoor tanks for 42 days. Shrimp were fed 8 times a day exclusively in feeding trays. A negative control (AKO0KM0) diet was formulated without any AKO. It contained 29.80% salmon meal combined with 18.98% SBM, 7.00% SPC and 5.00% WGM. Four other diets were prepared by partly replacing salmon meal for 8.00% of a high-protein krill meal (KM, QRILL™ Aqua High Protein, Aker Biomarine Antarctic AS, Norway), including a positive control (AKO0KM8) without AKO. Other diets were formulated with 3.00 (AKO3KM8), 5.00, and 7.00% AKO added at the cost of SLO and SBO. In trial #01, no statistical effect from the inclusion of AKO was observed on final shrimp survival (84.0 ± 16.8%), gained yield (1,568 ± 181 g/m3), daily growth (14.2 ± 2.8 mg/day), apparent feed intake (AFI, 1.12 ± 0.07 g of feed/shrimp) and feed conversion ratio (FCR, 1.70 ± 0.16). However, shrimp fed KO5 achieved a statistically higher final BW (857 ± 140 mg) in comparison to all other diets. In trial #02, shrimp final survival (91.8 ± 14.2%), gained yield (1,611 ± 181 g/m3), daily growth (14.2 ± 1.8 g/m3) and FCR (0.89 ± 0.09) were not significantly affected by dietary treatment. There was significant effect of AKO over AFI, starting at 3% dietary inclusion. Shrimp fed diets containing AKO significantly enhanced final BW starting at 3% dietary inclusion (AKO3KM8, 629 ± 76 mg), but not beyond this level. Shrimp fed diets with 5 and 7% AKO (613 ± 81 and 612 ± 105 mg, respectively) did not improve BW compared to 3% or to the diet with KM only (KO0KM8, 583 ± 55 mg). There was no positive effect over shrimp final BW as a result of the inclusion of 8% KM since it did not differ from shrimp fed the control diet (AKO0KM0, 567 ± 65 mg). In the stress test, when water salinity dropped from 39 g/L to 0, shrimp survival showed a clear trend towards higher survival due to the progressive increase in the dietary inclusion of AKO. A minimum of 1% AKO (AKO1, 80.0 ± 10.00%) was sufficient to promote an enhanced survival compared to 0% AKO (66.7 ± 15.28%). However, at 5% (AKO5), no shrimp mortality was recorded after 30 min. of exposure. Also, a drop in water temperature from 27.9 to 19.2 ± 0.9oC resulted in a statistically higher survival in shrimp that had been fed a minimum of 3% AKO (91.7 ± 5.16%) compared to without (AKO, 66.77 ± 10.33%) after 30 min. of exposure. This study has shown that post-larval L. vannamei fed nursery diets containing 5% AKO or 3% AKO in combination with 8% KM achieves a significantly higher BW at harvest. A minimum of 3% AKO is required to promote a greater resistance to an acute osmotic and thermal stress.