This study evaluated the inclusion of krill-meal and soy protein concentrate (SPC) in microdiets for whiteleg shrimp post-larvae (PL). Four experimental diets were tested: BASE (marine and plant proteins), KRILL (krill-meal as main protein), NKRILL (no krill-meal), and NSOY (no SPC), alongside two commercial diets (ComA and ComB). After 21 days, growth and survival data showed that most experimental diets outperformed one or both commercial options. SPC can partially replace marine proteins without negatively affecting growth or survival. However, completely removing krill-meal impaired PL health, indicating benefits to its moderate inclusion. Under acute ammonia stress, survival rates were similar across all diets. Still, PL fed NKRILL and the commercial diets showed higher activity levels of antioxidant molecules, possibly due to lower dietary antioxidant input and compensatory endogenous production. Following a Vibrio harveyi challenge, PL fed the BASE diet had higher survival than those fed NKRILL, NSOY, and ComB, reinforcing that krill-meal exclusion (NKRILL) negatively affected health. Additionally, removing SPC (NSOY) seemingly reduced PL resistance to infection. Conversely, the gene expression analysis suggested an apparent compromised health status in PL fed NSOY, which matched the lower survival values compared to BASE. In summary, SPC can successfully partially replace marine proteins without compromising PL growth performances and survival, while krill-meal appears important for maintaining PL health and immune function.