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Not AvailableAn eight-week feeding trial was conducted to investigate the effect of dietary krill meal inclusion in diets with moderate (12pert) and low (6pert) fishmeal concentrations for Penaeus vannamei. Inasmuch, eight iso‑nitrogenous and isolipidic diets were formulated to contain 36pert crude protein and 5.5pert crude lipid. In the moderate-fishmeal diets, krill meal was included at 0, 2, 4 and 6pert (called FK12:0, FK12:2, FK12:4 and FK12:6, respectively), likewise in the low-fishmeal diets, krill meal was included at the same concentrations of 0–6pert (called FK6:0, FK6:2, FK6:4 and FK6:6, respectively). Shrimp with a starting body weight of 0.55 ± 0.02 g were stocked at 22 animals per tank of 350 l capacity and fed three times daily. Results revealed that dietary krill meal and fish meal inclusion levels significantly increased growth performance (P 0.05). Survival was significantly increased in the groups containing 6 and 4pert krill meal diets compared to 0pert krill meal diet (P < 0.05). Inclusion levels of krill meal showed non-significant differences in post-fed body composition except for crude lipid and crude fibre content. Fishmeal inclusion levels showed significant (P < 0.05) variation in C14:0, C16:0, C18:0, C16:1,C18:1n-9, C18:2n-6, C22:6n-3, n-3/n-6 ratio, whereas krill meal inclusion levels showed significant variation in the all n-3 fatty acids only. Immune-related gene expression was significantly (P < 0.05) upregulated in the shrimp fed high fishmeal diets (12pert) for all the analyzed genes ProPhenoloxidase (ProPO), ProPhenoloxidase activating enzyme (PPAE), Serine Protease (SP), β-1, 3-glucan-binding protein (BGBP), Superoxide dismutase (SOD), and Hemocyanin (HC). The dietary change led to a significant difference in both histology and haematology parameters (P < 0.05). The results inferred that krill meal could be used as a potential functional feed ingredient in Penaeus vannamei.The present study suggested beneficial effects of krill meal in shrimp diets. The levels of fishmeal inclusion (12 and 6pert) also showed significant (P < 0.05) variations in various growth performance parameters. It is plausible that an inclusion level of 4pert is the minimum for a measurable difference in growth performance.Not Availabl