Straw mushroom (Volvariella sp.) myco-meal replaced up to 50% of soybean meal in whiteleg shrimp (Litopenaeus vannamei) feed without hurting growth or survival. The 50% replacement group had the strongest growth response, with 4518% weight gain, 8.52% specific growth rate, and 87.5% feed conversion efficiency over 60 days. Higher levels raised immune-cell counts and gut lactic acid bacteria, but 75–100% replacement lowered blood glucose, making 50% the sweet spot for sustainable shrimp nutrition.