Nanoplastics (NPs) are emerging aquatic pollutants that may threaten farmed fish health. This study evaluated whether dietary nanocurcumin (NCUR) modulates NP-associated biological disturbances in largemouth bass (Micropterus salmoides). A total of 480 fish (initial weight 11.52 ± 0.02 g) were assigned to four treatments for 21 days: control, 0.2% NCUR, 100 μg/L NPs, and 0.2% NCUR + 100 μg/L NPs. NP exposure significantly reduced growth and feed intake (p < 0.05) and was accompanied by gill, hepatic and intestinal tissue alterations, disturbed serum lipid parameters, changes in hepatic antioxidant enzyme activities, and altered mRNA expression of antioxidant- and metabolism-related genes. Dietary NCUR was associated with partial modulation of several NP-associated responses, including hepatic and intestinal structural alterations, serum lipid changes, adaptive antioxidant enzyme responses, and transcriptional changes in Nrf2/Keap1- and SIRT1/FoxO1-associated genes. However, NCUR did not alleviate NPs-induced gill damage, and NCUR alone also caused branchial histopathological alterations. Therefore, 0.2% NCUR may partially mitigate selected NPs-induced disturbances in M. salmoides, but its independent effects, branchial safety, and pathway-level mechanisms require further investigation.