<p>Copper is an essential trace element for fish, yet defining its optimal dietary levels remains a challenge in aquaculture nutrition. This meta-analysis quantitatively evaluated the effects of dietary copper supplementation on fish growth performance, superoxide dismutase activity, tissue copper levels, and body composition. Significant benefits in terms of fish survival, weight gain, hepatic Cu–Zn superoxide dismutase activity, and copper concentrations in the whole body, liver, and intestine were observed following supplementation with varying levels of copper, while excessive copper intake (&gt; 25 mg/Kg) led to trade-offs in feed conversion, protein efficiency, and condition factor. Meta-regression identified that dietary copper levels, source of copper, feeding duration, and main protein content in the diet significantly moderated effect sizes of weight gain. Piecewise regression showed that the optimal dietary copper concentration determined to be 5.7 mg/kg. Structural equation models revealed that increased dietary protein and feeding duration enhance effect sizes of weight gain through elevated copper and crude protein levels in the body. This study provides a nuanced understanding of dietary copper supplementation effects on fish physiology, offering valuable insights for formulating diets that enhance aquaculture productivity while maintaining fish health.</p>