The present study investigated the effects of natural additives, ginger (Zingiber officinale) and garlic (Allium sativum), on growth performance, feed conversion ratio, and survival rate of juvenile rainbow trout (Oncorhynchus mykiss). Five diets containing 0% ginger and garlic (CON), 1% ginger (GN1), 1 % garlic (GR1), 2% ginger (GN2), and 2% garlic (GR2) were formulated and fed to 3600 rainbow trout (average weight: 3.52 ± 0.15 g) distributed to 15 raceway tanks. Final weight was significantly higher in GN1 than CON, GR1, and GR2 (p < 0.05), with weight gain similarly surpassing CON, GR1, and GR2 (p < 0.05). Final length was significantly greater in GN2 than GN1 and GN2 (p < 0.05). Specific growth rate in GN1 was significantly higher than CON, GR1, and GR2 (p < 0.05). Average daily weight gain was significantly higher in GN1 than CON and GR1 (p < 0.05). Similarly, condition factor was significantly higher in GN1 than CON, GR1, and GR2 (p < 0.05). Feed conversion ratio was also notably lower in GN1 than CON and GR1 (p < 0.05). Survival rate remained unaffected across all levels of dietary garlic or ginger inclusion (p > 0.05). These results provided insights into the roles of dietary ginger in promoting growth and feed conversion ratio in rainbow trout. Dietary ginger is therefore recommended for rainbow trout as a cost-effective and environmentally friendly feed supplementation.

Keywords: Herbal additives, medicinal plants, immunostimulant, trout, nutrition