This study aimed to evaluate the efficiency of Wolffia (watermeal) supplementation on the growth performance of guppy fish (Poecilia reticulata). Wolffia was added to the commercial fish diet at proportions of 15%, 30%, 45%, and 60%. Nutritional analysis revealed that 100 grams of Wolffia contained 22.16 grams of protein, 49.2 grams of carbohydrates, 3.78 grams of fat, and provided 319.46 kilocalories of energy. All groups of fish showed weight gain throughout the experiment, with significant differences observed from week 5 (p<0.05). At week 6, the group receiving 60% Wolffia had the highest average weight (0.66±0.09 g), followed by the 45% group (0.64±0.11 g). Both groups had significantly higher weights than the control (0.50±0.14 g) and the 15% and 30% groups. The average body length also increased with higher Wolffia supplementation, with the 60% group reaching the greatest length (3.78±0.11 cm). However, the 45% group demonstrated the best growth efficiency, with the highest average daily growth rate (0.00429 g/day) and specific growth rate (0.79%/day). Feed conversion ratios in the 45% and 60% groups were the best at 0.18. The highest survival rate (97.07%) was recorded in the control and the 15% and 30% groups, while the 45% and 60% groups showed 88.46%, with no significant difference (P = 0.058). Therefore, the study concludes that a 45% Wolffia supplementation is the most suitable level for enhancing guppy growth performance Keywords: Wolffia, watermeal, guppy, plant protein, growth performance