The study investigated the effectiveness of three extruded feeds in the feed conversion index for the rainbow trout (Oncorhynchus mykiss Walbaum, 1792) reared at the Ain Aghbal fish farming station in Morocco. While the biochemical composition (moisture, protein, lipid, and carbohydrate percentages) and energy content (digestible and raw) of feeds A, B, and C are known, these factors alone are insufficient for selecting the optimal feed based on conversion index. The test was conducted over 222 days in tanks supplied with water from Oum Er-Rbia, flowing at 11.04m³/ h, with a water change every half an hour. Initial rearing conditions included a density of 1.58kg/ m³ and a volume-to-flow ratio of 1.05m³/ h. Fish were fed two to three times daily, depending on their growth stage. Results indicate that extruded feed B significantly improved the rainbow trout growth and achieved a conversion index not exceeding 0.9 for the trout weighing 1043g.