Journal of Aquaculture & Marine Biology

Because of the paucity of studies evaluating commercial salmonid diets, the recent availability of new commercial feeds, and the large impact of such feeds on fish growth, mortality, and hatchery economics, additional studies are definitely warranted.Thus, the objective of this study was to compare the performance of an established feed and a recently introduced feed during the hatchery rearing of juvenile rainbow trout. Methods and materialsThis experiment occurred at McNenny State Fish Hatchery, rural Spearfish, South Dakota, USA using aerated well water at a constant temperature of 11 °C (total hardness as CaCO 3 , 360 mg/L; alkalinity as CaCO 3 , 210 mg/L; pH, 7.6; total dissolved solids, 390 mg/L).Four feed trials were conducted.Each trial focused on a specific feed size, with the first trial evaluating starter feeds, the second trial evaluating #1 granules, the third trial #2 granules, and the fourth trial 1.5 mm pellets. Trial 1Trail 1 began immediately after yolk sac absorption on 9 October 2024 and ended after 18 days of feeding on 28 October 2025.Thirty individual rainbow trout swim-up fry were weighed to the nearest 0.01 g, and measured (total length), to the nearest 0.01 mm.Approximately 7,900 (weight = 0.51 kg) trout were placed into each of the eight 190-L (160-L working volume) semi-square tanks.Feeding commenced the day after placement of the fish in the tanks.Flows were similar along all tanks.Feed amounts were figured using the hatchery constant method 14 , with an expected feed conversion ratio of 1.1.Growth rates were projected to be at, or slightly above, satiation and gradually increased as the fish became feed-trained.They were 0.04 cm/day for the first week of the trial, 0.05 cm/day for the second week, and 0.06 cm/day for the final four days of the trial.Feed amounts were also adjusted weekly based on the weight and total length of five fish per tank.Two commercially-available starter diets were used in the eight tanks.Four tanks of fish received BioVita starter #0 granules (Bio-Oregon, Longview, Washington, USA) and four tanks received Optimal #0 trout granules (Optimal Fish Food LLC, Omaha, Nebraska, USA).Table 1 is the ingredient list for each diet and Table