Feeds and Feeding Methods for Larval and Fingerling Walleye

The Iowa DNR Rathbun hatchery produces 170,000 advanced walleye Sander vitreus (225-250 mm) in five months using a three-phase culture regimen with measured growth rates of 1.5 mm/d and survival of 72% from fry to 225 mm. The success of this production process requires feeds and feeding regimes that optimize growth and survival. Fingerlings reared from fry in fertilized lined ponds are transferred to indoor tanks and fed an imported conversion diet with 58% protein and 15% fat with crumble particle size range of 920 to 1410 µm. Fish are fed 8 to 10% bodyweight/d at 5 minute intervals, 22 h/d during habituation. After ten days fish are transitioned to an extruded 1-mm Walleye Grower 9206 (WG 9206) pellet with 52% protein and 17% fat. Feed frequency is reduced to 10 minute intervals after 17 days. Feed size is increased gradually, reaching a 4 mm extruded pellet at 180 mm fish length. Feed rates during growout are calculated based on measured growth rate (mm/d) and biomass gain; feed rates decline to 2% by harvest in October. Experimentally, but not on a production basis, 3 day old fry are cultured intensively in tanks using turbid water. Fry are fed an imported microparticulate larval feed with 54% protein and 16% fat at an initial rate of 4 g/1,000 fry/d. The larval feed size starts with 200-360 µm and is progressively increased until the fish are ready for transition to 1.0-mm WG 9206. The intensive larval culture system produced good growth and high survival rates (e.g., 75% in 2010), but deformities of several types have been common and prevent fingerling use in fisheries enhancements. While manufacturing technology exists to produce high quality microparticulate open-formula feeds in the United States, the lack of knowledge of digestive function and nutritional requirements of fry limit our ability to formulate feeds that reduce deformity and have acceptable growth rates.