Changes of phosphorus absorption from several feed ingredients in rainbow trout [Oncorhynchus mykiss] during growing stages and effect of extrusion of soybean meal

The absorption of phosphorus (P) contained in several feed ingredients by rainbow trout was compared during the growing stages of the fish. The ingredients tested were pollock meal, sardine meal, poultry feather meal (PFM), meat and bone meal (MBM), defatted soybean meal (SBM), soy protein concentrate (SPC), corn gluten meal (CGM), and defatted soybean meal extruded at 150degC (exSBM). Phosphorus absorption was determined for fish of sizes 2g, 5g, 10g, 20g, 50g, 100g, and 200g. Absorption of P from the two fishmeals slightly decreased as bodyweight increased. Conversely, P absorption from PFM and the plant ingredients was very low by the 2g fish, but increased during the early growth stages and seemed to have reached a plateau in fish bigger than 10g. Absorption from exSBM was much higher than that from SBM at all bodyweights examined. Phosphorus absorption from the different ingredients were: pollock meal 31-46%; sardine meal 49-59%; MBM 36-46%; PFM 36-84%; SBM 3.4-37%; exSBM 25-58%; SPC 3.7-34%; and CGM, 0-17%. The results demonstrate that, depending on the ingredient P absorption in rainbow trout changes as the fish grows. Extrusion cooking at 150degC improved the availability of P in SBM.