Assessment of the nutritional and effluent properties of potential fish-meal-free diets for rainbow trout (Oncorhynchus mykiss W.) in Iran

Abstract

Research is needed on alternative ingredients for aquafeeds due to rising demand and limited fish meal availability. This study evaluated fish-meal–free diets for rainbow trout in two phases. The first phase focused on assessing the growth performance and nutrient digestibility of six cold-pelleted diets. Aside from the control diet, the test diets contained poultry protein concentrate, blood meal, low-ash poultry by-product meal, 20–40% canola meal, and feather meal (Goldmehl^®). Juvenile fish, averaging 5.3 g, were fed the diets for 56 days in a random-block design with four replicates per feed. Feces were collected using the settling method to evaluate nutritional digestibility and phosphorus availability. The feed from the primary phase, which resulted in the least-cost feed conversion ratio, was extruded and fed to fingerlings (14.6 g) in the second phase. This trial added to the first run in measuring digestibility parameters over a 28-day period. In parallel, extruded feed was given to grow-out fish, averaging 172.5 g, for 55 days in triplicate completely randomized tanks to evaluate growth performance and nutrient effluents. Throughout all the experimental runs, a casein-based laboratory pelleted feed was used for the respective controls. Feeding rainbow trout with 35% canola meal in both pelleted and extruded forms showed comparable results (P > 0.05) to the control in terms of growth performance and apparent digestibility for lipid (> 91%), crude protein (> 87%), and organic matter (> 78%). The extruded feed in this study represents an eco-friendly option for the growing aquafeed sector.