Abstract
Commercial aquafeed diets currently contain marine fishmeal (FM) as a major ingredient. FM is included due to its rich nutrient profile and palatability, helping to meet the nutritional requirements of fish. Due to the rapid growth of aquaculture and lack of abundance of FM, there is an increasing strain on the use of FM in aquafeed. To keep meeting aquaculture production demands, alternative protein sources, such as soybean meal (SBM), must be utilized in aquafeed diets to reduce the FM inclusion. SBM is one of the most common plant-based ingredients to replace FM in aquafeed diets due to its relatively high protein and essential amino acid (EAA) content, with the exception of lysine and methionine. SBM, although advantageous in approaching the nutritional requirement of various species, comes with some limitations. High SBM inclusion in carnivorous aquafeed diets for species such as Rainbow trout or Atlantic salmon (Salmo salar) have been determined to cause soybean meal-induced enteritis (SBMIE). SBMIE is the inflammation of the distal intestine caused by the inclusion of SBM in feed. The overall goal of this study was to discover how much SBM inclusion can be utilized by Atlantic salmon throughout different life stages. Five experimental diets containing increasing levels (0, 10, 20, 30, and 40%), of SBM were formulated and manufactured to meet the nutritional needs of Atlantic salmon. The salmon, initially weighing ~ 10.0 ± 0.5 g, were randomly distributed into 15 60-L tanks (35 fish/tank) at the Aquaculture Research Institute, University of Idaho. During the 22-week trial, fish were sampled three times (weeks 8, 12, and 22) to measure the growth performance and distal intestinal histology and gene expression. Increasing SBM inclusion in the diet enhances gut inflammation in salmon. However, it was additionally revealed that SBM inclusion levels above 20% negatively affects the antioxidant capacity of the fish and make the fish more vulnerable to oxidative stress, as significant differences were found in the expression of cat and sod genes in the liver, specifically in SBM levels above 20%. In total, the outcome of this project supports 20% SBM inclusion in Atlantic salmonid aquafeeds.