Soybean meal (SBM) is one of the most commonly used alternative plant-based ingredient to replace marine derived fish meal (FM) in aquafeed. Relatively high protein content and favorable amino acid profile of SBM approaches the nutritional requirement of many cultured species. However, dietary utilization of SBM in carnivorous fish feeds has been limited by the presence of several anti-nutritional factors (ANFs) that may affect the digestion or absorption of nutrients, resulting in decreased growth performance and feed efficiency in finfish. When Atlantic salmon is fed on SBM-based diets, the morphology of the distal intestine is disturbed in terms of ‘non-infectious sub-acute enteritis’. The changes in the distal intestinal mucosa are described as a deep shortening of the mucosal folds (MF), a decreasing number of supranuclear vacuoles (SNV) in absorptive cells, a widening of the central stroma with a correspondingly high amount of connective tissue and an increased infiltration of inflammatory cells in the lamina propria (LP), an increased number of goblet cells (GC), and a shortening of the microvilli (Mv).
The overall aim of this study was to increase the usage of SBM in feeds for Atlantic salmon. The specific objectives of this study were to optimize the dietary SBM inclusion level in Atlantic salmon at different life stages. Five experimental diets were formulated. Diet 1: FM based diets (30% FM and 0% SBM); Diet 2: 10% SBM, Diet 3: 20% SBM; Diet 4: 30% SBM and Diet 5: 40% SBM. Diets 2 – 5 contains 10% FM along with SBM. A total of 525 fish (juvenile) were stocked in triplicates in 15 tanks of recirculating aquaculture system. The fish were fed by hand to apparent satiation two times per day, six days per week for 22 weeks. Feed intake was measured every day. Fish were weighed and sampled (distal intestine and liver) on 4th, 8th, 12th and 22nd week.
The results showed growth performance, feed intake and feed utilization parameters were significantly affected by dietary treatments. Feed conversion ratio was significantly highest in 10% SBM diet fed group up to 8 weeks whereas growth rate was highest in 40% SBM fed group. Growth performance and feed utilization data were measured for 22 weeks. Results for gut histology and immune related genes will be presented.