An Evaluation of Nitrogen Supplementation and Processed Soy Fractions on the Performance of Cultured Fishes

World population growth has resulted in an increased demand for a sustainable food supply. This rapid growth coupled with an increased per capita consumption of seafood, has resulted in many of the world’s marine fisheries being over-exploited in an effort to meet the global demand for seafood. Aquaculture has attempted to fill the supply and demand gap created by the dwindling supply of fish in the world’s oceans. Fishmeal (FM) has traditionally been the primary protein ingredient in aquafeeds fed to farm-raised fish, however its unstable supply and increasing price have driven researchers to identify alternative protein sources. Soybean meal offers a viable alternative with a stable supply at a low price. This research focused on how nitrogen inclusions and varying processing treatments may improve nutritional characteristics of soybean meal for use in aquafeeds. Bioprocessing combined with nitrogen supplementation has the potential to reduce antinutritional factors (ANFs) such as trypsin inhibitors, antigens, saponins, lectins, oligosaccharides, and phytate while simultaneously increasing protein levels. The first two feeding trials were completed to determine a palatable source and concentration of nitrogen for potential inclusion during bioconversion to limit the risk of nutrient limitation of Aureobasidium pullulans. In the first palatability study, three nitrogen sources, ammonium chloride, diammonium phosphate, and urea, were included (1,250 ppm) into diets of rainbow trout (Oncorhynchus mykiss) containing a bioprocessed soybean meal (BP-SBM) in place of fish meal (FM) and feed consumption was monitored. No significant differences in consumption occurred, however it was noted that the diet containing urea was consumed slightly more than the other two nitrogen supplemented diets. Therefore, in a follow-up palatability study urea was supplemented at varying inclusion levels (0, 500, 1,000, 1,500, and 2,000 ppm) to rainbow trout diets containing BP-SBM in place of FM. The study revealed nonsignificant palatability responses when consumption and growth parameters were analyzed among treatments. The results indicate that up to 2,000 ppm urea can be potentially supplemented to Aureobasidium pullulans during bioprocessing without any adverse effect on palatability of rainbow trout feeds. In further examining bioprocessing as a feasible approach to enhancing soy, six experimental soy ingredients were processed and formulated into aquafeeds and fed to rainbow trout and hybrid striped bass (Morone saxatilis x M. chrysops) in separate feeding trials. The performance of these experimental ingredients was tested against a FM control through digestibility and growth trials (105-day). The optimal experimental soy ingredient in each trial was determined based on consumption, growth, feed efficiency, apparent digestibility, and health indices. The experimental ingredient with the highest apparent digestion coefficient of protein (ADC-P) when fed to hybrid striped bass was the BP-SBM ingredient with an enzyme inclusion (Diet 4). This ingredient was found to have a significantly higher ADC-P than the soybean meal negative control ingredient (SBM). Growth trial experiments revealed that Diets 1 and 2 (BP-SBM fraction #1 and BP-SBM fraction #2) were the top performing diets fed to rainbow trout when comparing growth parameters and health indices. Diets 1 and 5 (BP-SBM fraction #1 and the washed base BP-SBM ingredient) were the top performing HSB diets when comparing growth parameters and health indices