Abstract
Replacement of fishmeal (FM) with alternative plant proteins, especially soybean meal (SBM), can cause a diarrhea-like symptom in rainbow trout (RBT), characterized by very fine fecal particles. These fines do not settle out in raceway effluent for collection and can contribute to pollution of receiving waters. In this study, two experiments were conducted. Experiment 1 examined effects of nine protein sources (sardine meal, menhaden meal, soy protein concentrates (SPC) (three types), SBM (regular and high protein), corn protein concentrate (CPC), and poultry by-product meal (PBM)) on fecal particle size distribution. Results showed that all five soy-based diets produced feces in RBT having 75.7–89.3% fines and only about 1.0% large particles, while the remaining four diets yielded feces having a balanced particle size distribution. Oligosaccharides present naturally in soy products, thought to contribute fecal fines, were not correlated to fecal particle size classes. Instead, high crude fiber content in soy-based diets was found to be responsible for unbalanced fecal particle distribution in RBT. Experiment 2 examined if improvements in formulation could reduce the negative effect of soy-based ingredients. Eight practical diets (FM, SPC, SPC + 0.3% guar gum, PBM + CPC, PBM + CPC + 20 or 30% SPC, and PBM + CPC + 20 or 30% SPC + 0.3% guar gum) were formulated to contain 40% protein and 20% lipid. Results showed that diets containing mixtures of PBM, CPC, and 20% or 30% SPC plus guar gum produced trout feces with the highest percentage of large particles and lowest of fines, while the diet containing SPC alone (56%) plus guar gum resulted in trout feces having the highest content of mid-size particles. It was concluded that crude fiber in soy protein products (SBM and SPC) caused undesirable fecal particle profiles in RBT, and the addition of guar gum could significantly alleviate this negative effect.
Highlights
Fishmeal (FM) is the gold standard protein source for numerous fish species, including salmonids, due to its complete essential amino acid profile, high protein content, high digestibility, fatty acid profile, and palatability [1]
Experiment 1 was conducted to determine the effect of specific protein sources on fecal particle size (FPS) distribution, while Experiment 2 evaluated the effect of practical diets containing ingredients known to cause or prevent diarrhea and determine if improved formulation can decrease the diarrheic effect of soy protein concentrates (SPC) inclusion
Three types of SPC) were used as the primary protein source, the level of large fecal particles was significantly lower, but the level of fine fecal particles increased significantly compared with diets containing FM
Summary
Fishmeal (FM) is the gold standard protein source for numerous fish species, including salmonids, due to its complete essential amino acid profile, high protein content, high digestibility, fatty acid profile, and palatability [1]. As a strategy to reduce the risk, development of alternatives to fishmeal in aquaculture diets remains a high priority. Several animal proteins, including poultry byproduct meal (PBM), feather meal, blood meal, and others, have been utilized as a partial replacement of FM. They suffer from various downsides, such as low palatability, reduced digestibility, or inferior protein quality [1,3]. Oilseeds, grains, and their processing co-products are important aquafeed ingredients due to their abundance. Soybean meal (SBM) is the number one alternative source of proteins in aquaculture [4,5]
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