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United States Department of Agriculture

Agricultural Research Service

Research Project: The Effect of Feed Ingredients and Feeding Regimen on Fecal Output of Rainbow Trout and Impact of Soy Products in a Serial Reuse System
2013 Annual Report


1a.Objectives (from AD-416):
1)Identify the effect of various soy products and animal by-products on fecal particle size. 2) Determine if diet digestibility affects fecal particle size. 3) Determine if the effect of feeding regimen, twice a day by hand to satiation versus simulated demand feeding the same amount over 12 hours, on fecal particle size distribution. 4) Compare the fecal particle size distribution of trout fed improved plant-based diets to commercial feeds. 5) How replacement of fish meal with different soy protein sources in rainbow trout diets affects water quality and fish health, including overall water turbidity, nitrogen (ammonia), and phosphorous production in a serial reuse raceway production system. 6) Determine the interaction of stocking density and diets with soy protein sources to affect growth, stress, and water quality. Evaluate these same diets while analyzing their affect on water quality including overall water turbidity and nitrogen and phosphorous production in a serial reuse raceway production system.


1b.Approach (from AD-416):
Aquaculture, as in all animal agriculture, has the task of effectively removing fecal waste from the rearing environment. In water, however, the task is more difficult since many factors can affect the consistency and size of feces. Several studies and commercial trials have demonstrated that feces from fish fed plant-based diets are more diffuse and difficult to remove than feces from fish fed a standard fish-meal diet. Two aspects will be considered in this project, with the first examining the effect of diet on fecal production and the second focusing on water quality and stocking density. Aspect 1: Dietary factors causing either diffuse or large feces have not been definitively determined, but the smaller the fecal particles the more difficult to remove by filtration or sedimentation. It is known that the diet digestibility affects total fecal production, yet it is unknown how the digestibility of various soy products affects fecal size. This project consists of 4 trials focusing on dietary and management factors affecting fecal particle size, and distribution of nitrogen and phosphorus, with the goal to develop improved plant based diets. Physiological parameters and gene expression will be monitored. In the first trial, eight soy products including standard and improved meals, feed grade soy protein concentrates from various sources and food grade SPC will be evaluated for fecal size and diet digestibility. The second trial evaluates the effect of feeding plant based diets with small amounts of animal by-products, algae, guar gum, and other ingredients thought to increase fecal size. The third trial determines the effect of feeding regime on fecal size. The next study will compare fecal size of trout fed improved plant based diets to commercial trout feeds. Incorporation of plant protein sources into trout feeds can increase water-borne phosphorous and ammonia in effluent and negatively affect receiving waters. Aspect 2: The impact of plant proteins on water quality could be minimized through improved diet formulation, including incorporation of novel soy protein products and processing. Furthermore, little information is available on how density of fish fed these diets affects water quality. Baseline information is needed on water quality of rainbow trout fed diets incorporating soybean meal and soy protein products. We currently have a research tank system that is uniquely equipped to study dietary effects on water quality. The system is capable of receiving 1st, 3rd, and 5th use water from a serial-reuse trout production hatchery and is able to monitor the water quality entering and exiting the system. To our knowledge, this is the only system of its kind available for monitoring multiple-use water in a trout production hatchery.


3.Progress Report:

Plant-based feeds for trout have been developed as part of the parent project, but it is very apparent these diets cause diarrhea in trout and salmon. This condition makes it difficult to remove the feces from the rearing water making compliance with discharge regulations difficult. The goal of the present project is to determine which ingredients cause the diarrhea and develop methods to prevent it, making plan-based feeds more acceptable to the producer and regulatory agencies. This project is just starting, but trials have been initiated both in Hagerman Idaho, and in Bozeman, Montana. In Idaho, the system that receives water of different qualities is up and operational and a feeding study has begun to determine if diet type affects the ability of fish to tolerate different qualities of water. In Montana, the system that collects fish waste from individual tanks is running and feces are being collected. Ten different diets are being fed that vary in the type of primary protein ingredient. It is thought that some protein cause diarrhea which reduces the effectiveness of solids reclamation. Three other studies are scheduled for this year focusing on finding solutions to waste manipulation through diet formulation.


Last Modified: 10/21/2014
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