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United States Department of Agriculture

Agricultural Research Service

Research Project: Improving Sustainability of Rainbow Trout Production by Integrated Development of Improved Grains, Feeds, and Trout

Location: Small Grains and Potato Germplasm Research

2012 Annual Report

1a. Objectives (from AD-416):
The objective of this research is to improve the sustainability and production efficiency of rainbow trout by developing innovative feeds that reduce dependence on marine fishery resources. Objective 1: Identify and develop grain lines with desirable traits for either direct or indirect use in aquafeeds. Objective 2: Develop mechanical, chemical and biological methods to improve the nutritional and anti-nutritional profile of grains, by-products and other alternative ingredients. Objective 3: Determine nutritional value of alternative ingredients (protein, lipid, energy) and develop practical feed formulations for improved strains of fish. Objective 4: Determine optimal nutrient supplementation levels for specific life stages of improved strains of trout. Objective 5: Use gene expression analyses to advance the understanding of gene targets for improving nutrition, growth, and development processes under production conditions. Objective 6: Identify phenotypic differences in rainbow trout for growth and utilization of plant-based sustainable diets and determine the genetic variation for the identified traits.

1b. Approach (from AD-416):
A multidisciplinary approach will be used combining expertise in the fields of plant genetics, grain processing, fish nutrition and physiology, and fish genetics. Grain lines will be identified that have traits desirable for fish feeds. Phenotypic differences in trout for their ability to utilize plant-based feeds will also be identified. Grains will be further modified through physical, biological or chemical methods to improve their nutritional profile for trout. Feeds will be formulated using alternative ingredients to fish meal and to meet the nutritional requirements for improved strains of trout. This project will benefit; fish farmers through improved feeds and environmental compliance through reduced nutrient release, identified traits and markers to aid stock improvement efforts, feed manufacturers with alternate ingredients, reduced costs, price stability, and improved diet formulations, and grain farmers with new markets and products, and the consumer with a safe, sustainable, nutritious food supply and cleaner environment.

3. Progress Report:
Progress was made on Obj. 2-6, and Obj. 1 is not active due to critical personnel vacancy. Obj. 2; mechanical and chemical methods were developed to improve the nutrient content of 5 potential ingredients. Data from a feeding study demonstrated some of the ingredients to be high quality such as 2 novel co-products from ethanol production, but changes in processing were required for others. Of the almonds harvested in the U.S., 25% are considered low value waste with much of it sold as cattle feed. A method was developed in collaboration with an industry partner to remove fiber and other non-desirable components to produce a 55-60% protein meal. Obj. 3; trout fry screening studies were used to evaluate a variety of alternative ingredients and are designed to quickly determine (6 weeks) the effect of an ingredient on the palatability, digestibility, and ANF content of a diet. During two studies, 24 diets were each fed to 4 tanks of 100 trout. Results indicated strong potential for some ingredients produced in-house and commercially available. Using sub-adult rainbow trout, the nutrient digestibility of nine algae’s and 3 types of cottonseed meal was determined and data has been added to the projects on-line database. Obj. 4; the amount of phosphorus (P) in the effluent from trout farms is a primary factor limiting expansion of the trout industry. A study is underway to determine the optimal level of P with two sources, each at 4 levels, for trout fry with plant based feeds. Feeding studies were conducted to determine optimal levels of copper and zinc, and possible interactions, in plant based diets for trout. Supplementation levels were different in fish meal as compared to plant based diets. Research under sub-obj. 4b has been delayed due to facility installation at a commercial partner’s farm, and is expected to be operational by 8/1/12. Obj. 5; trout were fed diets of varying protein and lipid ratios, and compared to fish fed a standard 45% protein/15% lipid feed. Modeling of trout growth based on nutrient utilization was done with analysis of body composition, protein turnover and expression of genes related to major catabolic pathways. In another study an improved strain of trout when fed plant protein-based feed and a control strain of trout were fed either a fish meal diet or a plant protein diet. Liver, intestine, muscle samples were processed for the development of libraries in preparation for RAD labeled sequencing. Obj. 6; trout were fed diets varying in energy content and analyzed for changes in growth and other performance criteria. Selected and control strains of trout were also fed a standard diet and a plant-based diet for 3 months. At the end of the trial the intestinal tracts were removed from the 4 groups of fish and analyzed immunohistochemically. Another study was conducted to determine if genetic variation exists in rainbow trout for the ability to desaturate and elongate fatty acids by feeding diets with different fatty acid contents. Variation in different families was evaluated and fish tissues were isolated and analyzed for fatty acid content and expression of genes involved with lipid conversion and deposition.

4. Accomplishments
1. Method developed to recover high value co-products from the grain-based ethanol production. There is increasing production of fuel ethanol in the U.S. and the primary co-product is corn distiller's dried grains with solubles (DDGS). The quantity of this low value product is also increasing and is used primarily in limited amounts in cattle feeds due to an imbalance of nutrients. Scientists with the Small Grains and Potato Germplasm Research Unit in Aberdeen, Idaho developed a new processing method that will produce more consistent, higher protein DDG and two new products, a protein and a mineral source with improved nutrient profiles. Feeding trials with rainbow trout demonstrated that both products are highly digestible, which is vitally important to the trout industry. This new process can be easily added to the existing process and it 1) reclaims valuable phosphorus and protein from the soluble’s and 2) separates the nutrients into distinct products, thus increasing the overall flexibility, economic value, and sustainability of ethanol production.

2. New protein source for aquafeeds developed from almond processing waste. Approximately 2 billion pounds of almonds are produced in the U.S. each year and approximately 25% is considered waste in the form of broken pieces and fines and is fed to cattle. Scientists with the Small Grains and Potato Germplasm Research Unit in Aberdeen, Idaho, in collaboration with U.S. based Adaptive Bio-Resources LLC, developed a process to partition this waste into several new products for both the human food and aquafeed markets. Trout feeding studies have demonstrated high digestibility and palatability for the ~60% protein almond meal. Identifying and developing new sources of plant-based protein for aquafeeds will increase the profitability and sustainability of aquaculture production.

3. Trace mineral supplements in trout diets are dependent upon type of diet. The composition of aquaculture feeds is changing from fish meal based to include primarily plant derived ingredients. Scientists with the Small Grains and Potato Germplasm Research Unit in Aberdeen, Idaho, in collaboration with scientists with the U.S. Fish and Wildlife Service and Montana State University, conducted several studies investigating the effect and interaction of the type of diet and supplemented copper and zinc levels. These studies demonstrated an increased need for copper and zinc in plant based diets and provides the basis for the development of a trace mineral supplement formulated specifically for modern trout diets. Optimizing trace mineral additions to modern aquafeeds will ensure animal welfare, optimize growth, minimize feed costs, and reduce accumulation of trace minerals in fish waste.

4. Ability to reduce the use of fish oil in salmonids feeds. Feed is the highest variable cost in aquaculture production, with fish oil being one of the most expensive feed ingredients. Fish oil in trout feed is the primary source of the healthy omega-3 fatty acids EPA and DHA found in trout fillets. Scientists with the Small Grains and Potato Germplasm Research Unit in Aberdeen, Idaho evaluated the ability of several families of rainbow trout to convert plant oils to omega-3 fatty acids and store them in their tissues. The study clearly demonstrated that genetic variation exists between families for this ability. Rearing rainbow trout improved for this trait should reduce feed costs and the industry’s current dependence on fish oil, while sustaining the beneficial fatty acids currently found in trout fillets.

5. Improved digestive tolerance of rainbow trout selected to grow when fed plant-based feeds. Expensive fishmeal-based feed is the main production cost for trout growers. Scientists with the Small Grains and Potato Germplasm Research Unit in Aberdeen, Idaho have developed an improved strain of rainbow trout that grows faster and more efficiently when fed a fishmeal-free, plant-based diet. The improved fish have adapted parts of their intestinal tract to utilize a plant-based diet more efficiently without developing the intestinal problems observed with conventional strains of rainbow trout fed such diet. Increasing our understanding of how trout adapt to being fed plant-based diets will aid in the continued development of improved strains of trout.

Review Publications
Liu, K., Han, J. 2012. Enzymatic method for measuring starch gelatinization in dry products in situ. Journal of Agricultural and Food Chemistry. 60:4212-4221.

Overturf, K.E., Barrows, F., Hardy, R. 2012. Effect and interaction of trout strain (Oncorhynchus mykiss) and diet type on growth and nutrient retention. Aquaculture Research. 12:1–8. doi:10.1111/j.1365-2109.2011.03065.x.

Snyder, G.S., Gaylord, T.G., Barrows, F., Overturf, K.E., Cain, K.D., Hill, R.A., Hardy, R.D. 2012. Effects of carnosine supplementation to an all-plant protein diet for rainbow trout(Oncorhynchus mykiss). Aquaculture. 338-341:72–81.

Last Modified: 07/25/2017
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