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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Wildlife and Fisheries Science

First Advisor

Michael L. Brown


nile tilapia, yellow perch, diets, distillers, feeds


Aquaculture diets often account for >50% of the overall production costs for many aquaculture species, with the most expensive dietary constituent being protein. Generally, fish meal (FM) has been used as the primary protein source in diets, but rising costs and uncertain availability has generated much research in the use of alternative protein sources. Most of these sources consist of plant-based proteins that provide a primary carbohydrate-based energy source. Two such protein sources include distillers dried grain with solubles (DDGS) and commercially produced yeast cultures (i.e., probiotics). Increased production in fuel ethanol has led to larger quantities of fuel-based DDGS being produced. Therefore, this co-product provides a potentially low-cost protein alternative, while yeast cultures may simultaneously promote increased growth and health of fish. Also, relatively few studies have looked at the potential links between extrusion parameters and the corresponding growth of fish fed extruded diets. To address the use of DDGS and yeast cultures in aquaculture diets, three feeding trials were performed that incorporated these constituents into diets fed to Nile tilapia Oreochromis niloticus and yellow perch Perca flavescens. However, before performing these feeding trials, a literature review was conducted to evaluate the nutritional requirements needed by both species and the nutritional and chemical properties of DDGS and yeast cultures in order to create appropriate experimental diets for testing. The first feeding trial was performed to investigate inclusion of DDGS as a FM replacement for juvenile Nile tilapia [34.9 ± 1.4 g (mean ± SE)]. Six isocaloric (4.43 ± 0.20 kcal/g), isonitrogenous (39.3 ± 0.4% crude protein) experimental diets were formulated to contain 0 (reference diet), 17.5, 20, 22.5, 25, and 27.5% DDGS. The reference diet resulted in significantly higher weight gain (WG), food conversion ratio (FCR), and protein efficiency ratio (PER) than experimental diets except for the 17.5% DDGS diet which provided similar FCR and PER. The diet containing 27.5% DDGS had significantly lower FCR and PER values than all other diets even though apparent digestibility did not significantly differ among experimental diets. Correlation analyses indicated a significant, negative correlation between the water activity index and digestion of crude protein rates indicating the potential role of extrusion on fish digestion rates. Although no statistically greater than the other diets, 20% DDGS provided the highest apparent WG among experimental diets, while 17.5% promoted the best FCR and PER. The use of diets containing 17.5% or 20% DDGS may offset the higher costs of a FM-based diet provided that adequate growth is achieved during the production period. The second feeding trial was performed with juvenile Nile tilapia to investigate the use of a commercially produced yeast-based probiotic in combination with DDGS to assess growth, feed use, and stress resistance. A two by three factorial design was used to produce six isocaloric (2.32 ± 0.09 kcal/g), isonitrogenous (28.03 ± 0.03% crude protein) experimental diets containing 20, 25, and 30% DDGS by weight, with or without 0.125% probiotics. Aquaria (110-L) were stocked with eight Nile tilapia (43.6 ± 1.3 g) with four replicates per diet. Weight gains, FCR, PER, plasma cortisol levels, and survival rates did not significantly differ among fish fed differing DDGS levels or between similar DDGS levels with or without probiotics. Correlation analyses indicated relationships between feeding efficiency (i.e., FCR and PER) and Hunter b* color values indicating the potential use of feed color values as potential estimators of the overall feed efficiency of fish fed aquaculture diets containing DDGS. Results indicated that the inclusion of probiotics did not increase the use of DDGS or enhance the growth or stress resistance of juvenile Nile tilapia. The third feeding trial was performed to investigate inclusion levels of DDGS and soybean meal (SM) used in the diets of juvenile yellow perch. Six isocaloric (3.22 ± 0.02 kcal/g), isonitrogenous (30.1 ± 0.2%) experimental diets were formulated to contain 0% + 31.5%, 10% + 26%, 20% + 20.5%, 30% + 15%, 40% + 9.5%, and 50% + 4% DDGS + SM, respectively. Fish fed 40% DDGS + 9.5% SM exhibited the highest WG and heptasomatic index (HSI) values, while fish fed diets with 20% + 20.5% and 30% + 15% DDGS + SM exhibited statistically similar WG. Fish fed 50% DDGS + 4% SM had statistically lower WG, Fulton condition, and apparent digestibility values than all other fish. Crude protein and lipid levels of fish did not significantly differ among female or male yellow perch fed differing concentrations of DDGS and SM, but significant differences did occur between female and male crude protein and lipid concentrations when fed 10% DDGS + 26% SM and 20% DDGS + 20.5% SM, respectively. Correlation analyses indicated significant relationships between FCR and Hunter L* and a* color values and between compressive strength and apparent digestibility. These correlations may provide predictive insight in the potential condition and digestibility of fish fed plant-based aquaculture diets. Results indicated that yellow perch can use up to 49.5% plant-based proteins (DDGS + SM) without negatively affecting growth, feeding efficiency, and muscle composition. In conclusion, these studies demonstrate that inclusion of DDGS within the diets of aquacultured species is viable and may help to offset dietary costs. However, varying results between species, along with moderately lower growth in juvenile Nile tilapia, indicates that further research is needed on the inclusion of fuel-based DDGS. Also, it appears that the extrusion process may play a role on the overall performance of fish, but results presented here are preliminary and more research is needed. (See more in text.)

Library of Congress Subject Headings

Nile tilapia -- Feeding and feeds
Yellow perch -- Feeding and feeds
Distillers feeds
Proteins in animal nutrition
Extrusion process
Distilling industries -- By-products


Includes bibliographical references (page 80-102)



Number of Pages



South Dakota State University


Copyright © 2009 Travis W. Schaeffer. All rights reserved.