Location: Aquatic Animal Health Research2012 Annual Report
1a. Objectives (from AD-416):
The overall objective of this project is to define the nutritional value and nutrient bioavailability of various protein and oil sources to improve feed formulations, decrease feed costs for channel catfish and tilapia and increase the use of U.S. agricultural products/byproducts. Efficient feeding practices to improve fish performance and health will be developed for improved formulations. Objective 1: Determine the nutritional value and nutrient bioavailability of various protein sources (especially distillers' dried grains with solubles (DDGS)) and essential fatty acids and their effects on growth, feed palatability, stress, immune response and disease resistance. Objective 3: Develop feeds and feeding strategies to improve nutrient retention, production efficiency, product quality and fish health.
1b. Approach (from AD-416):
The U.S. aquaculture industry faces numerous challenges including high feed and energy costs, low-cost imports and lower fish prices paid to producers. Among these, feed cost represents the largest expenditure in aquaculture operations, and protein is the most expensive component in fish feeds. Lower cost alternative protein sources to replace fish meal and other expensive protein sources must be identified. Soybean meal (SBM), because of its low-cost, availability, consistent quality, and high nutritional value, is the most commonly used plant ingredient in fish feeds, comprising up to 45% grow-out diets. Distillers' dried grains with solubles (DDGS) is readily available and less expensive than SBM and other conventional protein sources on a protein-cost basis, but its use in fish feeds is very limited. Replacement of SBM or more costly ingredients by DDGS would reduce feed costs. This proposed project will investigate the nutritional value and nutrient bioavailability of DDGS derived from various grain sources, and corn DDGS from ethanol plants for channel catfish and tilapia, define the essential fatty acid (EFA) requirement, optimum ratio of n-3 to n-6 and their effect on gene and protein expression, identify biologically active compounds in DDGS which may improve fish growth and health, and develop least-cost feed and feeding strategies to improve nutrient retention, product quality and health. This project should lead to reduced feed costs, increased use of DDGS, and improved feeding practices which will lead to improved growth and survival and product quality, lower producton costs, as well as increased demand of DDGS.
3. Progress Report:
A 10-weeks feeding study to determine the essential fatty acid (EFA) requirement of male hybrid tilapia was conducted using a control diet with 6% coconut oil (diet 1) and nine test diets containing different levels and proportions of linoleic acid (LA, n-6) linolenic acid (LN, n-3). Fish fed the control diet deficient in LA and LN had the poorest growth and feed efficiency (FE). Similar performance was obtained in fish fed other diets. Analysis of whole body lipid showed that tilapia accumulated higher levels of n-6 than n-3 as the body ratios of n-6 to n-3 were higher than dietary ratios. Dietary treatments had no effect on hematological and immunological parameters and the resistance of fish to bacterial (Streptococcus (S.) iniae) infection. This study indicates that both LA and LN are dietary essential for juvenile hybrid tilapia. However, compared to LN, LA appears to have a better growth promoting effect. Dietary LA alone can meet the EFA requirement of hybrid, and a level of 1.14% of diet is required for optimum growth. Another 10-week study evaluated the nutritional value of distiller's dried grains with solubles (DDGS) from various sources (3 corn DDGS, 1, 2, and 3, 1 whiskey DDGS, 1 sorghum DDGS and 1 wheat DDGS) as replacements of one-third of protein supplied by soybean meal + corn meal. Fish fed diets containing corn DDGS 2 and 3 had significantly higher weight gain than those fed the control diet and diets containing corn DDGS 1, sorghum DDGS and wheat DDGS. This variable did not differ among fish fed other diets. This growth improvement was due to improved feed intakes since FE did not differ among all treatments. The source of dietary DDGS has no influence on hematological variables, serum immune responses and the resistance of fish to S. iniae infection challenge. Another study evaluating the nutritional value of different fractions of by-products from ethanol distillery [DDGS, distiller's dried grains (DDG), distiller's solubles (DS) and DDG + DS] as replacement of one-third of protein supplied by soybean meal + corn meal was conducted with channel catfish. Preliminary results showed that feed consumption was essentially the same for all diets but fish fed diets with DS or DDG + DS had better weight gain and FE than fish fed other diets. The differences, however, were not always significant. Fish fed diets containing distillery by-products appeared to have more resistance to the Flavobacterium columnare challenge. A similar study with all-male tilapia hybrid is currently on-going.