Location: Aquatic Animal Health Research2010 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 12-week feeding study with sexed-reversed male Nile tilapia using a control diet and the control diet supplemented with 1.0 and 2.0% of brewers yeast or grobiotic showed that weight gain, feed consumption and survival were not affected by dietary treatments, but fish fed the diet with 1% grobiotic had significantly lower feed efficiency than those of other treatments. Whole body proximate composition was not affected by dietary treatments. Serum lysozyme, protein, total immunoglobulin and antibody titer were not affected by yeast or grobiotic supplementation. Serum alternative complement was significantly higher in fish fed the diet 1.0% yeast. Mortality 20 days post challenge with Streptococcus iniae, although not statistically different, tended to be lower in fish fed yeast or grobiotic-containing diets. A study evaluating the effects of dietary levels of potassium diformate (KDF) using mixed-sex tilapia indicated that survival at the end of week 12 did not differ among fish fed different diets. Weight gain and feed efficiency of fish fed the diet with 1.00% KDF were significantly higher than those fed diets with 1.25 or 1.50% KDF, but were not different from those fed diets with 0, 0.25, 0.50 or 0.75% KDF. Feed intake was highest and lowest for fish fed 0.75% and 1.50% KDF diets, respectively. There were no treatment differences among hematological parameters and innate immune responses (serum protein, immunoglobulin, lysozyme and alternative complement). Mortality 14 days post-challenge with S. iniae and antibody titer against the same bacterium was also not affected by dietary treatments. In another study, the same experimental diets were fed to all male tilapia for 10 weeks. Weight gain, feed intake and feed efficiency did not differ among treatments, but these variables tended to be lower in fish fed diets with 0.75% or higher KDF. The diet with 0.50% KDF provided numerically the highest weight gain and feed efficiency (6.9 and 6.5% better than those of the control diet, respectively). Serum protein and total immunoglobulin were similar in all treatments. Lysozyme activity was lowest in fish fed the 0.75% KDF diets. Dietary levels of KDF, however, had no effect on the resistance of tilapia to Streptococcus iniae challenge.
1. Dietary Supplementation of Brewers Yeast and Grobiotic to Improve Growth and Disease Resistance of Tilapia. Dietary supplements such as immunostimulants and prebiotics hold promise as a potential replacement of antibiotics in improving growth and maintaining fish health. We evaluated the efficacy of two commercial prebiotics (brewers yeast and grobiotic)each at 0, 1.0 and 2.0% levels for a period of 12 weeks. This study revealed growth, feed intake and efficiency, body proximate composition and serum protein, immunoglobulin and lysozyme activity were not affected by dietary treatment. Alternative serum complement was higher in fish fed the 1.0% yeast. Mortality data, though not statistically significant, were lower in the groups fed diets supplemented with yeast or grobiotic. These products appear to have potential for use to improve the disease resistance in Nile tilapia, but more research is needed.
2. Growth and Disease Resistance of Mixed-sex Tilapia Fed Diets Supplemented with Potassium Diformate. Short-chain organic acids or their salts have received much attention as alternatives to antibiotics. Among these, potassium diformate (KDF) has been shown to be an effective growth stimulator in diets of pigs, but its effects on aquaculture species are inconsistent. Thus, this study was conducted to evaluate the effects of dietary levels of KDF on growth, feed utilization, hematology, immune response and resistance of mixed sex Nile tilapia to Streptococcus iniae challenge. The results showed a trend of increased weight gain of Nile tilapia with increasing dietary levels of KDF from 0.25 to 1.0%, but levels of 1.25% or higher adversely affected weight gain and feed efficiency. However, dietary inclusion of KDF has no effect on hematological parameters, immune responses and the resistance of fish against S. iniae challenge.
3. Growth and Disease Resistance of All-male Tilapia Fed Diets Supplemented with Potassium Diformate (KDF). It is commonly known that male tilapia grow faster than females. Thus, the non-significant effect of KDF obtained from our previous study (mixed-sex) may be related to the differences in the ratio male to female present in various replicate tanks. Another study was conducted with all male tilapia employing the KDF-containing diets used in earlier study. This study revealed that weight gain, feed intake and efficiency were not significantly affected by adding KDF at levels 0 to 1.5% of diet. However, these variables tended to be lower in fish fed diets with 0.75% or higher KDF and the diet with 0.50% KDF provided 6.9 and 6.5% better growth and feed efficiency, respectively compared to those of the control. Dietary levels of KDF, however, had no effect on the resistance of tilapia to Streptococcus iniae challenge. The discrepancy among data on the beneficial effects of inclusion of KDF in tilapia diets may be due to variations among fish species, strain, sex, size or age, levels of inclusion, composition and nutrient content of experimental diets, buffering capacity of dietary ingredients, culture and feeding management, and water quality. It is suggested that more research be conducted to better understand and ascertain the mechanism of the potential beneficial effect of this compounds in diets of tilapia as well as of other species.
Lim, C.E., Aksoy, M., Li, M.H., Welker, T.L., Klesius, P.H. 2009. Growth performance, immune response and resistance to Streptococcus iniae of Nile tilapia fed diets containing various levels of vitamins C and E. Journal of the World Aquaculture Society. 41: 35-48.