|Koch, Joao - Universidade Estadual Paulista (UNESP)|
|Rawles, Steven - Steve|
|Cummins, Vaun - Kentucky State University|
|Kobayashi, Yuka - Kentucky State University|
|Thompson, Kenneth - Kentucky State University|
|Gannam, Ann - Us Fish And Wildlife Service|
|Twibell, Ron - Us Fish And Wildlife Service|
|Hyde, Nathan - Us Fish And Wildlife Service|
Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/2015
Publication Date: 11/14/2015
Citation: Koch, J.F., Rawles, S.D., Webster, C.D., Cummins, V., Kobayashi, Y., Thompson, K.R., Gannam, A.L., Twibell, R.G., Hyde, N.M. 2015. Optimizing fish meal-free commercial diets for Nile Tilapia, Oreochromis niloticus. Aquaculture. 452:357-366.
Interpretive Summary: One method of optimizing commercial diets for tilapia is to target the nutrient levels found in a typical diet containing fish meal. Then fish meal is replaced in the formula with a less expensive protein, and supplemental nutrients as needed, in order to make the replacement diet perform as well as the fish meal diet. An alternate method, called Ideal Protein Theory, uses the average nutrient levels in the fish being grown as the targets for diet formulation instead of the levels found in a fish meal control diet. Our goal was to compare the two methods of diet formulation for optimizing commercial tilapia diets. Our control diet was a high quality practical formula containing protein from menhaden fish meal and soybean meal. Seven test diets were formulated by replacing fish meal in the control diet with different ratios of poultry by-product meal and soybean meal. The amino acids methionine and lysine were added to the seven test diets to match the levels measured in the fish meal control diet (first method). The amino acid taurine was also added at 1% to six of the seven test diets to test whether taurine is essential for tilapia, as it is in some fish species when fed high plant-protein diets. The test diets were formulated using the latest nutrient digestibility data for the ingredients used in the test diets. However, because digestibility data were not available for all ingredients in the test diets, some differences in diet performance were noted that illustrated the need for more research on ingredient nutrient availabilities for tilapia. The results suggest that using the nutrient profile of a fish meal control diet as the target for optimizing fish meal replacement diets is inadequate; whereas using Ideal Protein Theory – the whole body nutrient pattern of tilapia—is a more useful formulation target. Finally, while the database of ingredients that have been evaluated in tilapia is growing, the industry can benefit from more research in tilapia on the nutrient composition and digestibility of a variety of traditional and new ingredients.
Technical Abstract: A feeding trial was conducted in a closed recirculating aquaculture system with Nile tilapia Oreochromis niloticus juveniles (mean weight, 6.81 g) to examine the response to a practical diet containing protein primarily from menhaden fish meal (FM) and soybean meal (SBM) (control, Diet 1) or to diets with decreasing ratios of PBM to SBM (Diets 2-7; dose-response) as a total replacement for digestible protein from FM, and the efficacy of 1% supplemental taurine (Tau) at the highest level of plant protein inclusion by removing Tau (Diet 8). To the extent possible, the replacement diets were formulated using currently published amino acid availabilities for the ingredients of interest in order to estimate and supplement the first two limiting amino acids (Met and Lys) to match levels in the FM control diet. The test diets were formulated to contain 35% digestible protein. Fish were fed three times daily all they would consume in 30 min. All performance measures were quadratic with respect to PBM: SBM ratio in the diet. The highest weight gain, lowest average daily feed intake, lowest feed conversion, and greatest specific growth rate coincided with a dietary PBM:SBM ratio of 1.22 to 1.35 suggesting the best tilapia performance in the current trial was achieved with replacement formula D3 that contained approximately 20% SBM, 30% PBM, and supplemental Lys, Met, and Tau. However, all growth performance measures were significantly linear and decreased with respect to increasing distance from the ideal protein amino acid profile for tilapia. Positive effects of taurine supplementation at the highest level of dietary plant protein inclusion were not observed and may have been overwhelmed by imbalances in other amino acids in the test diets. The current results provide evidence that total deviation from the ideal protein profile in tilapia is an important consideration for diet formulation when combinations of diet ingredients are used. Hence, the essential amino acid content of a fish meal control diet may be an inadequate target for optimizing fish meal replacement diets for tilapia; whereas the whole body or muscle amino acid pattern may be a more useful formulation target. Finally, while the database of ingredients that have been evaluated in tilapia is growing, the industry will benefit from more efficient diets as long-term averages of amino acid composition and digestibility accrue for a variety of traditional and novel ingredients.