Submitted to: Biological Agriculture and Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2013
Publication Date: 6/21/2013
Citation: Trosvik, K.A., Webster, C.D., Thompson, K.R., Metts, L.A., Gannam, A., Twibell, R. 2013. Effects on growth and body composition in Nile tilapia, Oreochromis niloticus, fry fed organic diets containing yeast extract and soybean meal as total replacement of fish meal without amino acid supplementation. Biological Agriculture and Horticulture. 29(3):173-185. Interpretive Summary: Protein is generally the most expensive component in an aquaculture diet, thus, diet manufacturers attempt to provide the minimum level of protein that will supply essential amino acids to fish. Fish meal (FM) is considered the most desirable protein ingredient for fish due to its high nutritional value and palatability; however, FM is the single-most expensive macro-ingredient (currently costing $US 1100-1400/ton) and is highly desired by other livestock industries. With static or declining fish populations that are used to produce FM, any negative disturbance, supply disruption, or availability problem, can lead to dramatic increases in the commodity price. Further, the capture of wild fish used to feed cultured fish is thought to be unsustainable by critics of aquaculture. Hence, it is essential to reduce or eliminate FM in diets to minimize diet costs. One approach to reducing FM from diets is to replace it with alternative, less expensive animal- or plant-protein ingredients, which will allow for continued expansion of the global aquaculture industry by utilizing renewable ingredients and help decrease diet costs. Soybean meal (SBM) is the most widely-used plant protein source in aquaculture diets and is known to be a cost-effective alternative for FM in diets for some aquaculture species because of its high protein content, relatively well-balanced amino acid composition, reasonable price, consistent quality, and steady supply. However, there are several disadvantages to using high percentages of SBM in diets for some fish which include: reduced levels of methionine and lysine; the presence of anti-nutritional factors, such as trypsin inhibitors and phytic acid; and reduced palatability if SBM is used at high percentages. Several studies have evaluated the effects of replacing FM on growth of tilapia, but complete replacement of FM with individual plant-protein sources has usually resulted in reduced growth. Nile tilapia, Oreochromis nicoticus, are widely produced globally with 4.5 million metric tons (MT) in 2012 due to numerous positive characteristics, including tolerance to crowding, high fecundity, fast growth, and high consumer demand. As tilapia are generally omnivorous/herbivorous in nature, prepared diets can utilize high percentages of plant protein ingredients, such as SBM; however, FM is usually added at high levels to hatchery diets used to feed newly-hatched and small (<50 g) tilapia. The objective of this study was to evaluate growth and body composition of Nile tilapia fry fed organic diets containing various percentages of organic soybean meal (OSBM) and yeast extract (YE), without added supplemental amino acids, as total replacements of FM. Results of a 6-week feeding trial indicate that diets containing 40% protein and formulated to contain 0% FM and various percentages of OSBM and YE resulted in reduced growth and feed efficiency of small Nile tilapia. However, fry fed a diet containing 0% FM, 40% YE, and 30% OSBM had 63% of the final weight of fish fed a diet of 20% FM. Thus, inclusion of OSBM and YE may have promise for use as a replacement for FM in practical diets for Nile tilapia fry. The identification and use of organically-certified ingredients as feasible protein sources for fish diets increases the potential for future organic certification and expansion of the organic aquaculture industry by reducing the reliance of FM diets; however, further study is warranted as diets with high percentages of SBM led to reduced growth and increased FCR values.
Technical Abstract: Fish meal (FM) is the main protein source in numerous aquaculture diets due to its palatability and quality. Quantities of FM have remained constant for the past several decades; however, demand has dramatically increased due to its inclusion in diets used for the global aquaculture industry. There are various alternative protein sources that can be used in aquaculture diets, with soybean meal (SBM) being the most-widely used plant-protein ingredient; however, use of SBM as the sole protein source has often resulted in reduced fish growth. There is a growing segment of consumers who desire organically-grown foods and since tilapia is one of the most-cultured fish in the world and have herbivorous/omnivorous feeding habits, tilapia fed an organic diet may allow producers to enter this rapidly-developing market. A feeding experiment was conducted to evaluate the combination of organic SBM and an organic yeast extract (YE) as complete replacements for FM. Five isonitrogenous, isocaloric diets were fed to small (0.1 g) Nile tilapia, Oreochromis niloticus, for 6 weeks. Diets contained various percentages (0, 10, 20, 30, and 40%) of YE, with Diet 1 formulated to be similar to a high-quality commercial diet containing 0% YE and 20% FM. At the conclusion of the feeding trial, fish fed Diet 1 had significantly (P < 0.05) higher mean final weight (3.99 g) and specific growth rate (SGR; 8.48%/day), and a lower feed conversion ratio (FCR; 1.40) compared to fish fed all other diets. Based upon the data, an organic diet which replaces FM with a combination of SBM and YE appears promising, but further research is needed to refine formulation so as to have similar growth performance with a FM-based diet.