Nile Tilapia: Replacing Fish Meal With Soybean Meal And Yeast

Introduction

Aquaculture, or fish farming, is the fastest-growing agricultural sector in the United States, with annual growth rates of more than six per cent for the past two decades. Globally, fish made up 15 per cent of the average per capita animal protein intake in 2007; aquaculture supplied close to 50 per cent of this demand. Total value of various aquaculture products is shown in Figure 1. Future trends project aquaculture production will continue to rise largely due to the fact that the oceans are being overfished and are reaching their maximum production capacity.

Figure 1: Total value of various US aquaculture products (data adopted from FAO 2009).

While numerous efforts have been done to preserve the wild fisheries in recent years, there continues to be strong pressures on a variety of wild fish stocks. As the human population continues to expand worldwide, it is essential that seafood supply comes from aquaculture.

In the US, consumption of tilapia, catfish, salmon and shrimp has boosted the percentage of seafood being produced by aquaculture. However, it should be noted that much of the higher supply to meet this growing demand is imported. Clearly, US producers face strong competition from foreign producers around the world. Therefore, it is essential that domestic producers continue to develop new products and increase production efficiencies of rising aquaculture products, such as tilapia, to compete economically with producers overseas.

Tilapia are tropical fish endemic to freshwater in Africa, Jordan, and Israel and are being cultured in virtually all types of production systems in both fresh and saltwater in tropical, subtropical and temperate climates. Tilapia have a long history of use as a food source; ancient Egyptians used to feed tilapia that were being held in cages waiting to be taken to market, and it has been speculated that tilapia were the fish from the biblical parable of the loaves and the fishes. Since then, tilapia have been introduced world-wide and production has grown to over 2.2 million metric tons in 2007, with an approximate production level of three million metric tons in 2010, making it one of the most important farm-raised finfish globally. Tilapia’s acceptance by consumers worldwide is shown on Figure 2, where the annual growth rates are almost twice as big as the overall aquaculture rates. In 2007, tilapia was estimated to be the 4th most consumed finfish in the United States. This wide- spread success is due, in part, to their high level of adaptability and the ease of production.

Tilapia have sometimes been called “aquatic chicken” due to their rapid growth rates; high-quality flesh; tolerance to disease; adaptability to virtually all types of production systems in tropical to temperate climates; and ability to grow and reproduce in captivity. Currently, they are the second-most produced group of food fish globally (behind carps), and the growth trend is likely to continue.

Figure 2: Overall annual growth rates of tilapia and aquaculture worldwide.

To date, the vast majority of tilapia consumed in the US is produced in China, and Central and South America; however, increasing positive attitude toward local, organically-produced seafood may cause US production of tilapia to rise. Tilapia are produced in intensive production systems, and as a result, it has become important to evaluate diets that are economically and environmentally- sustainable, as well as nutritionally-complete.

Because diet costs make up the largest expense (40 to 80 per cent of operating expenses) of an intensive aquaculture enterprise, it is essential to evaluate low-cost, nutritious diets to increase profitability for tilapia producers. This could lead to expansion of tilapia farming in the US Currently, fish meal (FM) constitutes a substantial part of a commercial diet formulation of tilapia fry. FM is considered the most desirable animal protein ingredient in aquaculture diets because of its high protein content, balanced amino acid profiles, high digestibility and palatability, and as a source of essential omega-3 (n-3) polyenoic fatty acids.

However, FM is one of the most expensive macro-ingredients (used in high percentages) in an aquaculture diet currently costing $900-1100 per ton. With the 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 FM prices. The high cost of FM and concerns regarding its future availability have made it imperative for the aquaculture industry to reduce or eliminate FM from fish and crustacean diets.

One approach aquaculture nutritionists have embraced is to partially or totally substitute FM with alternative protein sources which will alleviate the dependence on marine-derived protein sources, allow for continued expansion of the global aquaculture industry by utilizing renewable ingredients, and possibly decrease diet costs, thereby potentially increasing profits for tilapia producers. It has been found that the use of two or more complimentary protein sources in addition to amino acid, vitamin and mineral supplementation may allow for growth results similar to those found when FM is the primary protein source.

There have been many studies focused on finding protein replacements for fish meal in fish diets. Some of these fish meal replacement candidates include soybean and cottonseed meals, grains, yeast and rendered animal meals. Plant proteins have the advantage of being sustainable, highly available and lower-cost due to their worldwide production. Soybean meal (SBM) is the most widely-used plant protein source in aquafeeds and is known to be a cost-effective alternative for high-quality FM in diets for many aquaculture species because of its high protein content, well-balanced amino acid profiles, reasonable price, consistent quality, and steady supply. It has been well documented that SBM has one of the best amino acid profiles of any plant protein feedstuff. However, a diet containing SBM as the sole protein source might be nutritionally incomplete since methionine and lysine are the most limiting amino acids in high-SBM diets.

The use of sustainable, alternative protein sources, such as plant and yeast meals, provides the opportunity for the use of organic diets in aquaculture. Organic agriculture is the fastest growing food production industry in many countries and the sale of organic products increase revenue for producers up to 20per cent higher than non-organic counterparts. In the US, the value of organic agriculture is estimated to be $30 billion annually. However, in order for tilapia to be labeled as organic, they must be fed an organic diet.

In order to evaluate use of organic diets for tilapia, a study was conducted to assess organic yeast (OY) in combination with organic SBM (OSBM) as complete protein replacements for FM in diets for Nile tilapia. Fish meal is not considered an organic protein source.

One control diet was formulated similar to a commercially- available tilapia diet, while eight experimental diets were formulated to contain organic soybean meal (OSBM) and various levels of organic yeast (OY; 15, 30 and 45 per cent), with and without amino acid (AA) supplementation of methionine and lysine, as replacements for menhaden fish meal (FM; Table 1). Diets were extruded into spaghetti-like strands using a 0.5-cm die and air-dried (Figure 3). Once all diets had dried completely, portions of each diet were stored in plastic bags and stored in a freezer until fed.

The feeding trial was conducted using a recirculating aquaculture system, comprised of aquaria that drained into a biofilter (Figure 4). Nile tilapia averaging 0.11 g were stocked into each aquarium at 20 fish per aquarium (36 aquaria total). Each aquarium was assigned one of the nine diets. Tilapia was fed three times daily (0800, 1200 and 1600 h) all the diet they could consume for thirty minutes for six weeks (Figure 5).

After six weeks, final mean average weight of fish fed Diet 1 (20 per cent FM and 50.3 per cent SBM) and Diet 9 (0 per cent FM, 33.8 per cent organic soybean meal [OSBM], and 46.5 per cent organic yeast [OY]+ the amino acids [AA] lysine and methionine) was significantly higher (4.98 and 4.96 g) than fish fed all other treatment (diets) (Figure 6). Final mean weight increased with increasing OY inclusion in both the non-amino acid-supplemented and the supplemented treatment groups.

Table 1. Ingredient composition of the nine practical diets containing various levels of soybean meal and yeast extract fed to Nile tilapia fry. All ingredients were certified organic in Diets 2-9. Diets marked with an asterisk (*) were supplemented with methionine and lysine amino acids (A.A.).

These are the first data evaluating the use of organic SBM and OY as total replacement for FM in Nile tilapia fry. Results indicate that a diet containing 40per cent protein and formulated to contain 0per cent FM, 33.8per cent OSBM, and 46.5per cent OY, with supplemental methionine and lysine, may be sufficient for Nile tilapia fry as this diet produced as much growth as the commercial diet. While information about specific nutritional requirements and practical diet formulations for tilapia has been widely studied, there is little information on the partial or total replacement of FM with less expensive organic plant protein sources.

Replacement of FM with less expensive protein sources, such as OSBM and OY, may help contribute to a reduction in diet costs and thereby increase profit for producers. In addition, organically-grown tilapia may offer a broader marketing-base for tilapia producers, while at the same time increase the value compared to traditional non-organically grown products. This study could lead to domestic production of certified organically-grown tilapia which might allow farmers to market a product that foreign competitors do not currently have, and at the same time, allow for the use of domestic SBM. Further studies need to be conducted on the use of SBM,as a FM replacement in tilapia diets.

Figure 3: Tilapia diets being prepared for the study.

Figure 4: The experimental aquaria system used in the study.

Figure 5: Top picture shows tilapia being fed in the aquaria while the photo at the bottom are the tilapia fry.

Figure 6: Tilapia diets being prepared for the study.