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Aquaculture Feed and Fertilizer Resources Information System
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Algae as a live food
Shrimp larvae are found naturally as a part of the zooplankton, beginning as herbivores but soon becoming omnivores with a preference for zooplankton. Live feeds are commonly used in shrimp larval rearing to postlarval stage. Algae are readily consumed from Zoea 1 until Postlarvae 2 (Evans, 1992) (Figure 21).  - Figure 21. Mass algal culture from test tubes of pure strains (courtesy of Laurence Evans)
Formulated feed – feed ingredients
Together with the nutrient requirements of shrimp, it is imperative to know the proximate composition of feedstuffs to be able to formulate a diet to meet these needs. The moisture content, crude protein, crude lipid, crude fibre, nitrogen-free extract (digestible carbohydrates), ash content, vitamins and minerals, available phosphorus, amino acid content and levels of polyunsaturated fatty acids of the n–3 and n–6 series should be known for each feed ingredient (Piedad–Pascual, 1989a). Plant proteins can be deficient in key amino acids when compared with fishmeal (Table 15) (Ahamad Ali, Syama Dayal and Ambasankar, 2004).
A variety of plant and animal feedstuffs is used in shrimp feeds (Table 13a, Table 13b). A combination of feed ingredients is needed to supply the nutrients and energy shrimp need for best growth. The percentage inclusion of each feed ingredient is determined by factors such as feedstuff proximate composition, amino acid profile, shrimp nutrient requirements, ingredient cost, availability of each ingredient, feed digestibility and processing characteristics.
The major components of a typical 35 percent protein shrimp diet are wheat flour (35 percent), soybean meal (20 percent) and fishmeal (25 percent) (Hunter and Chamberlain, 2006) and perhaps yeast. These ingredients provide the protein, amino acids and energy in the diet. Protein supplements are sourced from animal, yeast or plant proteins. Raw materials that have proven to be excellent major protein sources for shrimp diets include squid, soybean meal, shrimp meal, fishmeal, krill and scallop waste (New, 1976; Venero, Davis and Lim, 2008).
Fishmeal
Marine shrimp aquafeed diets included 35 percent fishmeal content in 1995, 25 percent in 2000 (Tacon, 1998) and approximately 25 percent in 2007 (Venero, Davis and Lim, 2008). Commercial shrimp diets typically contain approximately 25 percent fishmeal (Tacon and Barg, 1998), and there is a trend towards lower inclusion levels. Fishmeal is a rich source of high quality protein, has relatively high-energy content and is rich in important minerals such as phosphorus, B vitamins and essential fatty acids.
The shrimp feed industry mainly uses high quality (premium grade: prime or super prime) fishmeal imported from Chile or Peru (FAO, 2007b). Rancidity from lipid oxidation, which may occur during storage, is one of several factors affecting fishmeal (Laohabanjong et al., 2009). Ricque–Marie et al. (1998) found that fresh fishmeal gave better growth in all shrimp species tested.
Fish oil
Fish oils and squid oils provide essential fatty acids required by shrimp (FAO, 2007b). Fish oil inclusion averaged 3 percent of the diet in 1995 and 2 percent in 2000.
Wheat
This ingredient is used as a binder in pelleted shrimp and prawn feeds (FAO, 2007b) and a carbohydrate source. Pelleted feeds require a minimum of 20 percent starch from cereal grains to improve water stability (Chamberlain and Bortone, 2006). Ideally, wheat should have high gluten content. A low wet gluten index (23 to 28 percent) relative to the ideal index for shrimp feed pelleting (32 percent to 35 percent) (Suresh, 2007) would require wheat gluten or other binders to achieve the necessary pellet water stability.
Soybean meal
Soybean meal has one of the best essential amino acid profiles of all protein-rich plant feedstuffs (Fox, 2008a). Soybean meal with hulls (44 percent crude protein) and dehulled soybean meal (48 percent crude protein) are available in large quantities. These products are used in shrimp and prawn feeds (FAO, 2007b). Marine shrimp appear to be able to digest soybean meal very efficiently. Other feedstuffs
Other plant protein sources such as cottonseed meal, peanut meal, canola meal, distillers grain with solubles, some legume meals (Bautista–Teruel, Eusebio and Welsh, 2003; Venero, Davis and Lim, 2008), coconut cake, Spirulina (Ahamad Ali, 1992) and gingely can be used, depending on local availability, nutrient profile and price (Table 13a). The limitations in the use of plant proteins include deficiency or imbalance of essential amino acids, presence of antinutritional factors or toxins and low palatability. With concerns about mycotoxins, groundnut cake is not used in shrimp feeds in India (FAO, 2007b) (Table 13b). Yeast (brewers and molasses) is used in shrimp feeds (FAO, 2007b).
Soybean lecithin (Table 2d) is a source of phospholipids such as phosphatidylcholine and phosphatidylinositol) in aquafeeds and is used in P. indicus diets at 0.5 to 2 percent (Table 4) (Lim and Sessa, 1995). The recommended inclusion levels are 0.5 to 1.0 percent for deoiled and 1.0 to 2.0 percent for fluid lecithin. A typical cholesterol inclusion level is 0.1 percent, the balance being provided by the raw materials (Hunter and Chamberlain, 2006).
Other protein sources include poultry by-product meal (Menasveta and Yu, 2002; Amaya, Davis and Rouse, 2007a,b; Cruz–Suárez et al., 2007).
Premixes
Vitamin and mineral premixes are generally added to shrimp feeds (see “Ash and Minerals” and “Vitamins” above). Inclusion levels are in the region of 0.1 to 1 percent for minerals and 0.1 to 0.5 percent for vitamins (Hunter and Chamberlain, 2006) (Tables 8 and 9). Vitamins have variable stability, so a stored feed slowly loses its vitamin content.
Binders
Aquaculture feeds and especially shrimp feeds need to be water stable. Shrimp feed also needs to sink, as shrimp feed off the substrate. Binders are often used to achieve the necessary water stability (Lim and Cuzon, 1994; Hunter and Chamberlain, 2006). Urea formaldehyde, wheat gluten and gelatine are common binders used in shrimp feed (Table 6). Gelatine and gluten are highly digestible and contain protein. Urea formaldehyde is not permitted in feeds in the European Union (EU) and the United States of America (USA), so wheat gluten and gelatine are real options in these regions (De Muylder, Hage and van der Velden, 2008). Starch gelatinization of ingredients like wheat is also necessary. Raw material particle size, pellet die thickness, controlled preconditioning temperatures and durations and post-conditioning or extrusion are important pellet production technologies to maximize starch gelatinization and to improve binding and pellet water stability (Oblado et al., 1998).
Attractants
Crustacean or krill meals are good feed attractants (50 g/kg inclusion) (Smith et al., 2005). Products like crab meal, krill meal, shrimp head meal and shrimp shell meal are included at about 3 to 5 percent (Hunter and Chamberlain, 2006).
Krill oil and meal are high in omega–3 bound phospholipids and astaxanthin. At an 11 percent inclusion of krill in the diet, fishmeal can be significantly reduced, fish oil at least halved and soya lecithin and cholesterol excluded from shrimp formulations, going by research with P. vannamei (Baevre-Jensen and Nunes, 2008). The cost of krill needs to be offset against these savings.
Squid liver powder (1 to 3 percent), squid meal (1 to 3 percent), fish hydrolysates (2 to 5 percent) and fish solubles (2 to 5 percent) can all serve as attractants. Squid products have a good amino acid and fatty acid profile and are a shrimp growth promoter (Hunter and Chamberlain, 2006). Other additives
Hunter and Chamberlain (2006) list the use of enzymes, growth promoters, health additives (immunostimulants, probiotics, vaccines) and toxin absorbers, but none of these are widely or standardly incorporated or well researched at present.
Commercial synthetic antioxidants and mould inhibitors (sodium or calcium propionate, 0.05 to 0.15 percent) are also added to the diet. Butylated hydroxytoluene (BHT) (250 to 500 ppm), butylated hydroxyanisole (BHA) (250 to 500 ppm or 0.01 to 0.02 percent of fat content) and ethoxyquin (125 to 150 ppm) are used. Paradigmox Green from Kemin is an ethoxyquin-free antioxidant that can be used as an antioxidant in shrimp feeds certified for use in organic aquaculture.
Feed equipment
Refer to http://www.feedmachinery.com/glossary/ for an example of the equipment used in a feed mill. The shrimp pelleting technology is described by Tan and Dominy (1997).
Feed manufacturing – the pelletizing process
See FAO (2001b), “Aquaculture Development. 1. Good Aquaculture Feed Manufacturing Practice” for technical guidelines for good aquaculture feed manufacturing practice. Feed manufacturing creates a compound feed with a balanced mixture of feedstuffs and feed additives in a form suitable for the target species (Kearns, 2008).
Milling of feedstuffs to 124 µm particle size before pellet manufacture influences pellet water stability, pellet durability, starch gelatinization, shrimp live weight and weekly weight gain (Obaldo et al., 1998). The energy required to grind was lowest at 586 µm or coarser particle size. Air-swept pulverizers are usually used in shrimp pellet mills and produce fine grinds of 95 percent minus 250 μm. Fine-grind hammer mills can grind product to 90 to 95 percent minus 420 μm (Bortone, 2005) or at best 300 µm (Chamberlain and Bortone, 2006). After grinding, 95 percent of the feed ingredients should be less than or equal to 250 µm (Tan and Dominy, 1997) and for smaller shrimp, 150 to 180 µm (Chamberlain and Bortone, 2006). In shrimp feed mills, ingredients are ground after weighing and mixing, providing a more uniform particle size distribution (Chamberlain and Bortone, 2006).
The sinking property of a feed is determined by its bulk density. Finished feed needs to weigh over 600 to 640 g/litre in order to sink (Rokey, 2004; Kearns, 2008). The pelleting process requires a die with a compaction ratio of between 18 (Tan and Dominy, 1997) and 24 (Chamberlain and Bortone, 2006) (if the die holes are between 2.2 and 2.5 mm, the die thickness should be 40 to 45 mm).
Good mixing is a critical and important process in the feed mill (Chamberlain and Bortone, 2006). Oils and lecithin need to be added after the binders such as wheat gluten and water to effect binding, as the oils coat binders and make them ineffective.
Most commercial shrimp feeds are manufactured by pelletizers (Lim and Cuzon, 1994; Chamberlain, 2004). Extended preconditioning is a standard method to produce water-stable feed, as it allows time for heat and moisture to begin the process of starch gelatinization before the raw material mix is pelletized (Figure 22). The moisture content of pellets exiting the die should be 16 to 17 percent at 90 to 100 oC. Postconditioning (at least 10 minutes at 90 oC) improves pellet water stability by 30 to 40 percent through improved starch gelatinization (Chamberlain and Bortone, 2006). Practical adjustments to improve water stability are (Lim and Cuzon, 1994; Kearns, 2008): - Increase starch levels (must be gelatinized in the processing)
- Increase functional proteins
- Increase use of binders
- Reduce internal fat levels and add the fat externally
- Reduce fibre levels in the formula
- Adjust extrusion/pelletizing moisture levels
- Increase specific mechanical energy inputs (e.g. pelletizer die thickness)
- Increase specific thermal energy inputs (added dry steam)
- Increase retention time in both the preconditioner and extruder/pelletizer barrel
- Adopt equipment-specific technologies such as the Wenger Extrusion Density Management System
- Postconditioning and drying after pelletizing
- Handling of product
Some mills add oils, top dressing pellets with fish oil after drying and cooling (Chamberlain and Bortone, 2006), but in most cases, oils are a part of the formulation added to the mix.
Bagging of finished pellets should be done gently to avoid damage that can produce cracks or fines and lead to poor pellet water stability. Feed should be stored properly, indoors in a clean area and stacked correctly (Figures 23 and 24). Formulated feed
Shrimp feed production is an established and competitive industry (FAO, 2001a). This industry is well established in India and Viet Nam, and both countries have established feed standards for the feed for Penaeus monodon. These serve as good guidelines for formulated feeds in general. Commercial feed companies also provide the proximate analysis of their feeds (Table 5).
Least-cost feed formulation is combining many feed ingredients in a certain proportion to provide the target animal with a balanced nutritional feed at the least possible cost (Feedsoft Corp., 2009). When formulating a feed, many ingredient combinations will meet the nutrient requirements of the target species (Houser and Akiyama, 1997) (Table 13a).
Numerous least-cost computer software programs to formulate feeds are now commercially available and minimum (e.g. arginine) or maximum levels (e.g. fibre) of certain feed constituents are targeted (Table 12).
Methionine, lysine and arginine are usually the most limiting nutrients to least-cost optimization of commercial feed formulae (Fox et al., 2006). Tryptophan, isoleucine and threonine may also be deficient in feed ingredients (Houser and Akiyama, 1997). Knowledge of optimal feed formulation is necessary for all nutrients in addition to protein, to attain maximum nutrient retention by the shrimp (Beseres, Lawrence and Feller, 2005). Waste products (faeces) and uneaten feed are a significant source of inorganic and organic nutrients within shrimp ponds (Nunes and Parsons, 1998). Pond water quality and wastes affect pond production and shrimp disease and susceptibility (Tacon and Barg, 1998).
Feed prices
Shrimp feed prices by country clearly show that the feeds for P. vannamei are generally cheaper (Figure 25). Penaeus vannamei has generally lower nutritional needs, including protein levels.  Typical shrimp feed formulations
Various feed ingredients have been detailed above, as well as the nutrient requirements of P. indicus (Table 2a). Table 4 provides examples of feed formulations for P. indicus and Table 12 provides suggested feed ingredient inclusion levels. |
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