The Use of Proteins in Aquaculture Feeds

Feed protein is essential for all living organisms, but animal proteins are the most important protein sources for shrimp and fish feeds due to the amino acid profile. Fish and shrimp, like other species, respond best to protein sources of high biological value or in other words, those proteins with a good amino acid balance, primarily of essential amino acids. The best sources of proteins as far as biological value is concerned are animal proteins including fish meal, squid meal, shrimp head meal, oyster meal and mussel meal.

Among vegetable proteins for fish and shrimp feeds, soya has been reported to be the one with the best quality. Soya is typically used in one of three different forms: soya extracted without bran (49% protein), extracted soya with bran (44% protein) or full-fat soya (38% protein). Because soya is deficient in one essential amino acid (methionine), it is not used at high levels (10 to 20%) in shrimp diets. If we were to compensate for the methionine deficit with synthetic amino acid it would quickly dissolve in the pond water due to its solubility. Soya also tends to destabilize pellet agglutination making pellets less durable in the water.

Fish do not require a high percentage of methionine; and up to 30% soya or more is used in fish feed (tilapia and trout). However, as soya is very expensive in Ecuador it is only used when cost permits.We use full-fat soya meal in shrimp diets to improve the fatty acid profile because soya oil is rich in linoleic acid (18 C:2w6) and linolenic acid (18 C:3w3).

Of the high biological value protein sources for shrimp mentioned above, only fish meal and shrimp head meal are routinely available in Ecuador. Quality is a major problem when considering use of shrimp head meal. The raw material for shrimp head meal (the heads) comes from different packing companies and is not protected either physically (refrigerated) or with preservatives from exposure. Shrimp head meal arrives 40 to 50% decomposed or in the process of putrefaction and also contains high levels of sodium metabisulfite, the preservative used for shrimp export. For these reason, shrimp head meal cannot be routinely included in fish or shrimp diets.

As a result of the problems associated with shrimp head meal, the only dependable source of protein for shrimp feeds in Ecuador is fish meal. Fish meal quality varies with processing as well; and it is important to recognize differences in sources when including it in feeds. If the meal is made with fresh fish and then steam-dried, the result will be a fish meal with optimal quality and the highest nutritional value (Table 1). If the fish is fresh but dried under high temperature direct heat, large quantities of amino acids (mainly lysine) and vitamins are lost due to excessive heat.

In addition, histamine, a dangerous substance, is formed due to the degradation of the amino acid histidine. If the fish is dried under low temperatures, histamine percentage will be between 600 and 1,000 ppm. While this level will not cause major health problems for fish and shrimp, it will affect the availability of lysine thereby lowering shrimp performance. Histamine levels above 1,000 ppm affect crustacean health and indicate that histidine will be essentially destroyed.

If waste fish (offal remaining after fish are cleaned and filleted or after tuna or sardines have been canned) are processed, a lower protein (48–52%) but good quality fish meal will be obtained if it was steam-dried with slow direct heat. On the coast of Ecuador we use two low temperature dryers for this process.

All fish meal obtained from decomposed fish or in the process of putrefaction contains biogenic amines which are toxic substances derived from enzymatic amino acid degradation by the amino-decarboxylase action (Table 2). This catalyzes the transformation of amino acids to biogenic amines.

Fish meal degradation is easy to detect due to a characteristic odor of putrefaction; and the laboratory is able to confirm it through chromatographic techniques. This meal is not used in aquaculture feeds. Formulating shrimp and fish feeds

SHRIMP FEEDS AND REARING SYSTEMS

Nutritive value of the three types of fish meal used in Ecuador to formulate fish and shrimp rations is shown in Table 2. Steam-dried fish meal is not produced in Ecuador and must be imported from Peru or Chile. When we have steamdried fish meal available, priority is given to use in pre-starter diets or the first diet formulated for post-larvae sown directly into ponds. In addition we have formulated a special diet for the ‘remaining’ or slow-growing shrimp that will contain 60% of the high quality steam-dried fish meal.

The grow/finish formulation contains 25% crude protein. About 60 to 65% of this protein comes from fish meal processed at moderate temperatures with direct heat, while the remaining 35 to 40% comes from either soyabean meal or full fat soy. When good quality fish meal is in short supply we must use fish meal made from waste fish and cannery (tuna/sardine) waste.

Shrimp (P .vannamei) larvae are either sown directly into ponds or started in hatcheries. If larvae are direct-sown the initial diet contains 30 to 35% crude protein while formulas contain 40% crude protein if post-larvae are started in pre-hatcheries. The diet fed to direct-sown shrimp is given for 4 or 5 weeks until juveniles reach 2 to 3 g.

From this point on the grow/fattening diet is fed (25% crude protein) until harvest at 12 to 16 g body weight. Of the total protein in this diet about 60% is from fish meal and the remainder from vegetable sources. In addition to the fish meal, the completed diet will contain, soya, wheat, rice hulls and molasses. Nutrient requirements for the life stages of the shrimp are in Table 3.

Table 1. Analysis of ingredients used in shrimp and fish feeds.

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*HUFA = highly unsaturated fatty acids.

Table 2. Formation of biogenic amines by amino acid transformation in fish meal made from waste fish.

The Use of Proteins in Aquaculture Feeds - Image 2

The Use of Proteins in Aquaculture Feeds - Image 2

This ratio of animal to vegetable protein, 60:40, has given us the best results in terms of survival rate and feed conversion during the 16 years in which we have concentrated on aquaculture, especially shrimp, nutrition.

Shrimp is by far the most important sector of the Ecuador aquaculture industry with 99.5% of producers involved in shrimp culture. Of these producers, 95% rear shrimp in semi-intensive operations without artificial aeration. The remaining 5% use extensive rearing systems.

In the semi-intensive culture system there are two densities used. Postlarvae are either sown at 90,000 to 150,000 per hectare or 200,000 to 350,000 post-larvae per hectare. There are advantages and disadvantages to both systems, but with good management and balanced nutrition survival and feed conversion can be good in both systems.

Yields also vary with density and management. When post-larvae are sown at 90,000 to 150,000 per hectare, the initial diet contains 30% crude protein and is fed through the fourth or fifth week before starting the grow/fattening diet. With densities of 90,000 to 150,000 animals per hectare yields are in the range of 1,500 to 2,000 lb per hectare within a time frame of 14 weeks. Feed conversions are 1.4 to 1.7. The 14 week growing cycle allows us to have three cycles per year.

TILAPIA CULTURE AND FEEDING

Tilapia are also raised in Ecuador. In these diets animal and vegetable proteins are used in a 50:50 proportion. Depending on the cost of soya, a ratio of 40:60 animal/vegetable protein is used; however, as previously mentioned soya is very expensive in Ecuador.

Tilapia are fed three or four times daily. Tiapia fry (young fish 0.012 to 2 g) are fed a micro-pelleted feed. This feed, which is imported, is given for a 28 day period. Following this period, rearing stages and associated diet changes are as follows:

Table 3.Nutrients required by shrimp during different life stages (semi-intensive hatchery).

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Table 4. Nutrients required by tilapia during different life stages (semi-intensive hatchery).

The Use of Proteins in Aquaculture Feeds - Image 4

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1st Stage

This phase begins with fish weighing 2 g and continues through 15 g body weight. The formula used during this period contains 36% crude protein and is fedin meal or fine granular form (Table 4). The length of this part of the growth cycle is 60 days. Fish are grown in this phase at a density of 60 animals per square meter.

2nd Stage

The tilapia are placed in ponds at a density of seven animals per square meter. The feed is fed in extruded form (1/8 inch mesh) and contains 28% crude protein. This stage continues for 120 days until fish reach 200 g body weight.

3rd Stage

During this 60 to 90 day period fish are maintained at a density of only three animals per square meter. The extruded feed contains 24% crude protein. At the end of this period when the tilapia have reached 350 g body weight they are collected and placed in a polyculture system with shrimp.

Polyculture of shrimp and tilapia

The polyculture phase of rearing begins with tilapia weighing 350 g and shrimp weight 2 to 3 g. Fish are maintained at a density of 1.2 animals per square meter during this 100 day period. At harvest the tilapia weigh 550 to 600 g.

The tilapia diet contains 22% crude protein and is fed in extruded form (Table 4). The ingredients used in this formula are the same or similar to those used in the shrimp feeds: fish meal dried at moderate temperatures, soyabean meal (44% crude protein), wheat, wheat bran, rice bran and molasses.

The results as far as performance, survivability, and feed conversion for shrimp as well as tilapia have been very good as long as the techniques for managing the pond and balancing feed have been followed properly.

Author: GUILLERMO WEIR
Agroindustria Davipa S.A., Guayaquil, Ecuador

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