Survey of the production, processing and nutritive value of catfish by-product meals in the Mekong Delta of Vietnam

Nguyen Thi Thuy, Nguyen Tan Loc, J E Lindberg^* and B Ogle^*

College of Agriculture and Applied Biology, CanTho University, CanTho City, Vietnam
nthithuycn@ctu.edu.vn
^*Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences,
PO Box 7024, S-750 07 Uppsala, Sweden

Abstract

A formal survey based on a semi-structured questionnaire was conducted among catfish farmers, and catfish and catfish by-product processing companies in five provinces (CanTho, An Giang, Dong Thap, Vinh Long and Tien Giang) in the Mekong Delta of Vietnam. Samples of meals were taken for analysis of chemical composition, including crude protein (CP), ether extract (EE), crude fibre (CF), ash, amino acids, fatty acids, and minerals.

The results show that most catfish farmers were changing to raising catfish in ponds and in the Dang Quang system, which is found along the Hau and Tien Rivers, while raising Tra catfish in floating cages was decreasing because of higher costs. The amount of catfish by-product produced in the Mekong Delta is around 710 tonnes/day, of which 53% is dried catfish meal for animal feed, 42% is wet fish meal for aquaculture, and around 5% is for human consumption. The catfish by-product meals were found to be high in fat (10-33% EE) and calcium (4-13%), while the CP content in head and bone by-product meals was rather low (35-42%). The broken meat and skin by-product meals had relatively high CP content (45-62%), a good balance of essential amino acids, and were high in lysine (5.45-9.33 % of DM).

Keywords: Catfish by-product, Dang Quang system, fish by-product meals, floating cage system, Mekong delta, Tra catfish

Introduction

The most important region in Vietnam for catfish farming is the Mekong Delta, where An Giang Province produces the greatest amount (VASEP 2005). Tra (Pangasius hypophthalmus) and Basa (Pangasius bocourti) catfish production has developed very rapidly in the Mekong Delta in recent years because of the high value of the exported products (Pham Van Khanh 2004). Cultivation systems using ponds, floating cages and the so-called Dang Quang system, which is common in slow-flowing rivers and involves using nets to enclose an area under the water surface, are dominant along the Hau River. Catfish farming is a traditional occupation in the Mekong Delta, and today many workers earn their living in the processing and export businesses. A number of large factories produce aquaculture products for export, such as Pangasius fillet, and as a result there are large quantities of by-products available, that are processed to give raw catfish meal (Le Thi Men et al 2004). This is a valuable protein source for livestock, especially pigs.

Several factories collect the raw catfish by-products from the export processing factories and produce both dry and wet fish meal, which is sold as feed for the livestock and aquaculture industries. It is important to know how the different processing techniques for producing catfish by-product meals affect their chemical composition, for example the crude protein, amino acid and fatty acid contents, in order to determine which are the most appropriate for inclusion in pig diets in terms of growth performance, meat quality and economics.
 

Materials and methods

The survey was carried out from September to November 2005 in five provinces in the Mekong Delta (Cantho, An Giang, Dong Thap, Vinh Long and Tien Giang) where the Tra catfish production and export processing companies are concentrated. The survey focused on catfish raising systems, export processing companies and catfish by-product meal processing factories. In total senior officials at ten companies were interviewed using a semi-structured questionnaire, to determine the main problems and potentials for catfish raising and catfish by-product meal production. The information collected included:

• Catfish cultivation systems and kinds of catfish raised, in order to identify the importance of raising fish for export relative to other activities.
• Details of the processing factories in each of the five provinces.
• The different kinds and qualities of catfish meals that are produced in each factory, and drying and processing details.
• The main problems that the by-product processing factories and catfish farmers are experiencing.

Chemical analyses

Samples of by-product meals from each processing factory in the different provinces were analyzed for DM, CP (Kjeldahl N x 6.25), ether extract (EE), nitrogen free extract (NFE), ash, calcium and phosphorus by standard AOAC methods (AOAC 1990). Also fish meal samples were analyzed for amino acid (Spackman et al 1958) and fatty acid composition by gas chromatography (GC/FID- ISO/CD 5509:94).

Results and discussion

Catfish cultivation systems

Due to the high value of catfish fillet internationally, production has developed rapidly in recent years and as a result catfish aquaculture, especially of Tra catfish is developing very rapidly in An Giang, Dong Thap and Cantho provinces. There are three systems for raising catfish in the Mekong Delta: pond, floating cages and the Dang Quang system. Access to water, ecological conditions and economic factors are the main determinants of producer decisions as to which system to use. In recent years, when the price of catfish was high (12 000 -14 000 VND/kg), the floating cage system was very popular, although raising catfish in floating cages gives lower benefits than the other systems because of higher input costs, and also the lower fillet proportions (32-33%), due to higher abdominal fat (17-25%), result in lower prices. This is probably a result of the higher fish density (100-120 fish/m³), and thus reduced fish movement in floating cages. According to the producers typical densities for the Dang Quang and pond systems are much lower, at 50-70 fish/m² and 30-50 fish/m² water surface respectively. Currently, the pond and Dang Quang systems are more popular for raising Tra catfish than floating cages, and the pond system is increasing most rapidly in Can Tho and An Giang provinces.

In 2005 the prices of catfish in Vietnam decreased to 9 000 - 10 500 VND/kg, so farmers who used floating cages lost income. Moreover, the uncontrolled raising of Tra catfish leads to increased pollution of water sources, and a higher incidence of morbidity and mortality, and as a result producers are compelled to use chemicals and antibiotics for treatment. Many antibiotics for the control of catfish diseases contain Malachite green, so it is impossible for the producers to export the fish. According to a survey published by the Ministry of Agriculture and Rural Development in 2005 about 75% of producers using Tra floating cages in the Mekong Delta lost income (Nguyen Chinh 2005). Consequently most have given up raising Tra catfish, and now raise other species of freshwater fish such as Black catfish, Pink tilapia, Snake head and White birdfish. These species are suitable and profitable for rearing in floating cages for domestic consumption, while the other two systems are still profitable for raising Tra catfish for export.

Many producers have converted poor agricultural land to intensive ponds for raising fish for export. The pond system has a number of advantages and benefits compared to the other systems. Firstly, producers can control the water environment, which has considerable effects on performance, mortality and meat quality. Secondly, when diseases occur, producers can control them by using medicines more effectively and by changing the water every day. In addition, the loss of feed by water flowing through floating cages is eliminated, and the proportion of meat fillet of pond Tra fish (33-36%), and thus the price, is higher than in fish from the other systems, because of lower abdominal fat as a result of lower fish density and increased movement.

Dang Quang is a system that producers use along the Hau and Tien rivers. Inox nets are used to enclose an area under the water surface and are connected to bamboo on the water surface. Dang Quang are located in rivers which have slow water flow. Catfish reared in the Dang Quang system have better performance and meat quality (pale colour) and, according to the export processing companies, have a higher proportion of fillet (33-36%) than those reared in floating cages (32-33%), so producers can sell them at a higher price. In addition, it is less expensive to remove the muddy material on the bottom than using a pump to change the water every day, as is necessary in the pond system.

Catfish production and by-products

In Vietnam, there are10 major export processing companies that directly export their products, and many smaller companies indirectly involved in Tra and Basa catfish production, almost all located in the Mekong Delta. These products are exported to 33 countries around the world, and catfish fillet is the most important aquaculture export after shrimp. The results in Table 1 show the water surface area for raising Tra catfish in 2005.

Production in An Giang Province occupied the largest area, followed by Can Tho Province, with lower production in Dong Thap, Vinh Long and Tien Giang provinces. According to the Vietnam Association of Seafood Exporters and Producers (VASEP 2005), in October 2005 between 1,200 and 1,400 tonnes/day of Tra catfish were collected from farmers in the Mekong Delta for processing for export.

Around 195, 250, 130, 65 and 58 tonnes of by-product per day are produced in Can Tho, An Giang, Dong Thap, Vinh Long and Tien Giang provinces, respectively. Most of the by-products from the export processing companies are transferred to fish meal processing factories as an input material. There are several different classes of by-product: Livers, stomachs and swimming bladders are sold to restaurants, while head and bone, skin and meat scraps, produced in either wet or dry form, are for animal and aquaculture feed. They are produced either mixed or separated into skin and broken meat and head and bone by-product, depending on the output contract of the fishmeal factories, as they differ in chemical composition and price. Small amounts of by-product, for example skin and broken meat, are bought by fish farmers who grind them and mix with fresh broken sea fish to make aquaculture feed.

By-product processing methods

There are several different methods for producing fish meal from Tra fish by-product. However, in general, the basic process in most of the methods involves separating the fat out of the product, which requires considerable investments in equipment. Cantho Province has the largest number of dry fish meal factories, while numbers are slowly decreasing in An Giang and the other provinces in the Mekong Delta. The main constraint is that the price of the meal and oil is fluctuating and sometimes is lower than the costs of production. As Tra fish meal has a high fat content, the quality deteriorates when stored for a long time, which is sometimes done in anticipation of increasing prices. Many of the by-product meal companies in An Giang Province are changing to producing wet fish meal for the aquaculture industry, both for Tra, Basa and other freshwater fish, because of the higher benefits compared to producing dry fish meal. Wet fish meal is produced by grinding, cooking the fresh by-product and mixing with cassava root meal, and is used immediately as feed for aquaculture.

The processing of catfish by-product is only a little different between provinces. Firstly, the by-products are finely ground, cooked and then separated into three fractions (Figure1).

Oil floats on the surface and is removed by bucket and further refined before being transported to storage tanks. The middle level is liquor (waste water) which is high in protein, and also is a cause of environmental pollution, because of the unpleasant odours that develop after being stored for some days. Sometime it is used together with sea fish to produce fish sauce for human consumption. In An Giang and Dong Thap provinces cassava root meal is added to the waste water and sold as condensed fish meal to fish producers, either as wet feed or after sun-drying or drying by machine to produce dry fish meal for animal feed (Can Tho). The lowest fraction is waste material, which is used to produce fish meal, after being pressed and dried by machine (Can Tho), sun-dried (An Giang) or dried on trays (Dong Thap). The final step is dry grinding with an antioxidant substance added. Drying by machine is most popular in most provinces, as it is less labour intensive than drying by tray, and sun-drying is only applied in some small-scale factories. However, fish meals that are produced by the different drying methods do not differ substantially in quality.

In general, there are 3 kinds of Tra fish meal produced, the best quality being catfish meat meal (Group 2), which is produced from separated broken meat. However, this is only a small proportion of the total amount. The most common meal product is head and bone meal (Group1), which has the lowest protein content, and the meal from waste water production (Group 3).

Problems of catfish by-product meal producers

In order to separate out the fat in the by-product, the processors have to invest considerable amounts for equipment and labor, but cannot determine the price of their product, which depends on the markets. Consequently, many producers lose money when the sea fish meal and oil product prices decrease. In addition, environmental pollution is also an important problem for catfish by-product producers, because processing results is considerable volumes of waste water, which give off unpleasant odours. It would be preferable if the producers of the catfish by-product meal could improve or change the processing techniques to reduce the release of waste to the environment. An alternative solution could be to ensile the by-products with cereal by-products, such as rice bran, for subsequent use as animal feed, or to feed the waste water directly to pigs.

Chemical composition of catfish by-product meals

The data in Table 2 and 3 show the chemical composition of the three categories of catfish by-product meal.

These are Group 1 (head and bone by-product meal) in which the crude protein is lower in comparison with that from Group 2 (broken meat meal). The boiling and drying methods in this process do not affect the protein content in the meal, which is confirmed by the study of Bui Xuan Men (2005). The ether extract in fresh by-product (10-21%) was higher than that in catfish meal because of the greater efficiency of fat removed in the process. Catfish by-product meal is high in fat compared with other fish meals, which means that it is quickly oxidized and destroyed during storage. However, it is high in minerals such as calcium and phosphorus, which are required by breeding animals such as the sow and laying hen. Calcium and phosphorus ranged from 7-13 % and 2-3% respectively.

Broken meat and skin by-product meals (Group 2) are high in crude protein (Table 3), the content depending on the amount of skin added to broken meat, with protein content decreasing in proportion to the skin added.

The ether extract in meat by-product and skin is higher than in head and bone by-product meal, although the mineral content is lower. Broken meat and skin by-product meal is considered to be a higher quality meal compared with sea fish meals, and animal feed companies generally use this product in commercial feed for exotic animal breeds.

The fish meals in Group 3 (Table 3) include waste water, with or without waste matter from the boiling process, and condensed by adding cassava waste powder. Normally this product is sold directly to the aquaculture producers, particularly in An Giang province where aquaculture is developing rapidly. Another fraction is ground dried to give dry fish meal which is either low (about 13% CP without waste matter) or quite high (26-27% CP with waste matter) in crude protein. It is also high in NFE, although ether extract is rather low. This product is generally used in commercial feeds for local breeds of pig and poultry.

Amino acid content of catfish by -product meals

The nutritive value of any protein is directly related to the amino acid composition of that protein. A protein that does not contain the proper amount of amino acids will be imbalanced. Group 2 catfish by-product meal contains an excellent balance of essential amino acids, especially with respect to lysine and methionine (Table 4) and is considered to have a high nutritive value for livestock. However, in head, bone and waste water by-product meal the amino acid composition is less well balanced.

Fatty acid content of catfish by-product meals

The oil content in catfish by-product meal is generally high (Table 5), as this is a specific characteristic of catfish.

In general, the fatty acids (Table 6) in the different groups are not different in their total content of saturated fatty acids, such as lauric, myristic, palmitic and stearic acids, and mono- and poly-unsaturated fatty acids, such as oleic, linoleic and linolenic acids.

Conclusions

• The pond and Dang Quang systems for raising catfish are developing rapidly in the Mekong Delta, while many producers that previously used floating cages now raise other species of freshwater fish instead of Tra catfish.
  
  
• Catfish processing by-products are abundant and are estimated to make up about 65 % of the total raw catfish material.
  
  
• Most of the by-products are used to produce fish meal, used locally for livestock and aquaculture feeds.
  
  
• There are only small nutritional effects of the different fish meal processing techniques on the nutritive value, and any differences in nutrient content depend mainly on the by-product input material.

Acknowledgements

The authors would like to thank Sida/SAREC for financial support of the study, and also the Department of Animal Husbandry, Faculty of Agriculture, Cantho University, for use of laboratory facilities. We are also grateful to the offices of agriculture and aquaculture of the five provinces surveyed for providing the statistical data.

References

AOAC 1990 Official Methods of Analysis 15th edition. Association of Official Analytical Chemists. Washington, DC. Volume 1: 69-90.

Bui Xuan Men 2005 Effect of processed catfish by-product use as protein supplements in diets of growing ducks. Proceeding of the Workshop on the Technology Development for Livestock Production. February 22, 2005. JIRCAS-CTU, 91-97

Le Thi Men, Preston T R, Truong Van Hieu, Duong Thuy Ngan and Huynh Thu Loan 2004 Evaluation of Tra catfish (Pangasius hypophthalmus) residue meal to replace fishmeal in diets for fattening pigs in the Mekong Delta of Vietnam. http://www.mekarn.org/proctu/lemen37.htm

Nguyen Chinh 2005 Evaluation of use of medicines and biochemicals in extensive catfish raising in An Giang and Cantho Provinces. MSc Thesis, Cantho University.

Pham Van Khanh 2004 Techniques for raising Tra and Basa Catfish in floating cages. Institute of Research on Aquaculture. Agriculture Publishing House, Ho Chi Minh City, Vietnam (in Vietnamese).

Spackman D H, Stein W H and Moore S 1958 Automatic recording apparatus for use in chromatography of amino acids. Analytical Chemistry.30:1190-1206.

VASEP 2005 Vietnam Association of Seafood Exporters and Producers, Weekly Aquaculture Trade Journal, October 7, 2005.

Received 13 June 2007; Accepted 12 July 2007; Published 4 September 2007

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