Aquaculture and the potential for aquafeed

by Teresa Acklin
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Aquafeeds are fast becoming a significant portion of the global feed market for the 21st century.

By Samuel P. Meyers

   Aquaculture of both marine and freshwater fish and crustaceans is one of the fastest growing food production systems in the world. Along with these developments have been significant increases in the past several years in numbers of commercial organizations engaged in aquacul-turally-related products and services, especially in production of aqua-feeds.

   Aquafeed manufacturers are experiencing a variety of developments, including introduction of new concepts such as pellet stability and palatability, as well as the designation “environmental certified feeds,” which results in decreased damage to the culture system. Accelerated usage demands on fishmeal, together with decreasing catches in world fisheries, have resulted in significant increases in use of various alternate protein ingredients for aquafeeds.

   By the turn of the century, it is projected that as much as 25% of available fishmeal will be utilized in aquaculture. Physical characteristics of aquafeeds such as hardness, density and fat absorption are of increasing significance in terms of ingredients and processing methods, such as pelleting versus extrusion technology. Various plant and animal feed ingredients are being evaluated in terms of their nutritional properties for aquatic species.

   Information is increasing on dietary formulation requirements of particular “target” species along with relevant data on nutritional needs. Quality characteristics of aquaculturally-raised animals attributed to aquafeeds, notably critical sensory properties, are of significant importance, compared to those typical of wild specimens. Examples are noted of the status of specific commercially-raised fishes and crustaceans, along with projections of global aquaculture growth within this and the early part of the next century.

   Development and production of aquafeeds is now one of the fastest growing segments of the global feed market. This closely parallels the significant expansion of aquaculture and projections for growth in the rapidly approaching 21st century. Expansion in aquaculture and economically sound culture of existing and new species depends upon availability and use of superior feeds based on sound nutritional information.

   Aquafeeds represent the highest cost input in the aquaculture operation, one that ultimately dictates the final economic success of the venture. Similarly, ingredient quality itself is a major factor in formulation of superior aquafeeds. Characteristics of the aquafeed will affect all aspects of aquatic animal culture, as well as reflect the overall final consumer acceptance of the quality of the harvested product. Numerous articles, especially reports from the Food and Agriculture Organization of the United Nations, have repeatedly documented the production and economic status of the aquaculture industry and that of particular species, such as salmonids and crustaceans. Marine shrimp culture has exhibited truly spectacular growth over the past two decades, especially in Southeast Asia.

   Aquaculture production figures in 1994 from the F.A.O. report 25.5 million tonnes, comprising over 21% of the total world fisheries landings. This production represents an average annual growth rate of 9.4% per year since 1984 compared with 1.7% per year for capture fisheries.

   A recent F.A.O. report, Global Trends in Aquaculture and Aquafeed Production, accurately documents this growth. In Europe, aquaculture of seabream and seabass has shown significant development since the mid-1980s, as evidenced by production in Greece, increasing from 300 tonnes in 1988 to more than 12,000 tonnes in 1994. Total seabass/seabream production in the Mediterranean since 1990 has shown a five-fold increase to 28,600 tonnes in 1994. Numerous other examples of successful aquaculture ventures are variously cited in the literature of this global industry.

   Rapid growth in aquaculture can be related in part to a gradual decline in natural fisheries stocks, many of which have reached, or have far exceeded, their maximum sustainable yield. Various authorities suggest that any further increases in fishery production will depend upon acceleration of aquaculture efforts. An excellent example can be cited with various salmonid species, especially Atlantic salmon, where aquaculture output now exceeds 50% of the wild harvest.

   Current economic analyses of the global aquaculture industry have indicated a value of U.S.$50 billion and growing, while recent reports note as many as 1,257 companies currently are involved with aquaculture. The number of commercial fish farms is projected to increase significantly by the turn of the century. It is estimated that more than 300 species of fish are cultured worldwide, each with its own feeding habits and nutritional requirements.

   Here the concept and role of floating versus sinking feeds assumes considerable importance, as does the effect of particular ingredients. At the Seventh International Symposium on Nutrition and Feeding of Fish held in Texas, U.S., in 1996, Mr. Sunderland of the Wenger Technical Center presented data showing the significant effect of minor ingredients of feeds on physical characteristics of sinking extruded pellets.

      Factors Affecting Aquafeeds.

   Fish farms use an estimated 4.3 million tonnes of aquafeed valued at more than U.S.$2 billion. By 2000, the volume of aquafeeds is projected to grow to more than 14 million tonnes.

   In selection of a diet for aquaculturally-raised fish, factors such as aquafeed cost and market value of the fish, as well as overall diet performance (measured as FCR), are critical. Results suggest that FCR is more significant than actual price of the diet in evaluating total profitability of the fish farming operation. A major factor is feed energy level supplied, which is evident in comparisons of pelletized versus extruded diets, expressed as feed digestibility. Furthermore, the feed conversion ratio strongly depends on optimization of the feeding procedure or schedule.

   A variety of minor ingredients is becoming more available for aquafeeds. In addition to the carotenoid astaxanthin and dry de-oiled soy lecithin, other such ingredients include stabilized ascorbic acid, various pellet binders, as well as feeding attractants and palatability additives. At the April 1997 meeting of the World Aquaculture Society in Seattle, Washington, U.S., the subject of immunostimulants received considerable attention. Commercial yeast gluten products are now available to reduce stress-related factors related to disease outbreaks and increased animal mortality.

   An example of the effect of a specific feedstuff on aquaculture products quality can be seen in the catfish culture industry where excessive levels of dietary xanthophyll-containing maize gluten and alfalfa meal can produce an undesirable yellow color in the processed fillet.

   Information is rapidly accumulating on beneficial aspects of particular ingredients in aquafeeds. The carotenoid astaxanthin, used as a pigmenting agent in salmonid feeds, is now recognized as functional in early stages of fish development as well as in the enhancement of maturation and reproduction rates. Certainly, the role of astaxanthin as a strong antioxidant is well recognized.

   The value of lecithin as a source of essential phospholipids, along with its role in digestion and enhancement of dietary lipid absorption in aquafeeds, has been demonstrated. Other features such as improvement of physical properties, i.e., reduction of water-soluble nutrient leaching, are of no less importance.

   Numerous considerations affect use of a particular ingredient used in a commercial aquafeed. Along with availability and price are such factors as protein quality, energy digestibility, amino acid balance and presence of anti-nutritional factors. Again, the final palatability of the aquafeed assumes great importance. A properly designed, nutritionally adequate aquafeed may give inadequate performance if it is poorly accepted by the particular fish.

   In addition to the importance of nutrient content on aquafeed quality, the significance of physical characteristics of the pellet is recognized, especially its water stability and acceptability by the fish. This latter, often referred to as palatability, is a consideration of great importance when the diet may lack sufficient feeding stimulation properties.

   Apart from aquafeeds, it has been shown in swine pre-starter and starter feeds that palatability enhancers can increase consumption and utilization of high quality feeds. Palatability-enhanced feeds showed a 6% gain compared to the control pigs. Extra feed costs can be readily justified in such diets as well as in starter aquafeeds in terms of early rapid growth. Especially important in aquaculture is the enhancement of young animal survival, often by carefully formulated starter diets.

   Significant differences can be seen in aquaculture production by feeding habit and actual dietary fishmeal consumption. Nearly 90% of such production is by omnivorous and herbivorous fish, while in contrast, more than 90% of fishmeal consumption is in diets for carnivorous species, such as salmonids.

   In contrast to the culture of herbivorous/omnivorous food fish species, more than 66% of total finfish production within developed countries is based on culture of higher value carnivorous finfish species, including salmonids. At present, production of commercial aquafeeds for salmonids, representing 27% of total global compound aquafeed production, is totally dependent upon use of fishmeal and fish oil as the main source of dietary protein and lipid.

   In 1994, salmonids were the largest aquafeed consumers of fishmeal, representing as much as 49% of the total. Numerous articles have expressed concern regarding future availability of high quality fishmeal, notably in diets for carnivorous species such as salmonids. As much as 40% to 50% fishmeal may be included in the formulation, comprising the major cost factor in such diets.

   Estimated breakdown costs of a commercial Atlantic salmon extruded dry grower diet reveal protein sources account for approximately 67% of total costs. Most of this can be attributed to dietary fishmeal concentrations of approximately 50%. With such species, where proper pigmentation is critical, incorporation of dietary carotenoid astaxanthin alone represents as much as 13% or more of total cost. Use of alternative, more sustainable sources of dietary protein and lipid in aquafeeds is becoming more and more critical.

      Alternate Protein Sources And High-Energy Aquafeeds.

   Use of alternative protein sources is a major issue in aquafeed formulation, replacing complete dependency on fishmeal. With level production of fishmeal in the foreseeable future, growth in aquaculture will make increased demands upon this valuable marine protein resource.

   With increasing demands being placed on fishmeal usage and decreasing catches in world fisheries, we can expect to see a significant rise in use of alternate protein sources by the turn of the century. Soybean meal has been extensively examined as an aquafeed ingredient to reduce fishmeal usage.

   Other protein sources, including fisheries processing by-products and marine meal other than fishmeal, have been proposed. It must be emphasized that various problems exist with use of specific ingredients, including those of nutrition as well as palatability.

   A variety of such sources has been evaluated as partial or complete fishmeal replacers in aquafeeds. Most common among these is soybean meal. Examples of others include meat/bone meal, rapeseed (canola) meal, cereal by-product meal, and single-cell and miscellaneous plant proteins.

   With attention being given to improved fisheries resource utilization, various marine by-products/hydrolysates are also being examined as animal protein sources. The latter have notable value as feeding enhancers, especially when used in conjunction with plant or oilseed protein sources. It must be stressed that some of these alternate proteins may have negative qualities, such as fiber/ash levels, variable digestibility coefficients, along with cost and availability.

   With increased use of vegetable protein feedstuffs, attention must be given to inactivation or destruction of any anti-nutrients present as well as efforts to improve nutrient availability and digestibility. Various research has focused on use of dietary enzymes to impart greater nutrient digestibility/availability to the aquafeed. Again, the importance of feeding stimulants cannot be over-emphasized as a means to improve feed palatability and intake.

   In the United States, more than 90% of aquafeeds in the catfish culture industry are extruded. Such floating feed may be used as a “management tool” to monitor feeding activities in the ponds, especially when practices of feeding to satiation are employed. Even in pelletizing operations, use of expanders and modification of the mill conditioning chamber are becoming common practice to impart desirable features of the extrusion process, notably stability, to the pellet. Numerous studies point to the advantages of extrusion approaches compared to pelletizing of feeds, notably expressed in increased digestibility as well as durability of the feed particles. Certainly, the role of steam as seen in extruders and the use of expanders are well recognized in proper manufacture of optimal aquafeeds.

   Diets containing high levels of fat are now being used for various aquaculture fish species. Advantages include those of improved feed conversion with resultant lower feed costs as well as overall reduction in pollution load on the culture environment. In development of such aquafeeds, it is necessary to take into consideration the effect of fat concentration on the final pellet quality, notably its durability in the pond system.

   Studies on aquaculturally-raised catfish indicate that both source and level of dietary fat affect body composition and storage quality. Other work also has demonstrated that the fish tissue fatty acid profile reflects the type of lipid present in the diet. Recent studies with white sturgeon have demonstrated that feeding of dietary fish lipids increases the level of (n-3) polyunsaturated and highly unsaturated fatty acids in sturgeon muscles.

   The type of binder used affects fat absorption properties and the hardness of extruded fish feed. Similarly, fat concentration as well as the particular ingredients used influence final pellet quality. To increase the fat content, spraying fat on the pellets after extrusion is a common practice. Floating pellets can absorb about 30% liquid fat sprayed on after extrusion, compared with 15% for sinking pellets. Source and temperature of the fat also will influence the expansion properties.

      Environmental Considerations And Product Quality.

   Aquafeed manufacture has seen introduction of the concept called environmental certified highly digestible feeds. Such aquafeeds, also referred to as “low-pollution” feeds, serve to minimize buildup of deleterious organic and inorganic compounds within the culture system.

   Water pollution generated from aquaculture areas is becoming more and more of an international concern. Nutrients leaching from feed and undigested feed in the excreta of fish can adversely affect dissolved oxygen levels in the culture system. This has resulted in legislation in various countries requiring fish production operations to use highly digestible low-waste feeds with ecologically sound conversion ratios.

   The level of dissolved oxygen in the aquaculture environment is among the most critical factors in water quality. Less than optimal dissolved oxygen levels can stress the cultured animal leading to decreased food consumption and growth, along with increased susceptibility to disease and subsequent mortalities. Such susceptibility will vary with different fish species, depending on the length of the exposure period.

   Studies have shown that farm-raised fish can vary in color, texture, flavor and quality from free-living (wild) fish. Differences in the significant aspect of flavor can be because of diet composition, native differences in the enzyme lipoxygenase activity and the impact of the environment. Rapid uptake of off-flavor may occur in farm-raised fish such as catfish, leading to an undesirable marketed product. Addition of dietary ingredients such as tocopheral and astaxanthin to the feed have been shown to improve both color and oxidative stability of such aquaculturally-raised species as salmon and trout.

   Final quality of the aquaculturally-raised fish or crustacean is receiving increased attention, notably sensory properties compared to those of the wild specimen. Feed and feed management practices are being adapted to produce an aquaculture crop of superior quality and enhanced market acceptability. An excellent example is that of salmonid diets where astaxanthin carotenoid supplementation is needed to insure proper flesh coloration.

   Work has also shown a correlation between dietary fat level and composition and fat composition of the farmed fish. Diet especially influences the amount of nutritionally important fatty acids in the muscle of aquaculturally-raised fish. Furthermore, before a dietary ingredient can be effectively used in a least-cost formulation, the effect of the ingredient on color/flavor of the fish must be evaluated under production conditions.

   Critical product quality can be readily affected by the aquafeed itself as well as conditions within the culture system. Product aspects include such factors as flavor, texture, color and appearance. A major attribute of aquaculturally-raised animals is that of selective harvesting controlling quality and size of products, with selective harvesting for specific markets.

   Apart from the effect of feed quality on fish growth and feed efficiency, body size uniformity, reproduction, resistance to stress and disease and mortality also are affected. Nutritional and other consumer quality attributes of the fish are further considerations.

      Future Growth Of Aquafeeds.

   Current trends in development of aquafeeds portend significant growth in the rapidly expanding global aquaculture industry. Much of this can be related to improved formulations, resulting in superior physical and nutritional feed properties.

   Clearly, less polluting formulations will be mandatory as emphasis is placed on realistic sustainable aquaculture practices. As more intensified culture systems are developed, greater emphasis will be placed on critical optimization of the properties of the aquafeed, all of which contribute to a more economically sound feed conversion ratio.

   In addition to improved aquafeed formulations and the need for nutritional information on a variety of aquatic species, a major factor in acceleration of aquaculture is that of improved farm management practices along with controlled intensification of the culture system. Feeding options are directly correlated with intensification of the aquaculture process.

   With such intensification, a variety of farm management practices and feeding strategies becomes increasingly critical. Among such considerations are waste output, disease susceptibility and attention to environmental sustainability. Currently, we are seeing decreased growing time and increased harvests per year with various aquatic animals, much of which can be attributed to more efficient use of the particular aquafeed.

   A recent report on catfish farming in the U.S. state of Mississippi notes that a feed containing 24% to 26% protein (down from the 32% protein considered as the standard protein content for catfish feed) was sufficient for fish fed to satiation. It was emphasized that a properly designed feeding schedule was essential to obtain maximal performance of the catfish.

   We can anticipate increased attention being given to cultivation of omnivorous/herbivorous species that have lower dietary protein requirements and can thus be fed on lower-cost and more sustainable plant-based protein/lipid sources. Examples are seen in various species, such as channel catfish (in the U.S.) and tilapia.

   Tilapia is now the fourth largest cultured species group with an annual production rate of 12.8% since 1984, second only to penaeid shrimp. Tilapia has been described as “aquatic chicken,” adaptable to a variety of cultivation practices. Its white-fleshed and mild-tasting sensory properties, along with its marketing appeal as a boneless portion-controlled fillet, has added to the economic success of tilapia farming.

   As the farming system progresses from extensive to intensive, production increases per unit area, water exchange requirements increase, and ultimately, there will be a need for aeration and more complete feeds. Thus, while production per unit area increases with intensification, this must be carefully weighed against greater demands on resources and the critical need for careful management practices.

   In all likelihood, the key to future aquaculture success will depend upon establishment of sustainable production operations with attention to natural ecological factors along with recognition of resource availability and diverse human factors. Clearly, overall efficiency of resource use will ultimately establish the economic and ecological viability of the aquaculture operation. Proper aquafeeds unquestionably will play a major role in the attainment of successful goals in aquaculture.

   This article was prepared by Samuel Meyers for the 3rd East/West Industry Conference sponsored by VICTAM International and the International Feed Industry Federation. Mr. Meyers is professor emeritus, Departments of Food Science, Oceanography and Coastal Sciences, at Louisiana State University, Baton Rouge, Louisiana, U.S. His research has involved extensive studies of value-added seafood product development along with investigations of basic and applied global aquaculture practices, including fish and crustacean nutrition and appropriate aquatic feed development. He has traveled internationally in his aquaculture work, including service as a consultant in aquaculture nutrition for the Food and Agricultural Organization for the United Nations.