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Overview of aquaculture feeds

Global impacts of ingredient use

C.E. Boyd     Auburn University, Auburn, AL, USA

Abstract

Feed-based aquaculture is an important part of global aquaculture production. Feed use in aquaculture is expected to increase as aquaculture production expands to meet the demands of the growing human population. Aquaculture feeds require fish meal and oil made from pelagic, marine fish and products from agriculture as ingredients. The major concern related to ingredients is the large amount of fish meal and oil used. Aquaculture feed production also requires land and water for producing ingredients, uses energy, and emits carbon dioxide. Water pollution from feed-based aquaculture can negatively affect biodiversity. Impacts of aquaculture feed production and use can be reduced by finding substitutes for fish meal and oil, as well as employing feeding practices that maximize efficiency and minimize waste.

Keywords

Aquaculture and environment; Aquaculture effluents; Aquaculture feeds; Resource use for aquaculture feeds; Water quality

1.1. Introduction

The human population has increased drastically since 1950 (Figure 1.1), and the demand for food has increased accordingly. Agricultural production increased from about 3000 million metric tons in 1961 to nearly 7000 million metric tons in 2010-a rate of increase that is slightly greater than the population growth. This increase resulted mainly from intensification of agriculture, because land use by agriculture increased a mere 10%: from approximately 4500 million ha in 1961 to approximately 5000 million ha in 2010 (Boyd et al., 2013). Fisheries are an important segment of the global food system, presently representing approximately 20% of protein intake; as the population has grown, the demand for fisheries products has increased. This has resulted in overfishing, and global capture fisheries production has fluctuated annually but not shown a trend of increase since the mid-1980s (Figure 1.2). Most authorities feel that the ocean and inland waters have been fished to their sustainable limit, and capture fisheries production cannot be expected to increase in the future. The failure of capture fisheries production to increase as rapidly as population growth has not caused a scarcity of fisheries products, thanks to a dramatic increase in fisheries production through the farming of aquatic organisms or aquaculture (Figure 1.2). Aquaculture currently is the source of half of world fisheries production for human consumption and around 8-9% of the animal protein intake of humans (FAO, 2012). The human population is projected to increase from its current level of approximately 7200 million to more than 10000 million by the end of the century (Figure 1.1), with most of the increase occurring during the next 40 years. Aquaculture production must supply the entire future increase in demand for fisheries products because the capture fisheries are not expected to increase, and possibly may decline.
Figure 1.1 Historical and projected global population estimates.
Figure 1.2 Global fisheries production by capture and aquaculture. In the simplest form of animal aquaculture, shrimp, fish, or other aquatic animals are stocked into production units, where they eat naturally occurring food organisms (or the remains thereof). Natural productivity in such systems is low, and fertilizers (either organic waste/byproducts or commercial chemical fertilizers) are applied to increase food availability for culture animals. A much higher level of production can be achieved by applying high-quality, manufactured feed that culture animals can eat directly. The amount of feed and production may be increased if mechanical aeration is used to supplement natural sources of dissolved oxygen. To illustrate, penaeid shrimp yields in unfertilized ponds typically are 200-300 kg/ha. Yields of fertilized ponds may reach 400-800 kg/ha. Feeding alone can increase shrimp yield to 1500-2000 kg/ha before low dissolved-oxygen concentration becomes limiting. Yields often exceed 10,000 kg/ha in ponds with both feeding and mechanical aeration (Boyd and Tucker, 1998; Alday-Sanz, 2010). Land and water for aquaculture often are limited, and there is a growing tendency for intensification of production, as occurred in traditional agriculture. For example, yields of ictalurid catfish from farms in the southern United States were approximately 1500-1800 kg/ha in the 1960s, but they have steadily increased to an average of approximately 5000 kg/ha in 2012 (Hanson and Sites, 2012). This increase resulted from better feeds, higher feeding rates, and development of more efficient aeration systems (Boyd, 2012). According to FAO (2012), about two-thirds of aquaculture production systems received some feed input in 2012-up from about one-half of systems in 1980. In 2012, 34.4 million tons of aquaculture feeds were produced (Alltech, 2013). Although this amount is small compared to poultry feed (418 million tons), ruminant feed (253 million tons), and swine feed (218 million tons), aquaculture feed production is a large industry with considerable promise for future growth. Supplying goods and services for the growing human population requires tremendous amounts of resources and causes many negative environmental impacts. According to environmental nongovernmental organizations (eNGOs), the ecological footprint of humanity is 1.3-1.7 times greater than the world's capacity to supply resources and assimilate wastes (Boyd and McNevin, 2015). There is much concern about the sustainability of humankind-many feel that we are heading towards unprecedented ecological disaster. Aquaculture, like most other human endeavors, is finding it necessary to seek ways of lessening resource use and negative environmental impacts. The purpose of this chapter is to consider the global impacts of aquaculture feeds on resources and the environment.

1.2. Feed ingredients

Small fish, chopped trash fish, meat scraps, grains, plant meals, and even fish meal are sometimes used directly as aquaculture feeds. However, use of these materials as feeds has issues related to availability, nutritional quality, sanitation, etc. Manufactured feeds are designed according to the nutritional requirements of specific species. These feeds are compounded from a wide range of high-quality feedstuffs to include fish meal, squid meal, plant meals, crushed corn, wheat flour, rice flour, meat scrap meals, feather meal, bone meal, distillers dried solubles, fish oil, vegetable oil, vitamin packages, mineral supplements, antioxidants, etc. Typically, feeds are formed by controlling the size of the pellets to accommodate various species and growth stages for which they are intended. Representative feed ingredient recipes for some common aquaculture species are provided in Table 1.1. The representative feeds contain fish meal and plant meals, but the ratio of fish meal to plant meal varies considerably among species; it is greatest for salmon and trout, intermediate for shrimp, and lowest for tilapia and catfish. There is much effort to lower the inclusion rate of fish meal in aquaculture feeds, and some manufacturers offer feeds without any fish meal; for example, feeds for ictalurid catfish often contain no fish meal (Boyd et al., 2007). Fish meal-free feed typically contains a rendered meat product as a source of animal protein, but research has shown that some species can be successfully cultured with a feed containing only plant protein. The crude protein (nitrogen × 6.25) content of aquaculture feeds ranges from approximately 25% for certain herbivorous or omnivorous species to as much as 55% for some carnivorous species and early life stages. The average protein content for all feeds likely is around 35%. Lipid, in addition to that contained in other feed ingredients, is included in aquaculture feeds to provide energy and essential fatty acids; vegetable oil, fish or other marine oil, or a combination of both are the usual sources. Feeds for coldwater species such as salmon and trout generally contain a higher concentration of oil-especially fish oil-as compared to warmwater or tropical species such as channel catfish, tilapia, and marine shrimp (Table 1.1).

Table 1.1

Major ingredients and typical feed conversion ratios in feeds for some major aquaculture species

Soybean meal 14.0 15.0 24.5 38.3 34.5 Cottonseed meal - - - - 12.0 Corn meal 10.0 - - 48.8 20.4 Wheat...