WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2018 29 Further refining this concept, multiple species of plants and animals can be grown in land-based contained systems where the plants that produce protein are fed to fish and shellfish and metabolites discharged by the animals fertilize the plants. Nutrients imported into the system can be protein-based pellets for fish or dissolved fertilizers for plants. Nutrients cycle back and forth between plants and animals. Metabolic products of one species become nutrient sources for others. Protein retention in the system then increases and a greater percentage of input nutrients are eventually exported from the system as valuable crops. IMTA is considerably more efficient than conventional aquaculture. A conventional single-animal aquaculture system with an assumed level of 20 percent protein retention releases 80 percent of the feed inputs to the environment. By contrast, an IMTA system with a hypothetical 40 percent protein retention wastes only 60 percent of the nutrients in feed. As a result, protein inputs to this new system produce twice as much animal protein as in conventional aquaculture systems. In short, IMTA yields much more protein with much less waste. Similarly, an IMTA system with 60 percent overall protein retention wastes only 40 percent of imported nutrients. For the same nutrient inputs as the conventional system, the IMTA system with 80 percent retention efficiency will further reduce waste. At this level of protein retention, a given amount of nutrient inputs into conventional aquaculture systems produces four times as much animal protein when used in an IMTA system. Figure 1 shows the relationship between nutrient waste and retention as retention increases. If IMTA systems can be designed to achieve 80 percent protein retention, the future global need for 4 billion t of grain protein can be reduced to 1 billion t of additional plant protein. This is a profound difference of global importance. Economic Impact If consumer prices of seafood are to approach other forms of animal protein such as beef, pork and poultry, total growing, processing and distribution costs for aquaculture products must be reduced. We cannot expect widespread consumption of aquaculture products at current consumer price levels that are uncompetitive with other animal protein sources. In most forms of fish production, feed accounts for over half the cost of production. If we can reduce overall feed costs in aquaculture production systems, we can reduce total costs of fish protein to consumers. For example, assuming that feed accounts for 75 percent of total farm-gate production costs in a conventional single species aquaculture system with 20 percent protein retention and assuming the total cost to grow fish is $0.91/kg, feed costs are $0.68/kg of fish. All other growing costs would be $0.23/kg. In contrast, with an IMTA system providing 80 percent protein retention, feed costs would decrease to $0.17/kg of fish produced and total costs would decline to $0.40/kg. This is a major cost reduction to a level close to costs of production for other animal proteins. Capital Required to Produce the Additional Amount of Fish In my recent book AQUACULTURE: Will it rise to its potential to feed the world ?” I roughly estimate the capital to build aquaculture facilities, with concomitant feed milling, processing and other infrastructure, requires an average of $4.50/kg of production capacity or $4,500/t. This capital cost may be higher or lower depending upon the species grown and facility location, but these capital costs are useful assumptions for this analysis. For the additional 400 million t more annual fish production required, approximately $1.8 trillion of new capital must be allocated to aquaculture over the next 30 years. This is admittedly a rough approximation. Over the next 30 years, this necessary investment will average $60 billion annually in new plant and equipment. Although this is a large amount of capital needed to build new facilities and related infrastructure, it is a small amount compared to the US total domestic investment in plant and equipment. In 2016 that figure was $1.6 trillion. This number is confined to the US economy. Much of the capital required for new aquaculture likely will be financed in foreign economies. While large, the amount of new capital should not be limiting. Aquaculture and the Poultry Revolution Aquaculture is following the path of broiler production in the US during the last half of the 20th century. In 1950, 12 to 15 weeks were required to grow a broiler chicken to market size. At the end of the century, it was reduced to five weeks. Broilers were formerly a highcost but are now a low-cost source of animal protein. The following four factors brought about this dramatic change: • Selective breeding for fast growth. • Contained environmentally controlled husbandry with the elimination of competing animals for feed from outside the culture system, along with elimination of disease vectors. If IMTA systems can be designed to achieve 80 percent protein retention, the future global need for 4 billion t of grain protein can be reduced to 1 billion t. For an IMTA system providing 80 percent protein retention, feed costs would decrease to $0.17/kg of fish produced and total costs would decline to $0.40/kg. This is a major cost reduction to a level close to costs of production for other animal proteins. (CONTINUED ON PAGE 30) Integrated Multi-Trophic Aquaculture Systems Retained protein vs wasted protein 0% 100% 10% 90% 20% 80% 30% 70% 40% 60% 50% 50% 60% 40% 70% 30% 80% 20% 90% 10% 100% 0% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Fig. 1 Percent protein retention in products Wasted to environment Protein retained Protein Retained FIGURE 1. Percent protein retention in products Integrated Multi-Trophic Aquaculture Systems — Retained protein vs wasted protein
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