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Ultimately it will be economically and socially imperative to improve the energy efficiency of all aspects of the food-supply chain. However, it is possible that greater overall gains in energy savings can be made by improving the efficiencies of processing, transport, retailing, and even household storage and preparation than can be made by improving energy efficiency in the production sector. This may have particular relevance to aquaculture, where important products are produced only in certain regions (marine shrimp in the tropics; salmon in the north-temperate) and are stored and shipped long distances for consumption.

Water used for water exchange is pumped from bays or estuaries and discharged back into the same water body, so only water lost to evaporation and seepage is used consumptively. More important than water use alone, however, water exchange generates large volumes of waste, increases the risk of pathogen transfer to and from the outside environment, and increases production costs associated with pumping. 3 in Chapter 7). Total water use in channel catfish farming (as an example of pond aquaculture in general) varies greatly depending on water source and phase of culture (see Chapter 6).

5). Extensive land use is the result of the pond functioning as both an animal confinement area as well as a waste treatment facility. For example, more than 95% of the total area of a catfish pond functionally acts as a photosynthetic waste-treatment lagoon and less than 5% of the total area serves as a “fish-holding” area (Brune et al. 2003). In effect, more than 95% of the Fig. 5. Pond aquaculture requires considerable land area because support functions such as waste treatment and, in some systems, food production are inherent in the ecosystem rather than being appropriated from ecosystems outside the culture system.