28 JUNE 2015 • WORLD AQUACULTURE • WWW.WAS.ORG valued species such as shrimp, salmon, and certain marine fish (Boyd and McNevin 2015). The efficiency of fishmeal and fish oil use in aquaculture often is assessed by the fish-in:fish-out ratio (FIFO). This ratio (kg/ kg or t/t) is an estimate of the mass of live marine fish needed to make the amount of fish meal and oil required in the feed to produce a unit mass of the culture species (Boyd and McNevin 2015). The need to lessen fishmeal and fish oil use is widely recognized and the inclusion rate in feed has declined considerably in the past decade (Tacon and Metian 2008) but, because of the growth of aquaculture, the total use of fishmeal and fish oil is still increasing. The solution to the fishmeal and fish oil issue is to find replacements and much research is being done. Nevertheless, the FIFO ratio should be an indicator of the efficiency of aquaculture, because the amount of wild, pelagic forage fish that may be harvested from the ocean for making fishmeal and fish oil has a sustainable limit that possibly has already been reached or exceeded for most species. Small, pelagic forage fish are necessary as food for carnivorous species in capture fisheries and are used in making aquaculture feeds. In a sense, the two sources of aquatic food are in competition for the same resource. The carnivorous fishery demand is a natural demand that can only be affected by fisheries management while, on the other hand, the aquaculture demand is artificially imposed and can be manipulated through fishmeal and fish oil reduction in feed and use of replacements for those two ingredients. The FIFO often is adjusted for the inclusion of offal meal and oil but, even though a byproduct, offal meal and oil production is limited to the amount of marine fish processed. Although aquaculture certification standards may accept a FIFO of 1.0 for some species, full compliance with this standard would not remove fishmeal and fish oil as a potential bottleneck of production of certain aquaculture species in the future. Land Use Land use considers water surface area of ponds, support areas for ponds and other grow-out systems (embankments, canals, settling basins, roads, staging and parking areas, area for buildings, etc.) and the agriculture area used for production of plant ingredients in feed. The support area typically increases from nearly equal to the production surface area for small ponds (< 0.25 ha) to about one-fourth the production area for large ponds (> 4.0 ha). Land for feed ingredients usually range from 0.2 to 0.3 ha/t feed; the agricultural area for plant ingredients often exceeds the land area of aquaculture farms (Jescovitch 2014). Water Use Consumptive water use at the farmlevel is usually around 1,000 to 5,000 m3/t of production in freshwater ponds. Freshwater cage culture and flow-through systems retain only the amount of water included in harvested biomass. Brackishwater and marine aquaculture facilities technically do not consume water because saline water is not useful for domestic or agricultural uses (Boyd 2005). Nevertheless, energy is used to pump water at most aquaculture facilities and water discharge from production facilities may be polluted, lessening its value for other purposes. Thus, the collection of data on water use should include discharge volume. The amount of freshwater embodied in feed and other resources used in aquaculture should also be included. Pond volume plus the amount of water exchange is an estimator of both water use and effluent volume at a facility where ponds are drained at the end of each crop, the most common practice. Water use also should include embodied water used in producing plant feed ingredients, fishmeal in feed and fertilizers. The amount of water embodied in feed can be estimated by essentially the same procedure used for estimating land use for feed, using the water use for individual feedstuffs (Mekonnen and Hoekstra 2011) and fishmeal (FAO 1986). Typical values for embodied water range from 200 to 300 m3/t feed. Fertilizer contains relatively little embodied water − 9.4 m3/t nitrogen and 27 m3/t phosphorus. Although aquaculturists cannot control the use of embodied water — or other embodied resource use and impacts — resulting from feed use, they can reduce the quantities of embodied resources through better feed management to lessen feed use per unit production. Thus, embodied resources will be assessed to demonstrate the hidden benefits of good practices. Survival The percentage survival of the culture species should be calculated from the number of organisms stocked and the number of organisms harvested. These data will be available at certified farms. Most non-certified producers will have a fairly accurate knowledge of survival, but if not, it may be calculated from the number of organisms harvested divided by stocking rate. There usually is a close relationship between survival and production at harvest as illustrated in Figure 2 for a shrimp farm. Low survival in aquaculture systems usually is related to poor quality seed stock or improper acclimation and handling FIGURE 2. Relationship between survival and production during one year in 20 ponds at an Alabama shrimp farm. Modified from Chumnanka et al. 2015.
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