World Aquaculture December 2019

56 DECEMBER 2019 • WORLD AQUACULTURE • WWW.WA S.ORG to increase water extraction and to raise water use efficiency to minimize the dangers of water deficiency. The technological means to do this, such as wider use of efficient irrigation methods, wastewater recycling, collecting drainage and flash-flood water as well as improved low-cost desalinization technologies, are within our reach. Proper development of aquaculture is one of the important activities in this direction. Amajor protein source to populations living in dry areas are livestock, mostly cows and sheep, the existence of which depends on forage that grows yearly if rain is sufficient. However, in droughts, and even more during repeated droughts, rainfed pasture is not there to support the animals and there are not enough water impoundments to supply drinking water to the cattle. Such conditions lead to massive mortality of cattle (Fig. 2) and a severe lack of animal protein for subsistence farmers. Counterintuitively, aquaculture has the potential of providing animal protein in dry regions. Aquaculture of fish in ponds seems to require large volumes of water for production, mostly from losses by evaporation, infiltration or drainage. On average, evaporation and infiltration water losses from ponds are about 3.5 m/yr (Verdegem et al . 2006). In deserts, the yearly potential evaporation from ponds can reach 2-3 m/yr. For annual fish production of about 1 t/ha, as is common with many extensive ponds, water consumption is 35 m 3 /kg fish, a vast amount of water that cannot be obtained under arid conditions; however, with greater intensity, water consumption can be reduced tremendously (Table 1). A production level of about 1 t/ha-yr is quite common but a production level of 100-1000 t/ha-yr is achievable in biofloc ponds or in recirculating systems. Investing less than 100 L of possibly low-quality water to obtain 1 kg fish (0.1 m 3 /kg) is feasible, even under arid conditions. Intensified production leads to water saving when the production takes place in limited and possibly zero water exchange systems. Examples include biofloc technology (BFT; Avnimelech 2015) or recirculating aquaculture systems (RAS; Timmons and Ebeling 2007) or aquaponics (Rakocy et al . 2016, Kotzen et al. 2019). With aquaponics, nutrient-laden water from the fish tank is recycled through the root-zone of a hydroponics plant plot, where nutrients are taken up by the plant and filtered by the media. The purified water returns to the production tank. Each of these intensive systems has benefits and costs and can be adapted to conditions in different countries. Fresh water is needed to produce some of the plant ingredients of fish feed. The amount of water invested in feed ingredients depends on the type of animal produced (fish, shrimp) and the specific way plant crops are produced, but approximately 3 m 3 water is used to produce the feed ingredients needed to produce 1 kg fish (Verdegem et al. 2006). In addition to indirect water consumption, feed is a major part of the total expenses involved and, in most cases, this fraction of the expenses is the main factor that determines the feasibility of growing animals under variable sets of conditions. The cost of production is critical to aquaculture development, especially so in dry regions. The Feed Conversion Ratio (FCR) is the term defining the weight of feed in animal production (not considering the specific cost for different feeds). Animals that live in water float in the water rather than spending energy to withstand gravity, do not spend energy to control body temperature to be different than the environmental temperature, and therefore need less energy than terrestrial livestock that must expend energy to counter the forces of gravity and to maintain a constant body temperature. Thus, FCR in aquaculture is usually lower than that of terrestrial farm animals (Fry et al . 2017), being 6.0-10, 2.7-5 for cattle and pigs, respectively. Poultry grown for meat has an FCR of 1.7-2.0 because of effective genetic selection and holding of the animals in enclosed temperature-controlled cages. Additionally, the pond system can be used in some cases to produce natural feed fromwaste products, either waste materials produced in the pond itself or external waste materials such as home feed residues. Other organic materials can be metabolized by the pond biota to produce microbial biomass (biofloc) and zooplankton (copepods and others) that can provide a portion of the feed supplied to the fish and reduce the requirement for manufactured feed. Conclusions Production of fish as a basic source of protein to population of dry regions is a viable alternative, especially so as under series of droughts induced by climate change. With proper technology and selection of fish, it is possible to produce fish at a water efficiency of about 100 L/ kg or less as compared to much higher consumption with conventional aquaculture or conventional terrestrial livestock production. However, there is a need for further developments, adaptation, training and guidance. We need to adapt the presently known technologies to conditions suitable to the different regions where arid-land aquaculture TABLE 1. Estimated pond water losses (evaporation + infiltration) per kg fish produced as a function of production intensity. Production rate (t/ha*yr) 1 10 100 1000 Water losses (L/kg) 35,000 3,500 350 35 Counterintuitively, aquaculture has the potential of providing animal protein in dry regions. Production of fish as a basic source of protein to population of dry regions is a viable alternative, especially so as under series of droughts induced by climate change. With greater intensity, water consumption can be reduced tremendously. With proper technology and selection of fish, it is possible to produce fish at a water efficiency of about 100 L/kg or less as compared to much higher consumption with conventional aquaculture or conventional terrestrial livestock production.