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The first section in this chapter includes select information on fish anatomy and physiology, including how they breathe, digest food and excrete wastes. The feed conversion ratio (FCR) is introduced, important for all aquaculture, which refers to how efficiently the fish convert feed into body mass. Special attention is then devoted to the fish life cycle and reproduction as it relates to breeding and maintaining stocks. The care and health of fish in aquaponic units are then discussed, covering water quality, oxygen, temperature, light and nutrition. The third section identifies a number of suitable commercial aquatic species for aquaponics, focusing on tilapia, carp, catfish, trout, bass and prawns (Figure 7.1). The chapter closes with a final section on individual fish heath, diseases and disease prevention methods.
Standard manufactured fish feed pellets are recommended for use in aquaponics because they are a whole feed containing the correct balance of proteins, carbohydrates, fats, vitamins and minerals needed for fish.
Protein is the most important component for building fish body mass. Omnivorous fish such as tilapia and common carp need about 32 percent protein in their diet, carnivorous fish need more.
Never overfeed the fish, and remove uneaten food after 30 minutes to reduce risks of ammonia or hydrogen sulphide toxicity.
Water quality needs to be maintained for fish. Ammonia and nitrite must be close to 0 mg/litre as they are toxic at any detectable levels. Nitrate should be less than 400 mg/litre. DO should be 4-8 mg/litre.
Tilapia, carp, and catfish are highly suitable for aquaponics in tropical or arid conditions as they grow quickly and can survive in poor quality water and at lower DO levels. Trout grow well in cold water, but require better water quality.
Fish health should be monitored daily, and stress should be minimized. Poor and/or changing water quality, overcrowding, and physical disturbance can cause stress, which may lead to disease outbreaks.
Abnormalities or changes in physical behaviour can indicate stress, bad water quality, parasites or disease. Take the time to observe and monitor the fish in order to recognize symptoms early and provide treatment.
Source: Food and Agriculture Organization of the United Nations, 2014, Christopher Somerville, Moti Cohen, Edoardo Pantanella, Austin Stankus and Alessandro Lovatelli, Small-scale aquaponic food production, http://www.fao.org/3/a-i4021e.pdf. Reproduced with permission.