Fish in aquaponics
Water quality for fish
Chapter 2 discussed water quality for aquaponics. Here, the most important water quality parameters are listed again briefly and summarized in Table 7.1. Nitrogen Ammonia and nitrite are extremely toxic to fish, and sometimes referred to as “invisible assassins”. Ammonia and nitrite are both considered toxic above levels of 1 mg/litre, although any level of these compounds contributes to fish stress and adverse health effects. There should be close to zero detectable levels of both of these in a seasoned aquaponic system.
· Food and Agriculture Organization of the United NationsProduct quality
In cultured fish, particularly freshwater species, there is often the risk of off-flavour. In general, this reduction in flesh quality is due to the presence of specific compounds, the most common of which are geosmin and 2-methylisoborneol. These secondary metabolites, which accumulate in the lipid tissue of fish, are produced by the blue- green algae (cyanobacteria) or by the bacteria of the genus Streptomyces, actinomycetes and myxobacteria. Geosmin gives a clear muddy flavour, while 2-methylisoborneol gives a mildewed taste that can severely affect consumer acceptance and disrupt the marketability of the product.
· Food and Agriculture Organization of the United NationsFish selection
Several fish species have recorded excellent growth rates in aquaponic units. Fish species suitable for aquaponic farming include: tilapia, common carp, silver carp, grass carp, barramundi, jade perch, catfish, trout, salmon, Murray cod, and largemouth bass. Some of these species, which are available worldwide, grow particularly well in aquaponic units and are discussed in more detail in the following sections. In planning an aquaponic facility it is critical to appreciate the importance of the availability of healthy fish from reputable local suppliers.
· Food and Agriculture Organization of the United NationsFish health and disease
The most important way to maintain healthy fish in any aquaculture system is to monitor and observe them daily, noting their behaviour and physical appearance. Typically, this is done before, during and after feeding. Maintaining good water quality, including all of the parameters discussed above, makes the fish more resistant to parasites and disease by allowing the fishes’ natural immune system to fight off infections. This section discusses briefly key aspects of fish heath, including practical methods to identify unhealthy fish and prevent fish disease.
· Food and Agriculture Organization of the United NationsFish feed and nutrition
Components and nutrition of fish feed Fish require the correct balance of proteins, carbohydrates, fats, vitamins and minerals to grow and be healthy. This type of feed is considered a whole feed. Commercially available fish feed pellets are highly recommended for small-scale aquaponics, especially at the beginning. It is possible to create fish feed in locations that have limited access to manufactured feeds. However, these home-made feeds need special attention because they are often not whole feeds and may lack in essential nutritional components.
· Food and Agriculture Organization of the United NationsFish anatomy, physiology and reproduction
Fish anatomy Fish are a diverse group of vertebrate animals that have gills and live in water. A typical fish uses gills to obtain oxygen from the water, while at the same time releasing carbon dioxide and metabolic wastes (Figure 7.2). The typical fish is ectothermic, or cold-blooded, meaning that its body temperature fluctuates according to the water temperature. Fish have almost the same organs as terrestrial animals; however, they also possess a swim bladder.
· Food and Agriculture Organization of the United NationsAcclimatizing fish
Acclimatizing fish into new tanks can be a highly stressful process for fish, particularly the actual transport from one location to another in bags or small tanks (Figure 7.13). It is important to try to remove as many stressful factors as possible that can cause fatality in new fish. There are two main factors that cause stress when acclimatizing fish: changes in temperature and pH between the original water and new water; these must be kept to a minimum.
· Food and Agriculture Organization of the United Nations