7.4.3 Catfish

Main commercial types:
Channel catfish (Ictalurus punctatus)
African catfish (Clarias gariepinus)

FIGURE 7.9
Line drawing and photograph of an African catfish (darias gariepinus)

Description

Catfish are an extremely hardy group of fish tolerating wide swings in DO, temperature and pH (Figure 7.9). They are also resistant to many diseases and parasites, making them ideal for aquaculture. Catfish can be easily stocked at very high densities, up to 150 kg/m3. These stocking densities require comprehensive mechanical filtration and solids removal beyond that discussed in this publication. The African catfish is one of many species in the Clariidae family. These species are air breathers, making them ideal for aquaculture and aquaponics as a sudden and dramatic drop in DO would not result any fish mortalities.

Catfish are the easiest species for beginners or for aquaponists who want to grow fish in areas where the supply of electricity is not reliable. Given the high tolerance to low DO levels and high ammonia levels, catfish can be stocked at higher densities, provided there is adequate mechanical filtration. Regarding waste management, it is worth noting that suspended solid waste produced by catfish is less voluminous and more dissolved than that of tilapia, a factor that facilitates greater mineralization. Like tilapia, catfish grow best in warm water and prefer a temperature of 26 °C; but in the case of African catfish growth stops below 20-22 °C. The physiology of catfish is different from other fish, as they can tolerate high levels of ammonia, but, according to recent literature, nitrate concentrations of more than 100 mg/litre may reduce their appetite due to an internal regulatory control trigged by high levels of nitrate in their blood.
Catfish are benthic fish, meaning they occupy only the bottom portion of the tank. This can cause difficulties in raising them at high densities because they do not spread out through the water column. In overcrowded tanks, catfish can hurt each other with their spines. When raising catfish, one option is to use a tank with greater horizontal space than vertical space, thereby allowing the fish to spread out along the bottom. Alternatively, many farmers raise catfish with another species of fish that utilize the upper portion of the tank, commonly bluegill sunfish, perch or tilapia. Catfish can be trained to eat floating pellets.