6.4 Microbial Equilibrium and Enhancement in Aquaponics Units

Productivity in aquaponics system involves monitoring and managing environmental parameters in order to provide each component, whether microbial, animal or plant, with optimal growth conditions. Whilst this is not always possible given tradeoffs in requirements, one of the key goals of aquaponics revolves around the concept of homeostasis, wherein maintaining stability of the system involves adjusting operational parameters to minimize unnecessary perturbations that cause stress within a unit, or detrimental effects on other components. With ever-changing microbial assemblages, homeostasis never implies a permanent state of equilibrium, but rather a goal of achieving as much stability as possible, particularly within water quality parameters.

A RAS coupled to a hydroponics system will be ever-changing, but within this configuration, the RAS component remains relatively stable, particularly in decoupled systems (Goddek and Körner 2019). The hydroponics system, on the other hand, tends to be more erratic in water quality since the plant crops are often harvested in batch modes, and rarely in synchrony with fish production.

During the initial start-up phase of any aquaponics system, water quality — particularly with regard to microbial communities in biofilters — is a concern, and in order to minimize proliferation of opportunistic bacteria, a routine practice has been to allow microbial maturation of intake water before its introduction into the RAS, adding fish only after the capacity of the biofilters matches the carrying capacity of rearing tanks at a particular stocking density (Blancheton et al. 2013). A similar practice is observed in hydroponics where at least a portion of recycled water is used to inoculate a new crop, given that mature microbial communities take time to develop and introducing all new water results in long lag times. Such practices lead to greater stability in culture conditions and greater productivity. For instance, improved performance in RAS systems has been noted when the pre-intake filter is supplied with pulverized fish food to develop microbial communities more similar to those in the rearing tanks (Attramadal et al. 2014).