Automatic feeders
The automation of feeding requires knowledge about the feeding habits of the species in question. We also need to know technical details, such as the number of fish in each tank and their sizes. Manual feeding has advantages, as mentioned above, and is still used to ‘keep in touch’ with the fish. Nonetheless, technological developments can facilitate this labour. Nowadays there are many types of automatic feeders, especially for large-scale projects with a large biomass. Here we focus on the different types of automatic feeders used in RAS.
Normally the feed to be distributed is dry and pelleted, and placed directly into the tank where it may float for a time, but eventually it will tend to sink to the bottom. Most fish eat the feed on the surface or on its way down the water column, before it reaches the floor of the tank. Many species used in aquaponics are predators in the natural habitat and show aggressive behaviour when eating, which can lead to problems. Most modern automatic feeders take this fact into consideration, since poor feeding with inadequate feeders can lead to populations with dominant individuals who eat in excess, while the more submissive individuals go without. The immediate consequence is a higher variety of sizes in the tank (more intraspecific diversity in live weight), which makes it necessary to classify it more often, in order to break the social hierarchy and increase feed efficiency. Automatic feeders can be divided into two large groups, related to the biomass of fish and the quantity of feed to be distributed:
Feeders for juveniles: these distribute small rations at a high frequency (5-10 times a day). The pellet is very small and feed can be stored directly on the feeder and refilled by hand.
Feeders for on-growing: these distribute large quantities of feed at a relatively low frequency (1-3 times a day). Pellets are large and feeders are refilled by hand or automatically.
The cost of manually feeding fish is quite high in terms of time dedication needed to distribute it. The following company web sites provide details of feeder designs available for different species and aquaculture farms (www.acuitec.es; www.akvagroup.com; www.aquacultur.de). The basic parts of on-growing feeders are:
Storage or deposits for different types of pellets which originate from feed bags or silos delivered by truck.
Distribution of feed from the deposit onto the distribution site at the tank. Tubing runs from the storage site to the automatic feeder, which in turn has a small deposit. At this stage pellets are moved using mechanical systems or compressors and air injection. This equipment is quite specialized in order to ensure correct supply and adequate hygiene. Examples of the degree of sophistication of the feeding systems used in intensive aquaculture can be found at AKVA group. Some companies also use feeding robots for fingerlings in RAS, which is an automated way to fill up deposits near the tank. The robots move throughout the building using guides or rails that hang from the ceiling (see for example Crystalvision).
Distribution site
This is the final part of the automatic feeding system. Here the feed has to be spread out on the surface of the tank all at the same time, thereby allowing all the fish to feed simultaneously, which is better than placing the pellets in one small location. Thus, the distribution site is important for keeping the tank population more or less homogeneous.
Monitoring feed actually consumed
Recent technological developments allow one to detect when fish stop eating, which sends a signal to the automatic feeders to stop providing feed. These systems work with subaquatic cameras or acoustic and laser detectors, which let the feeder know when the appetite of the fish is waning.
Copyright © Partners of the Aqu@teach Project. Aqu@teach is an Erasmus+ Strategic Partnership in Higher Education (2017-2020) led by the University of Greenwich, in collaboration with the Zurich University of Applied Sciences (Switzerland), the Technical University of Madrid (Spain), the University of Ljubljana and the Biotechnical Centre Naklo (Slovenia).