The principle of using sonar for feeding can reduce the waste of feed in the breeding cages.Photographer: Erlend Astad Lorentzen / Institute of Marine

Echo sounder lets you know when the farmed fish is full

Then the feeding stops. The result is zero waste of feed and good growth for the fish, shows a new study.

"We have now verified that it is possible to achieve peak growth on the fish and avoid feed waste by using automatic feeding control. And that it works with both small and large salmon both in winter and summer".That's what ocean researcher Ole Folkedal says.

For several years, he and his colleagues have been researching how the use of echo sounders can reduce waste of feed in the farming industry . New results from the project have now been published in the scientific journal Aquaculture .

The idea behind the Echofeeding project is that an echo sounder more efficiently shows the amount of fish gathered at the food, and when the "meal" dissolves. Then the feeding stops automatically.Photographer: Erlend A. Lorentzen / Institute of Marine Research

Measures the biomass around the "food dish"

Briefly, the method is this:

Sonar measures the biomass, i.e. the amount of fish, in the feeding area in a cage. When it is feeding time, hungry fish will swim to the area and eat. When they are full, the fish move away. There are therefore fewer fish in the feeding area and the meal ends automatically at a predetermined minimum level of biomass. Put another way: The researchers have decided in advance that when the amount of fish at the meal drops to a certain level, the meal ends.

This means that there is no unnecessary feeding to fish that are already full, and no feed is wasted.

The color spectrum that the sonar creates

On the sonar you can see when the fish move higher up in the water, where the feeding takes place.

Principle from the 90s

The principle is not new. The method was developed at HI's capture section in the early 1990s.

"At the time, they roughly knew how such a system could be set up. Now we have brought the principle up from oblivion again and tested it with new software and hardware", says Folkedal.

"And then we have gone more into the biological and technical criteria to make it work. Our article is a kind of user guide for how salmon can be fed autonomously. The results are also relevant for feeding strategy and feeding control on a general basis", he adds.

Tested different meal rates

The experiments in the study took place at HI's research station in Austevoll. The new feeding method was tested on approximately 12,000 salmon in three cages. In summer, the experiments were carried out on salmon of around one kilogram and in winter on salmon of around 5.5 kilograms.

Among other things, the researchers have looked at the feeding intensity. That is, how quickly the meal should last. First, the fish got used to eating for eight hours every day. Then the researchers gradually halved the meal rate: four, two and finally one hour each day.

"What we see is that when we increase the pace of feeding, i.e. have a shorter meal, the salmon respond more strongly. You attract more fish if you shoot out many pellets than if you serve few pellets", says Folkedal.

Then the sonar also gets a stronger signal of appetite and it becomes easier to control feeding.

Author: Anders Jakobsen / Institute of Marine Research

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