How do you know if farmed salmon have had enough to eat?

Well, according to Lingalaks fish farms in Norway, which produce nearly three million salmon each year, the fish make less noise once the feeding frenzy is over.

The firm knows this thanks to a new hydro-acoustic system it has installed at one of its farms. The system listens to the salmon sloshing loudly about as they feed in a cluster. When the fish have had enough, they swim off and the noise lessens.

Lingalaks chief executive Erlend Haugarvoll hopes this knowledge will save his firm lots of money in reduced feed, as much of it currently gets wasted.

\"I think it could improve [expenditure] by about 5%,\" he says. \"That could be between 7m-10m krone (£630,000-£900,000; $900,000-$1.3m) for our firm.\"

The system, developed by tech firm CageEye, has taken years to develop, says chief executive Bendik Sovegjarto.

\"It\'s not like a pellet detector,\" Mr Sovegjarto says, which observes the number of fish food pellets left in the water.

\"When you don\'t see any pellets, you can\'t be certain if it\'s because the fish are full or that you\'re looking in the wrong place because of the water currents.\"

Using audio data from the caged salmon is more accurate and could save Norwegian fish farms 1bn krone a year in un-gobbled feed, believes Mr Sovegjarto.

The technology has been developed with the help of Ole Folkedal, at the Institute of Marine Research, in Bergen. He has monitored salmon feeding patterns and other data, such as water temperature and oxygen levels, and this is giving scientists and farmers new insights into the factors influencing how much the fish want to eat.

\"You have huge variations in how much to feed every day,\" says Mr Folkedal.

Source: BBC // Original Article