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Sick and injured farmed salmon are a problem, but researchers have recently developed an implant that uses sensors to gather information about the welfare of individual fish.

“Fish welfare must be improved. To achieve this, fish farms need information about the welfare of the salmon they are raising. Currently, however, we have very few methods for investigating the health of individual fish,” Eirik Svendsen says.

He is a research scientist at SINTEF Ocean. He and colleagues are now working to develop technologies that will provide us with new knowledge about the welfare of farmed fish.

Fish welfare is a relevant issue

There are already a lot of technological tools that can help us observe and gather data about fish behaviour in net pens. This is what researchers call behaviour at population and group level.

“We need a higher resolution on the welfare scale so that good welfare is not simply alive and bad welfare is dead,” Svendsen says.

There are many issues the industry needs to look into:

• How is the health, growth, and welfare of individual fish influenced by different factors in their immediate environment? 
• What is the influence of the design of a fish farm facility? 
• What about the placement of individual net pens within the overall facility design?

Provisional results from the research project RACE Welfare indicate that fish farm design does exert a major impact on fish behaviour. This is probably because it influences the level of exposure of the fish in individual net pens to prevailing waves and currents. 

“It will be interesting to monitor and compare several individual fish in net pens within a given facility under the highest and lowest levels of exposure, respectively,” Pascal Klebert says. He is a research scientist at SINTEF.

However, to be able to interpret observations from a given population, researchers must examine the behaviour of individual fish under many different conditions.

“In practice, we need to gather a forest of data on the various aspects of fish behaviour before we can identify the ‘trees’ – the things we really want to know,” Svendsen says.

Advanced implant offers new opportunities

The newly developed implant will be used to gather data. It is designed to acquire larger volumes of data than any other existing system – and all of it simultaneously. 

Moreover, the fish don’t have to carry several different sensors in their abdominal cavities. The implant is cylindrical – just 47 milimetres long with a diameter of 13 milimetres. It contains a battery, a memory card, and a microcontroller. It is fitted with measuring devices for gathering data on blood oxygen content, heart rate, levels of activity, directional orientation, and temperature.

“It hasn’t previously been possible to gather all these types of data simultaneously,” Svendsen says.

He envisages a future system whereby a selected group of so-called ‘sentinel’ fish, fitted with implants, will be introduced to each net pen in a given facility. The sensors in the implants will gather data that will be used to determine a ‘welfare score’.

“It will not necessarily always be appropriate simply to use a single, precise score. However, based on our existing knowledge, an acceptable score can be defined as a threshold value. When the microcontroller in the implant analyses the data, it will send a message if the score falls below the acceptable welfare threshold. This will give fish farm operators clear notification to start investigating for causes and implementing measures in the net pen where the poor score is recorded,” he says.

Are the fish inconvenienced by the implant?

According to Svendsen, so-called welfare-related indicators such as heart rate and swimming activity become normalised after a given period following insertion of the implant.

“On this basis we can assume that a fish has recovered and is not being inconvenienced to any great extent by the implant. However, complications such as infections may arise, so this is a complex issue,” he says.

Naturally, the fish need to be large enough to accommodate an implant, even though it is relatively small. 

“Fish should also be allowed time to recover after insertion. This is important because it will minimise any negative impacts that may bias the results,” he says.

Real world application

The first new task for the researchers is to improve the design of the implant. 

“We’ll be conducting thorough tests on fish in swim tunnels, combined with data acquisition in net pens,” Svendsen says.

It is important that the new measurement approaches are applicable at full-scale in fish farms under operational conditions. 

“We can do a lot of clever stuff in the lab but, in this project, we want to measure the links between physiology and behaviour in the real world where farmed fish actually live,” he says.