Researchers surprised by the reactions of penned fish to robots

After robotics made its entry into the aquaculture industry, aquaculture has mostly used equipment that is orginally developed for the oil and gas industry. 

“I thought that it would be quite straightforward to apply the same technology as we use in the oil and gas industry to the aquaculture sector. So, my first visit to a fish farm turned out to be a real wake-up call,” says Eleni Kelasidi. 

Kelasidi had a PhD in snake robotic technologies developed for use in the oil and gas sector before becoming a researcher at SINTEF Ocean.

“I never really fully understood that a net pen full of living, moving animals would change the conditions for robot operation so drastically. It’s very different from operating a robot in the open ocean where we investigate stationary, dead metal objects such as pipelines and turbines,” she says.

Kelasidi believes that more sector-specific robots are required. Her work has involved investigating technologies that cause the least possible disturbance for fish.

Safety margins – according to the fish

“When we talk about interactions between humans and robots, we take it for granted that we assign highest priority to the needs and safety of the humans,” says Kelasidi. 

She further adds that this same principle lies at the heart of their Fish-Machine Interaction project. 

"We want to contribute towards the development of better robots that can operate fast and efficiently. But they must of course take the needs and safety of the fish into account,” she says.

Eleni Kelasidi, post-doc Qin Zhang from NTNU, and the rest of the team have been gathering and analysing data for three years in various net pens installed at SINTEF Ocean’s full-scale fish farm laboratory, SINTEF ACE. The data collection has taken place at different locations, at different times of the year, and in different stages of the fish's life cycles. 

“We’ve carried out several different measurements for each situation, so our data gathering has been nothing less than comprehensive,” says Kelasidi. 

The study provides some very clear answers, not least on issues such as what a fish considers to be a safe distance from a given object.

“One thing that surprised us all is that the relationship between the size of a fish and the distance it keeps from an alien object is in fact linear: The smaller the fish, the narrower the safety margin,” the researcher says. 

A robot that is lowered into a net pen in reality blocks a greater volume of water than the equipment itself, and the safety margin that the fish maintain has an impact on how confined it becomes in the pen under different robotic operations. 

The results of this study will enable fish farm operators to be aware of the distances that the fish keep from the equipment they lower into their pens. 

For example, fish weighing five kilos keep a distance of three metres. In practice, the fact that younger, smaller fish maintain a narrower safety margin means that more equipment can be lowered into a pen containing young fish without impacting their swimming patterns and behaviour.

Colour, size, speed, and sound

“If we know what disturbs or impacts negatively on penned fish, we can say something about the technical adaptations that equipment manufacturers should be making,” says Kelasidi, who has since discovered more about how the fish respond – and what they overlook.

The research team built a number of objects in a variety of shapes, colours, and sizes, with the aim observing and quantifying any variations in the responses of the fish. 

It turns out that shape makes little difference. The fish respond identically in the presence of both cylinders and cubes. 

However, they maintain a greater safety margin in the presence of large objects compared to smaller ones, and they keep a greater distance from yellow objects than from white ones.

In other words, colour and size both have an impact. The same is true for sound and speed of alien objects, as demonstrated by previous studies.

The researchers hope that technology suppliers will use this information as they continue to develop new equipment.

“For us researchers, our goal is to continue to develop technologies that will enable autonomous robots to adapt their behaviour to the responses of penned fish with the aim of disturbing them as little as possible," Kelasidi says.

She offers an example: If a robot’s sensors detect that fish are keeping their distance, or if they recognise a change in behaviour in response to a potential stress stimulus, the robot may be able to reduce its speed and operate in a manner that causes less disturbance.

The goal is to enable robots to adapt

It remains unclear whether fish swimming away from equipment indicates a stress response or resembles children running away from someone chasing them in a game.

This area requires further investigation, the SINTEF researcher notes, highlighting that it is useful to know what behaviours fish exhibit in response to different stimuli.

According to Kelasidi, there are many factors that may play a role: If you intend to perform work in a net pen and at the same time keep the fish at a distance, it will be useful to know what colours the fish tend to avoid. If you want to get close to the fish in order to take pictures of them, it is a good idea to use a robot in a colour that causes the least disturbance.

At present, the research team has only tested yellow and white because these are the colours most commonly used by equipment suppliers. In the future, the team aims to investigate how fish respond when a robot rotates or moves, to what extent speed is a factor, and whether or not it matters if movement is horizontal or vertical, or with or without lights.

Kelasidi emphasises that the primary aim is to perform autonomous robotic operations with the least possible disturbance.

"Robotic technologies that take fish welfare into account will have no impact on the most pressing problems facing the sector today, but they will lay the foundation for improved welfare in the future,” she says. 

Reference:

Zhang et al. Farmed Atlantic salmon (Salmo salar L.) avoid intrusive objects in cages: The influence of object shape, size and colour, and fish length, Aquaculture, vol. 581, 2024. DOI: 10.1016/j.aquaculture.2023.740429

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