After many decades of salmon farming, recent years have seen an increasing interest in studies into fish welfare. In particular, the fish farming sector is looking for better approaches to delousing. Researchers have now developed an electronic “sensor” fish that can be used to measure the external factors that affect fish during processes such as delousing.
Trondheim/Norway — The project Hydrolicer has been carried out by researchers to study a mechanical approach to the delousing of farmed fish. The method involves subjecting the fish to turbulence in a water chamber. Currents generated in the water mass effectively remove the lice from the fish with no need for chemicals. Now, researchers discovered that the physical trauma incurred prior to delousing was probably more stressful than the process itself.
The fish have to be moved from their cages into the delousing chamber using a pump system. In order to feed the salmon into the pump, they first have to be crowded together so that the system can move fish and not just water. This process can take an hour or more, while the actual delousing is completed in less than thirty seconds. The researchers also identified differences between pump systems. So-called ejector pumping, that works using high water pressures, exposed the fish to less physical stress (measured in terms of acceleration) than so-called impeller pumping, which moves the fish using a mechanical paddle installed in the water stream.
Facts about Hydrolicer
Hydrolicer is the name given to both a salmon delousing method and a delousing project funded by the Norwegian Fisheries and Aquaculture Industry Research Fund (FHF). Since the project launch in 2016, a cross-disciplinary team of researchers has been studying the effects of the pre-delousing corralling of salmon in their cages as part of the Hydrolicer method. One of the main findings of the Hydrolicer project is that pre-delousing corralling using Hydrolicer seems to stress the fish more than the delousing process itself. The results have encouraged the researchers to start looking for even more data on the stresses that caged fish are exposed to during a variety of operations, not least delousing.
Do Fish Feel Pain?
Researcher Ulf Gøran Erikson, originally trained as a chemist, also works with farmed fish. He has been a close observer of developments in the industry for many years, and has worked a great deal with veterinarians on many of his research projects. He says that there is an increasing volume of research suggesting that fish can feel pain, although to date this has proved difficult to measure.
Cyberneticist and researcher Walter Caharija has been looking more closely into what happens to the fish during the delousing process. Some of his results are now available as part of the Kvalisys project. This project aims to advance development of the sensor fish in order to obtain even more data linked to fish welfare.
The “sensor” fish is a cartridge-shaped object, about 50 cm long, containing electronic instruments and a small computer, designed to measure the responses of the fish around it. This is a big tube through which the fish are pumped from the inlet of one cage to the outlet of another. The instruments in the “sensor” fish instruments record temperature, pressure and acceleration and, not least, how the sensor responds to the time it spends in the pump system. Caharija, working together with the researchers from the Hydrolicer project, has developed an approach designed to reveal even more about fish welfare, and not least the links between how technology, mechanical stress and biological factors affect the fish. For this reason, the “sensor” fish is equipped with a series of instruments to measure acceleration, water pressure, light conditions and temperature. It has a pressure-sensitive surface and is fitted with a GPS tracker.
Measurements made during the “sensor” fish experiments are providing researchers with opportunities to further develop more sensitive delousing methods, which are highly sought after within the aquaculture sector, not least because fish welfare is now becoming increasingly more important at all stages of the value chain. This hasn’t always been the case. Researcher Ulf Gøran Erikson says that ten years ago, and before that, there weren’t as many inspections. Today, however, fish welfare was one of the most important priorities in the fish farming sector.
Next Step — Measuring Stress
Erikson emphasizes that they have not assessed all delousing methods currently in use, and that the “sensor” fish cannot help to meet all the challenges linked to fish welfare. “We’re talking about mechanical stress”, says Solvang. The “sensor” fish can’t tell anything about stress levels in fish — its electronics simply cannot measure this. At least not yet. Erikson and Solvang stated that new projects are being launched in order to investigate a number of aspects of fish physiology. The next step was to measure fish heart rhythms. Only then could the researchers arrive at some conclusions about how fish really respond to the various delousing methods.