The Bubble

The process of collaboration

Two groups of fish were monitored closely – one which was PRV-1 positive, and the other which was PRV-1 negative. PRV is the virus which causes HSMI. Samples were taken from the fish and tests were conducted on a monthly basis, from the time they were put in the pen to the time of harvest.

‘Together with Ellingsen and the Faculty of Veterinary Medicine at the Norwegian University of Life Sciences, we did several types of analysis for several months – blood chemistry, gene expression, pathogen detection, and histology. We looked at all the data combined to get an overview and understanding of what was going on with the fish,’ says Delphine Crappe, Team Lead Biotechnology and Manager at The Bubble. Production data was compared and evaluated as well.

The PRV-negative fish tested positive in August 2020, three months after the project kicked off. One month later, in September, results showed a further decline. However, there were no indications from the production data, nor from appetite and mortality, which would indicate that an HSMI outbreak was imminent. In such a scenario, production would normally have proceeded as usual, without any action taken.

‘Thanks to close collaboration with NMBU and Ellingsen Seafood and the fact that we acted quickly, we were able to take the appropriate measures and initiate a feeding program to support the fish during the HSMI outbreak,’ says Johan Rennemo, veterinarian in Skretting Norway. According to Myrvold, the result of this well-timed intervention was a milder outbreak of disease in the group that was PRV-1 positive.

Targeted nutrition is beneficial to support sick fish

Health monitoring projects like this are intended to complement, not replace existing conventional approaches to fish health. Their power lies in the fact that they can equip fish farmers with knowledge on how to prevent an outbreak of disease – specifically which feed to use, when to use it, and on which group of fish.

‘We now possess a better understanding of how to be more precise in utilising functional feed in relation to a HSMI outbreak. Given that the diet includes a high level of marine oils, which are scarce and increases costs, it should only be used when necessary,’ says Mads Martinsen, Director of Product Development and Sustainability in Skretting Norway. Both companies have continued to collaborate on other projects since.

‘We’ve demonstrated that it’s possible to be one step ahead of HSMI, and we will continue working on targeted nutritional solutions that can help support fish with other diseases. In times of sickness these could have a major positive impact on animal welfare. The potential here is still untapped,’ says Rennemo.

A paper on this health monitoring project has been published in Veterinary Research. To read the full paper, click here

Five facts about histology at Skretting

1. We have been using quantitative histology, or the study of tissue, for more than 15 years. With this, microscopic slides are first scanned to produce digital images, before they are automatically analysed using software.
2. Histology is used to measure parameters of fish health. These can be used to quantify the level of inflammation in fish, when there is a change in the environment, or a change in diet. For instance, in the search for more sustainable alternatives to fish meal and fish oil, Skretting needs to test how fish react to new ingredients in feed.
3. When it comes to tissue examination, histology is the gold standard. Newer methods like microarray are complementary, and can in fact give a first response overview of what is happening inside the fish, since changes in gene expressions would manifest faster than in the tissues.
4. We have been using artificial intelligence since 2021 to 'turbo charge' the process of annotating and classifying tissues. Manually isolating a tissue of interest from 400 skin samples would previously take a pathologist 40 hours. On the other hand, after training AI to recognise the correct parameters, the AI can complete the task with greater precision in under an hour, while also extracting much more information such as colour, structure, and context.
5. Up close, the image on the right reveals a great deal of information. Green shows us general tissue, red represents inflammatory cells, blue is for goblet cells which produce mucous, and yellow is for vacuoles which are involved in nutrient absorption. By quantifying these – among other parameters – we can measure the level of inflammation in a fish.

Our biotechnology specialists have been working with cell culture at The Bubble since February 2022, and are motivated by the principle of the 3Rs: Replace, Reduce, and Refine. By using cells, we are able to replace and reduce the use of live animals in the lab.

The team works with immortalised cells from fish to help develop anti-inflammatory products, amongst others. The cells are maintained in a growing medium at a constant temperature, on average doubling their numbers every week, making this an efficient and cost-effective method for research. Primary cells are also extracted from various fish organs in order to cultivate them. Within a few hours we are able to obtain millions of cells from each tissue, providing excellent models for health or growth studies within aquaculture.

Cell culture will play an increasingly important role in the early stages of product development. In a recent experiment, muscle cells were isolated, and their growth rate measured. In the future, this could be applied to the study of new grower products for aquaculture species.