Developing a zooplankton challenge model for Atlantic salmon (FS141)

Project Outcome:

This project has provided a proof-of-concept that a challenge study with lab-reared jellyfish for salmon is feasible.

Gill disease is one of the most significant health challenges to salmonid culture in the marine environment. Harmful zooplankton, such as jellyfish or cnidarians, are thought to play an important role in disease development, but there is a lack of scientific and technical understanding of the interactions between jellyfish or cnidarians and fish gills that can only be obtained through a lab-based challenge model using lab-reared organisms. This project demonstrated that it is feasible to develop such a challenge model. Specifically, we were able to produce a pre-determined quantity of jellyfish at a pre-determined point in time, transport them, and challenge salmon with these live jellyfish. The aim was to develop gill disease in fish. However, we observed minimal gross gill disease in challenged fish, no histopathological differences between gills of challenged and non-challenged fish and no immune response, implying that the challenge model needs further optimisation. Therefore, the challenge model developed in this project will be a starting point for further optimisation of this model.

The demonstration of the feasibility of a jellyfish challenge to salmon is a major step forward in developing a standardised zooplankton challenge that may eventually help improve our understanding of the interactions between jellyfish and the salmon gill and allow us to investigate multifactorial gill diseases under controlled conditions, develop improved functional feeds for gill disease and evaluate existing and new mitigation methods.