Further developing a zooplankton challenge model for Atlantic salmon

This is a full R&D project funded by the Seafood Innovation Fund (RD149).

This project successfully optimised an experimental model of gill disease caused by juvenile Aurelia aurita reared in the laboratory. Atlantic salmon post-smolts were exposed to A. aurita by: 1) the addition of A. aurita 1 cm medusae to tank water at concentrations from 150 to 1200 individuals per m3, for periods of 3 h to 72 h, and 2) direct inoculation of jellyfish onto a single gill arch of fish (under anaesthetic). Exposure effects were assessed using gross and histological gill scores. 

The most effective, reliable and efficient technique for jellyfish exposure was by direct inoculation. 

Histology scores were more specific and sensitive than gross gill scores. The reproducibility of the model was improved by ensuring fish had low background gill scores and by inoculating with three jellyfish per gill arch.  

Samples collected at 24h, 72h and three weeks post-challenge showed that pathology developed within 24h and persisted at 72 h, with some recovery by three weeks post challenge. Samples were collected at 48h post challenge in subsequent studies. 

Direct inoculation was used to test different life stages of A. aurita using 1 cm diameter juveniles and one centimetre pieces of larger medusae, both of which caused consistent histopathology, unlike the younger ephyra stage used in the feasibility study.

Other species used included: Clytia hemisphaerica (1 mm medusa, 10 per gill arch) which had no significant effect, although mild cnidarian-like associated histopathology was detected; Chrysaora sp. diced into 1 cm2 sections, which had a marked effect, while we were unable to demonstrate any effect with Muggiaea atlantica using this technique.

This is a follow-on project from an earlier feasibility study that was also funded by the Seafood Innovation Fund.   

The UK Seafood Innovation Fund supports new ideas to deliver cutting-edge technology and innovation to the UK’s fishing, aquaculture and seafood industries. Administered by the Centre for Environment, Fisheries and Aquaculture Science (Cefas) on behalf of the Department for Environment, Food and Rural Affairs (Defra), the programme encourages sustainable and innovative ideas to bring about seafood security, new partnerships across seafood and technology sectors, and to contribute to strong evidence-based management. Find out more about the UK Seafood Innovation Fund on its website.