Measuring growth weight is a better indicator of lumpfish health than commonly used indicators such as fin damage, according to researchers at the University of Stirling’s Institute of Aquaculture.
The researchers have developed a new tool to assess lumpfish welfare, which should help fish farmers to detect problems and take remedial action where required.
Lumpfish are increasingly being used in aquaculture to control sea lice numbers, but like other cleaner fish their own health can also be compromised.
Dr Sonia Rey Planellas at the Institute of Aquaculture has established a correlation between lumpfish growth weights and health outcomes.
She said: “At the moment, in the UK we use Operational Welfare Indicators (OWIs) for fish welfare, but lumpfish are a different shape to many other fish, so it’s about identifying the best indicators for each species.
“Fin damage is typically the indicator that is used, but in this study we found a more useful indicator was the correlation between growth weight relative to size and welfare.”
The researchers developed four indices based on weight and length comparisons, correlated with the OWIs for lumpfish, to develop a formula that calculates an overall score of above or below 2.8 (for other fish the figure is 3). Above 2.8 means the fish is fine, below means the condition is sub-optimal and farmers must take remedial action. Farmers input their measurements into a free online tool.
“It can help farmers calculate optimal times to introduce the lumpfish to the salmon, for example,” said Dr Rey Planellas. “Lumpfish can sometimes grow very fast, which leads farmers to introduce them too early, when the waters are still too cold. This is not good for welfare outcomes.”
Lumpfish are quite distinct from most farmed fish in terms of their body shape and behaviour, so the OWIs used to assess the health of salmon, for example, are not necessarily good indicators of cleaner fish health.
The researchers collected data from 456 fish from two different environments: a hatchery at Ardtoe in Scotland and in salmon sea cages in the Faroe Islands and Scotland, in conditions approved by the University of Stirling’s Animal Welfare and Ethical Review Body.
The paper, Using model selection to choose a size-based condition index that is consistent with operational welfare indicators, is published in the Journal of Fish Biology.
Dr Rey Planellas is also co-author on a new paper analysing the knowledge gaps in lumpfish farming. Addressing the welfare needs of farmed lumpfish: knowledge gaps, challenges and solutions is published in Aquaculture Journal.
The project was a collaboration between the University of Stirling, including modelling by lecturer Bruce McAdam; the Scottish Aquaculture Innovation Centre (SAIC); the Fisheries Society of the British Isles (FSBI) and several salmon companies. Its focus was to improve non-medicinal measures to manage sea lice.
Jim Treasurer, a scientist with Fai Farms near Fort William, worked on the study. He said: “This tool will help farmers identify fish that are below average condition for the population in the cage, and will indicate a need for prompt, remedial action, such as modifying feed.”
Ralph Bickerdike, Head of Fish Health and Welfare at Scottish Sea Farms, who participated in the study, said: “The welfare indicators identified from the project have since been adopted at those of our farms using lumpfish to help control sea lice levels and have proven hugely helpful in ensuring high welfare standards among our cleaner fish.”