Giving the wrong type of feed to young ballan wrasse could seriously impact their health, researchers at Nofima – the Norwegian Institute of Food, Fisheries and Aquaculture Research – have found.
A study of wrasse development found that young fish fed on extruded feeds – where the feed materials are processed at high temperatures – are far more likely to develop skeletal deformities than those given soft “agglomerated” feeds, which are processed at low temperatures.
In aquaculture, ballan wrasse are used as cleaner fish to help control sea lice numbers. Increasingly, because of concerns over the sustainability of using wild-caught wrasse, wrasse are being hatched and grown for commercial use. Cleaner fish health has become an important issue for the salmon farming industry.
The CleanFeed study at Nofima, which also involved collaboration with the Norwegian University of life Sciences, the Institute of Marine Research and leading fish farming group Mowi, looked at how juvenile wrasse fared when they were weaned from live food to dry feed.
Katerina Kousoulaki, feed scientist at Nofima, said: “In the first trial, ballan wrasse larvae that were weaned onto dry feeds had a good appetite for the hard, extruded feed, and we saw good survival rates. After a few weeks, however, the fish started to develop skeletal deformities. Fish that were fed a soft, agglomerated diet, a type of feed that is processed at low temperatures, appeared to have far lower deformity rates.”
As many as 41% of fish fed on extruded feed developed deformities, while only 2% of those on the agglomerated feed did so. The fish on the extruded feed regime also showed lower take-up of minerals from their feed.
The scientists at Nofima have developed a theory that high extrusion temperatures make feed minerals difficult to access for a fish species like ballan wrasse, which has no stomach or acid digestion.
The research also found that wrasse prefer shrimp or krill-based feed to conventional fishmeal, but will accept cod as an element in feed.
Senior scientist Ingrid Lein, project manager of CleanFeed project said that reducing the extent of deformities is essential for the welfare of the fish, and feed processing can play a role.
She added: “What is clear from the trials is that conventional high temperature extrusion, which is normal for salmon feed, does not work for this fish species. However, there continues to be a lot of deformities in ballan wrasse despite the fact that feed companies are taking action, so I think that the problem is more complex.”