The use of cleaner fish to control sea lice on farmed salmon has rocketed in a decade. In 2006 there were 700,000 in use by the Norwegian fish farming industry, and by 2015 that number stood at 26.5 million. This year 30 million lumpfish alone are expected to be produced.
But the use of the fish is not without problems.
“When you hold animals closely under conditions they are not accustomed to, you will always have a risk that they get sick. It is also not unproblematic that live fish are used as medicine and nursing assistants. The lives of cleaner fish in captivity are usually short, and farmers need to continually fill cages with new cleaner fish,” says Institute fish health officer Anne-Gerd Gjevre.
Both Gjevre and colleague Brit Tørud emphasise the importance of learning more about the species used as cleaner fish.
“We need more knowledge about cleaner fish biology, how they develop and their basic needs. To solve disease we first need to know what is normal for them”, says Tørud.
“In addition, we need to examine how they react to the environment in salmon cages and which bacteria, viruses or parasites can cause disease.”
Looking for microorganisms
According to fish health experts this is not an easy task, as it is not sufficient to determine what kind of bacteria, viruses or other cleaning fish die with, as they are not neccessarily those the fish die from.
“To look for unknown bacteria, viruses and parasites, we are dependent on the classical diagnostic methods of cultivation and and research on tissue samples,” says Tørud.
“We know for example that bacteria such as atypical Aeromonas and perhaps Pasteurella cause illness in lumpfish, but cleaner fish can presumably also be attacked by a number of other infectious agents that we cannot currently detect. So we must first determine which microorganisms cause cleaning fish deaths before we can create new methods that can detect these, and then develop vaccines.”
It is also pointed out that although the cleaner fish eat lice off salmon, they are exposed to their own louse parasite, Caligus elongatus.
“A study done back in 2007 by the National Veterinary Institute, Institute of Marine Research and the University of Oslo, showed that the lumpfish was one of the main hosts of this parasite. It was then found that wild roes had up to 700 lice.”