Have analysed contaminants in "new" fish

Earlier this year, chefs at the Bergen gourmet restaurant Lysverket had the opportunity to prepare a restaurant dish using fish caught during one of the Institute of Marine Research’s deep-water surveys. The unusual item on the menu was the Mueller’s pearlside, a small fish the size of an anchovy. It’s rare to see the Mueller’s pearlside on a dinner plate, as these tasty creatures live 200 to 1,000 metres below sea level. The chefs’ conclusion was that this so-called mesopelagic fish tastes good and that they would be happy to serve it if they could get hold of it in larger quantities. But was it safe to eat?

“The deep oceans contain large quantities of fish, octopus, jellyfish and crustaceans that we don’t generally harvest. It is estimated that the world’s oceans are home to more than ten billion tonnes of these species, many of which could be used for human consumption or as food for animals and farmed fish. But before we start using these resources, we need to know what contaminants they contain”, explains Martin Wiech, a researcher at the IMR.

Found few toxics

Now scientists at the IMR have studied the levels of heavy metals and organic toxics in three potentially interesting mesopelagic species, at the request of the Norwegian Food Safety Authority. Those three are the Mueller’s pearlside, the glacier lantern fish and the spotted barracudina. The scientists found that most toxics were only present in low concentrations. The exceptions were the cadmium content in glacier lantern fish from the Norwegian Sea and the lead content in a pooled sample of spotted barracudina from the Norwegian Sea. This latter finding must be investigated further, since it was based on just one result.
 
The scientists also calculated what the toxic levels would be if you made fish meal and oil out of these fish. As most of the organic pollutants will follow the oil fraction, the contaminant levels in the oil and meal are different from those in a whole fish. Organic pollutant levels were generally found to be low, and well below the maximum limit in the oil, with the exception of the dioxin content in the glacier lantern fish, which was close to the limit. In fish meal they also found only small quantities of heavy metals.

Risk of diarrhoea

As well as studying common toxics like lead, dioxins and cadmium, the researchers also studied the wax ester content. This is an indigestible oil that can cause a kind of diarrhoea, called oily leakage. Wax esters are not found in most of the other Norwegian commercially caught fish. No scientific studies have been done on how much people can take of this oil, except scientists testing it on themselves. Using those tests as a reference, the wax ester content of the glacier lantern fish and spotted barracudina implies that you would need to eat a large portion before experiencing any stomach problems.

“Our findings show that these species can be used for human consumption, but preferably not in very large quantities at a time, mainly because the oil they contain may cause diarrhoea. There’s no problem having them as a starter, for example. You could compare it to sardines, which people don’t eat lots of at a time either. We also consider that there is great potential for using these species in fish feed”, says Wiech.

The scientists at the IMR have analysed the contaminants in three of the most promising mesopelagic fish species, but many other species and regions remain to be studied.

“This is just the start. There’s lots more work to be done”, says Wiech.