The pink salmon is often found in the cold waters of Canada and Alaska, where they are a staple part of the grizzly bear's diet. The translucent eggs of the fish are also known to make fine caviar.
Several of this species, however, were caught in UK waters about 10,000 miles away from their natural habitat and their presence has raised fears for Britain's native salmon.
The Environment Agency, which is conducting an investigation on how the fish arrived, said that the sightings were unusual albeit there had been earlier sightings of the species in previous years.
The agency said that the fish likely came from the Barents Sea near Norway and Russia, where there is a breeding program for the marine animal.
"We suspect these pink salmon may have come from populations which have established north of the Scandinavia and Russia area, rather than their original home of the north Pacific, but we can't be sure," a spokesperson for the agency said.
Although there is no evidence that the fish is breeding in UK waters, Paul Knight, from the Salmon and Trout Conservation Trust, said that if this alien species does breed here, it would cause pose a major problem to the endangered native salmon.
The pink salmon are an invasive fish and would compete for the same food as the native wild Atlantic salmon, which is not currently doing well in terms of population.
The British species is included in the International Union for the Conservation of Nature and Natural Resource's red list of threatened species.
Richard Jenkins, from the Environment Agency, said that they do not think that the pink salmon would likely cause a major effect on wild fish stocks at this stage.
The number of fishes that have been found would not likely cause any long-term problem and there were no recent reports of additional sightings so far. Nonetheless, he urged people to report sightings of the non-native fish.
"This is quite an unusual find in our waters. We are keen anglers know we are aware of the sightings and we are investigating," Jenkins said. "I would urge them to contact us if they see any non-native salmon in the waters, with a date, location and if possible a photograph, which would really help us identify them and build up a picture of where they are."
