Marine biologists want to take DNA samples from 120 rays in European aquariums to find out how diverse DNA is within the species, which will give clues as to how inbred individuals are.

This information will allow aquariums to pair up breeding adults that are more genetically diverse in the hope they produce healthier offspring. Inbreeding within a small breeding group can cause stillbirths and shorten individuals’ lifespans.

Undulate rays – which are found in the Atlantic including around the UK, and the Mediterranean Sea – are listed as endangered on the IUCN (International Union for the Conservation of Nature) Red List of Threatened Species.

Their dramatic decline has been linked to commercial fishing of the species, which was banned in 2009, and the fish is now a protected species in UK waters.

The gene mapping project is part of a captive breeding programme which began in 2010. Since its inception there have been 29 successful births of undulate rays at 10 aquariums in the UK.

The research team, from the University of Manchester and Weymouth Sea Life Centre, claims increasing the number of captive rays in aquariums will improve the public’s appreciation of the threatened fish.

“If numbers in the wild fall to a critical level it is feasible we could help with a reintroduction programme,” said marine biologist Jean-Denis Hibbitt, a marine biologist at Weymouth Sea Life Centre.

Undulate rays are named after the wavy pattern on their upper bodies. They grow to over 85cm in length and lay leathery eggs or “mermaids’ purses” which can often be found washed up on beaches. The fish can live for up to 20 years.

The team is screening DNA from the captive rays, and two from the wild, in a laboratory to build a unique genetic signature for each ray. “This will enable us to determine whether they are brothers, sisters, parents or distantly related to one another,” said researcher Graeme Fox, a PhD student at the University of Manchester.

Researchers also compiled a "stud book" and microchipped rays in aquariums in Europe to make their genetic information easier to track in the future.

Their work will allow aquariums to plan an “optimum management strategy” to secure the genetic health of the species. And the DNA testing could also be extended to wild populations of undulate rays to build an idea of their genetic health.

Mr Hibbitt said: “If it is found that the shrinking population has led to localised inbreeding it would sound alarm bells for the future survival of an iconic species in our waters.”