Has UK aquarium bred the world's rarest fish?

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Tropiquarium has bred the Finescale splitfin, Allodontichthys polylepis — which it says is possibly the rarest fish in the world!

The fish is a livebearer belonging to a group of fish called Goodeids. There are about 40 species of Goodeids and their natural range is entirely within Mexico. Unfortunately, most of their habitats have high densities of human settlement and they are becoming increasingly altered and polluted. This has led to some species of Goodeid becoming extinct in the wild and others becoming critically endangered.

The story of what happened to this species in the wild is typical of other species. What happened to it in captivity, and how it came to be saved is not, as Tropiquaria explains:

"The story starts in 1987 when Dr. Alfred Radda, the Vice-President of the Haus des Meeres Aquarium in Vienna, found some of these fish when exploring in Western Mexico. He took a small number of them back to Vienna. Some of these were given to Stefan Herbert, who was able to breed them in small numbers. This group unfortunately died out in the late 1990s, but not before some had been passed to Michael KÅ‘ck, one of the aquarists at Haus des Meeres. He had, in turn passed small numbers on to other people.

"During this period, Professor Omar Dominguez, a field researcher in Mexico, examined the stream in which this species was originally found and could not find any trace of the species. Although the stream was unpolluted and biologically sound, there had been a long, recent dry spell in the area during which the stream had dried up. Professor Dominguez concluded that the species was extinct in the wild. This has since been confirmed.

"In 2008 Michael Kock (Vienna) gave his surviving fish to an expert fish breeder in Hungary. Sadly there was a car crash on the return to Hungary and all these fish were lost. Although then thought to be extinct there was a surprise, some fish had been given to Kees de Jong in the Netherlands in 2006. It was arranged that these fish, just eight in total, would be returned to Haus des Meeres in Vienna. Michael Kock, now curator in Vienna, collected them. He travelled by train, but even then the fish were nearly lost! On the trip to Vienna the train made an emergency stop and the case containing the fish slid a considerable length down the train. They survived though and subsequently bred.

"In 2013, Tropiquaria’s aquarist Shaun Stevens travelled to Vienna and accepted eight of the babies born there. These have recently bred and Tropiquaria now has 25 fish, out of only about 100 worldwide. Tropiquaria is now one of only two aquaria to exhibit this species (the other being Haus des Meeres in Vienna). It is hoped to return some to the wild in the future."