This fish was seen by the website author in Osaka in July 2016, in the aquarium section of a pet shop in a large department store.
The basic fish is an oriental twintail: a fantail-shaped body with long finnage all round and a deeply forked tail; the colour is metallic orange. The opercula are curled forwards and much reduced, well balanced on both sides, clearly revealing all the gills and allowing them to protrude somewhat. The gills are a deep red colour (which has turned out rather purple in the photographs); they look delicate, yet the fish was swimming robustly and with no sign of affliction, despite its apparent vulnerability. The fish was in good condition, and was presenting itself well.
A few pictures have been seen over the years of goldfish with gills curled to mostly a minor degree, mainly in twintails, and looking like a fault; but nothing as dramatic as in this fish, which leads to the belief it was deliberate, i.e. the fish was bred to be a curled gill.
The aquarium staff were uncertain as to its identity, thinking it was a ryukin (but there is no dorsal hump). The fish must have found its way to the shop in error, for it was very cheaply priced.
Should you discover that a fish that you have bred or purchased has curled gills, then best advice is not to breed from it, and to leave the fish to live its life normally if it is not afflicted by the gill curvature and the exposure of the gills.
Curled gills are not curable, as they result from genetic mutation, so you should not expend effort in attempting to do so. As you can see from the above fish, they can, if housed with other goldfish, be left in peace.
© Bristol Aquarists' Society