Never really looked at it that way before, but there is at least 1 fish I know of falling under that criteria. The emperor loach.To me a rare fish might be one that comes from a country where politics doesn't allow collection.
Loach enthusiasts often refer to the "Holy Grail". That highly desired species that is virtually unobtainable. For Botia lovers, this is definitely the species that fits that name. Despite having been known since 1993, very few fish have ever been exported and will always command a high price because of rarity and desirability.
Part of the problem that creates the high price is the pure logistics of obtaining the fish from the wild. The Tenasserim area is dominated by the Tenasserim Range, which reaches a height of 6,801 feet (2,074 m), and is bisected by the Tenasserim River, which flows south to the Andaman.
This whole area of old Burma (now Myanmar) is a hot-bed of ethnic insurgent groups fighting government forces. Up until 2003, one supplier was able to obtain these fish using an illegal logging and cigarette smuggling route, but the route has since been blocked by Myanmar's military as part of their war against the local Karen rebels. Large areas are land-mined unfortunately, and this means nobody dares to enter the area.
The Tenasserim River can alternatively be accessed via the border with Thailand, but permits and armed escorts are required adding to costs. To bring fish out requires the assistance of porters and the journey takes 3 days and requires traversing two mountains.
It is hardly suprising that any examples of this species that actually make it out of their native country will command very high prices indeed. Even if hostilities finish, the land-mine presence will create long-term safe access restrictions.
Emperor Botia (Botia udomritthiruji) — Loaches Online
www.loaches.com