Tokis-Phoenix
^_^
Its pretty much impossible to say what are "The most" rare or sought after fish in the uk, but for some pretty rare and sought after fish in general;
1. Blue eyed pleco/Panaque suttoni
2. Zebra pleco
3. Arowana's in general (particularly the platinum arowana's, often sell for thousands of dollars/pounds)
4. Rays in general
Koi can also be particularly sought after depending on the quality and size/age of the koi and its markings and colouring.
I've also heard albino betta's are quite rare, but as far as i'm aware they tend to have a lot of health issue's and often don't live very long so aren't that sought after despite their rarity. In fact a lot of rare albino varieties of various fish are very sought after.
1. Blue eyed pleco/Panaque suttoni
2. Zebra pleco
3. Arowana's in general (particularly the platinum arowana's, often sell for thousands of dollars/pounds)
4. Rays in general
Koi can also be particularly sought after depending on the quality and size/age of the koi and its markings and colouring.
I've also heard albino betta's are quite rare, but as far as i'm aware they tend to have a lot of health issue's and often don't live very long so aren't that sought after despite their rarity. In fact a lot of rare albino varieties of various fish are very sought after.