My Full Red Ranchu for your scrutiny
 

Kindly make comments on this 15 month old (Approximately) ranchu that is 17.5 cm long. This is a female ranchu. Make a guess the Breeder and Country of Origin.

Very nice topview. The tail looks a little stiff. I would guess it's a Kashino bloodline, Thai fish, Aod Koban special perhaps? Just a wild guess. How about showing us a sideview? I only have one comment that the fish is very skinny. :)

What is the different between long body ranchu and skinny ranchu?

Your fish's stomach does not reach the tail. Look at one of the competition fish in the Nisai classes in the Kingyo Densho and you will see that the stomach need to be more complete. Then the tail of your fish will also improve. Currently the tail looks a bit too hard.

How to fatten it and also make the tail soft?

Try changing the water 100% at five days and increase one meal. Make sure you are not feeding more quantity. The tail will take care of itself, nothing you have to do. This is an adult fish and when it has gain a bit of size the tail will improve tremendously.

How does more regular water change helps. What are the chances of this ranchu becoming a champion?

Tail looks stiff, if i am not wrong when u see it swimming it looks more like the whole tail swaying left right like a cupboard. But i must say excellent colouration , smooth , even, and prominent. Beautiful piece. As for body size and structure well , looks good to me. Oh careful with the head growth...too pertruding also a problem in terms of overall balance of the Ranchu.