first let me say, thanks for sharing and i can see why you'd be proud of your artwork.
The "koi" is obviously a longfin ( in japan known as hirenaga) as opposed to nishikigoi, which is standard carp shape no elongated pectrorial and tail fins. In japan the red on the head is referred as tancho after their cranes. It is held in deep appreciation as it mimics their national flag. In koi shows it has a classification of it's own. very hard to get a good one that is naturally occuring. As one year olds these marks are often, surgerized to produce a perfect shape. If not done correctly as they grow you can see a yellow halo surounding the red.
Most koi spawns have 250 thousand babies to cull down to several hundreds. Tancho's occurr about 2 to 3 % of the total spawn, hence they can be very expensive,