Koi

This fish is formed from the classic Fish Base, however the way the flaps are used is nontraditional. There are some outside reverse folds, squash folds and unusual reference points giving this model an " intermediate" level designation. Diagrams for this can be found in the book Origami by the Sea:

https://origamiusa.org/catalog/products/origami-sea

A single square of larger kami is recommended (10"/25cm). With more practice you can use smaller sheets. Of course, be sure to have red/white paper on hand for the classic color scheme.