From a fan composition by Katsushika Hokusai (1760 – 1849). See discussion.
Calligraphy
The kanji character below is the Japanese word for koi for those who want to practice their calligraphy.
This relatively simple koi sketch is for practice.
My koi is done entirely with sumi. Some parts of the body use dark sumi (nōboku), some use medium sumi (chūboku), and some I've left white. You can use gansai (colors) if you wish with some areas using stronger colors than others.