Ichthyomancy
It’s a divination form using fish as medium.

I Ching
Pronounced "Yee Jing", the Chinese Book of Change has been used in divination for millenia and is possibly the oldest book in the world. It has been amplified and refined over centuries, but the first legendary figure to be associated with its authorship was Fu Hsi, a ruler of China around 3000 BC to whom the discovery of eight trigrams was attributed.