The oracle-bone scribes drew a fish exactly as you would spot one in a stream: a rounded head at the top, a spine running down the middle, a pair of scale-marks along its sides, and a tail flicking open at the bottom. Turn the picture on its side and you can still see the whole animal, nose to fin, in one continuous shape.
A piece of culture
A fish for every new year 鱼 (yú) sounds exactly like 余, "surplus" — so a whole fish, cooked whole and deliberately left half-eaten on the table, is the centerpiece of the Chinese New Year meal. Families wish each other 年年有余 — "may there be surplus every year" — and because it is a pun on 鱼, paintings, papercuts, and porcelain fill up with fish at New Year too. The character keeps swimming through the rest of the language: pair it with 羊 (sheep) and you get 鲜, "fresh" — a sheep and a fish were once the tastiest things a Bronze Age cook could serve.
Use it in a real word
木鱼
mùyú · muk6 jyu4
wooden fish — a hollow carved block Buddhist monks tap while chanting; you already know 木