also: うお
noun
General term for fish as an animal or food. The reading さかな is standard; うお appears mainly in compounds or literary contexts.
今夜の夕食は魚だ。
Tonight's dinner is fish.
川で大きな魚を釣った。
I caught a big fish in the river.
Standard kanji spelling; the most common reading is さかな.
Alternate reading うお is used in some compounds and older contexts, but さかな is far more common in everyday speech.
The kanji 魚 is a pictograph of a fish. The reading さかな is of native origin, while うお is also native and older, now largely replaced by さかな in modern usage.