鱼 (traditional 魚) is a clear picture of a fish — head on top, body with scales in the middle, tail at the bottom (now four dots, originally a fishtail/fin). One of the most recognizable pictographs once you know to look.
鱼 is fish — and a powerful symbol of abundance, because 鱼 (yú) sounds exactly like 余 (yú, 'surplus'). At New Year, families eat a whole fish for 年年有余 ('may you have surplus year after year') — and traditionally leave some uneaten, so the surplus 'carries over'. So serving 鱼 is serving a wish for prosperity. 钓鱼 = to fish; 金鱼 = goldfish.
Head, scaly body, tail — a FISH.
鱼 (fish) sounds like 余 (surplus), so a whole fish at New Year means 年年有余 — 'abundance every year'. Leave some uneaten and the surplus 'carries over'.