The short answer
Your fish follow you because they’ve learned that you bring food. Over many feedings they’ve associated your appearance and movements with a meal, so they gather at the front of the tank and track you around the room hoping to be fed. It’s a sign of a healthy, relaxed fish that trusts its keeper — not a problem to worry about.
It’s learned behaviour
Fish are better learners than most people expect. Every time you walk up and food follows, the fish links you with the reward, and before long just seeing you triggers the response. This is the same recognition that lets fish tell their owner from a stranger — many will swim to the glass for the person who feeds them and stay shy around unfamiliar faces. For the science behind it, see do fish recognise their owner.
Following vs begging
There’s a fine line between a fish that greets you and one that begs constantly. Many fish will act “starving” at every approach, dancing at the glass whenever anyone walks past. Don’t be fooled into feeding every time — most fish are opportunists and will happily overeat, which fouls the water and causes health problems. Stick to a set feeding routine rather than responding to the performance. See how to tell if your fish is hungry and how often to feed your fish.
Make the most of it
You can encourage this friendly behaviour by keeping a calm, consistent routine — approaching gently, feeding at similar times, and avoiding sudden movements. A varied, quality diet keeps fish healthy and eager without needing large amounts; browse our fish food guides. If a normally-attentive fish suddenly stops following or eating, treat it as an early warning and check water quality with a test kit.