Unlike cats or dogs, fish don’t make sounds to tell you when they are hungry. It is hard to tell if your fish are truly hungry, so you want to be careful not to underfeed or overfeed your fish.
Most fish only eat once per day. You will know if you are feeding them too much when you see excess food floating to the top or bottom of the fish bowl/aquarium tank, depending on the type of food you use (flakes vs. pellets). It is important not to overfeed your fish as the excess food will lead to algae formation. If you have time to watch them eat, you will see how much food is being eaten, and any excess you should try to remove as soon as possible, to keep the bowl/aquarium clean.
Many fish owners use a “2 minute rule”- where they feed their fish and wait 2 minutes to see how much food is being consumed in order to determine the right amount of food required.