In general most fish do quite well on one feeding per day. However, some owners prefer to feed their fish twice a day. Regardless of one or two feedings, the key is to keep the feedings very small. The timing is not critical, with the exception of nocturnal feeders, such as certain catfish. If you have nocturnal fish in your tank, be sure to feed them just before turning the lights out at night.
There are some exceptions to the once per day feeding rule. Herbivores (vegetarians) need to eat frequently because they do not have large stomachs to hold a lot of food. In nature they would graze all day long on plants. They should be given several small feedings a day, or provided with live plants they can nibble. Newly hatched fry and young fish not fully grown, require more frequent feedings of special foods designed for fry.
A good rule of thumb is to feed no more than the fish will consume completely in less than five minutes. When in doubt, underfeed! You can always give them another small feeding if necessary. However, if you overfeed the uneaten food will produce by-products which can be harmful to the fish. In the event you do overfeed, promptly remove the uneaten food using a siphon or net. keep in mind that not only the amount but the type of food is important.
