Yes. Goldfish don’t have a stomach. They have a very long intestines where digestive process happens. So this fish has intestines which more than twice longer than their body length. and guess what ! Goldfish do have teeth too! How many of you did know that ? Here look at Goldfish teeth (Photo)
Ok so this is how the whole process happens. Their teeth located in back of the throat. Food gets crushed into smaller pieces once get there. Then food goes into a tube called the oesophagus which squeeze all water out of food. After that food goes through those long line of intestines. There are cells in digestive tract which create enzymes that act on carbohydrates, breaking them down into sugar.
The whole digestive process usually takes around 16 hours and slows down when weather gets colder. So this is an important piece of information. Feed less your pond goldfish in winter. They won’t stop eating so food would end up rotting inside their bodies.
Another problem is this whole thing happens nonestop so Goldfish are just keep eating and pooping. Since there is no stomach, food is not stored inside body. It’s just keep moving inside digestive tract. Because of this you should feed them several times a day in small amounts than one or two big meals.
Also it’s not bad to fast then twice a week or so. Just for let them to clean all leftover food inside their intestines. Their main food source is various plant matter even thought they don’t mind eating anything they can find. Problem is Goldfish digestive system made to digest carbohydrate than protein. So adult Goldfish should not be feed with high protein food too often.
Goldfish-specific food should have less protein and more carbohydrate than conventional fish food. Specially for fancy Goldfish types. If you are looking for types of Goldfish food to buy then check Hikari brand. They do have a wide range of food products specially made for various types of Goldfish.