Yes! they will eat a lot just like most fish, they are all piggies
BUT it isn't a good idea to let them eat as much as they like - it can be bad for their health as well as producing much more waste which can lead to spikes. Feeding twice a day is good but it should be in moderation, only feed them very small amounts - never more than what they can eat in a minute or 2.
Fish will gorge themselves stupid on food in one sitting if we let them because it is instinct for them to do so - in the wild, they don't know when their next meal will be (may not be for weeks) so they will eat as much as they can at once.
Because they are in an environment where they are fed every day, it is our responsibility to not overfeed them. You also need to keep in mind that a fishes stomach is the size of their eye.