Here's is an article from a GG blog on the subject....
My Giant Gourami Is Not Eating, What to do?
Good question,
Some owners sometimes encounter this problem, and in this post I'm going to clear things up for you.
1st of all, why did this condition alarm you, well its simply because usually your Giant Gourami would devour and eat like a crazy hungry fish and when suddenly he stops eating......of course you're worried.
The first thing to do is check the water quality, although the Giant Gourami is an EXTREMELY HARDY FISH...if the water is close to toxic muck....don't expect your Giant to thrive in there.
- Recall when you last made a water change, was is long time ago?...if yes change 50% of the water and replace with de-chlorinated water (use the water conditioner/de-chlorinator)
- If you recently made a water change and he's not feeding.....then check whether you added de-chlorinator...if not quick and add the de-chlorinator!
- If you think nothing is wrong with the water then, this is what this article is about....continue reading....
Ok, if you are absolutely sure that the water is absolutely ok, then this must be nature's course in action.
In the wild, during the monsoon season water levels in rivers and lakes rise and many vegetation drown and feeder fish/shrimp disperse in a larger than usual body of water, sometimes carried away in the monsoon flood. What happens is, the Giant Gourami fails to get food and through the period remains alive without food. This natural phenomena although cruel has a good effect, it gives time for the Giant Gourami (and other fish) to rest their intestine and stomach (gastrointestinal system). They will defecate as the final remaining food is digested and eventually remain without any food at all. This gives time for its intestine to heal and grow and prepare for when food is available - in the aquarium the Giant might take small bites but never finish the portion you give.
When the monsoon is over and water levels return to normal and the now well fertilized soil(due to rotted matter) allows vegetation to bloom, food supply increases exponentially for the Giant.
The Giant Gourami will then resume its heavy eating diet and starts to put on body mass.
In the aquarium or pond setting(I don't like to use the word "captivity")...this natural phenomena does not occur and the biological drive of the Giant will cause it to stop eating at any time(not according to the monsoon season which usually takes place between early October to the end of December) for the benefit of its intestine and stomach.
So what do you do?
Simple, don't feed your Giant. Leave it for 7 days at least(you can go up to a month but you will notice your Giant losing body mass, so 7 days is better)...feed nothing he will beg for food just ignore, if you at anytime break this 7 day period of "fasting" his intestines will not have healed and he will restart "fasting" any another period of time and you'll have to do it all over, don't feed him for 7 days.
If you have other fish in your tank(read my other post on how to trick the Giant into accepting tank mates), they can enjoy the benefit of healed intestine, boosted immunity, and increased activity after the 7 days. So bottom line, when your Giant goes into the "monsoon fasting phase"(although its not exactly monsoon in your aquarium or pond) stop feeding all your fish for 7 days. Resume feeding on the 8th day.
You can use this time to clean the tank, resupply food stock and just watch your Giant interacting with other mates in the aquarium.
I hope I've answered your question, I included solid proof from nature itself in the hopes that your Giant will live to its best.
All the best and WE LOVE GIANT GOURAMIS!!!!