Does anyone have any suggestions on what could be happening with my oscar?
It has been 3 1/2 weeks since our oscar last ate.
He seems perfectly healthy and we have tested his water a couple of times a week to make sure that we could rule that out.
He has been displayin odd behaviour but there has been nothing unusual about his environment that has changed that could explain it.
He is about a year old and about 16cm long.

Please help!

What size tank do you have him in? Does he have any tankmates? He could be lonely or simply bored. I know it worries you that he hasn't eaten in so long but he'll be ok. Try different foods, veggies and stuff. There is a link on the homepage about things to feed them and a thread here with what the members feed theirs. I just found out that mine love watermelon and onions. Try lettuce and cucumbers.
I hope this helps.

? you did'nt say temp of the tank. O's digestion functions better in the upper 70's to 80 degrees. Is the thermometer at the right temp? my O is always playing around the top of my submersible. post your readings for amon, nitirite, ph, nitrate.

are his scales sticking out it could be dropse if so there is no hope for him

My oscar once went a whole month with out eating just because I moved things around to different places in the tank. They are moody sons of guns. but as long as your water temps and readings are ok and the oscar seems to look fine(no signs of illness) then sooner or later he will eat....

Not that this will make it any easier for you, but a lot of us have been in this position. Sometimes Oscars do stop eating for no reason at all. Well, there must be a reason, we just don't know why.

Could you please test the water and give us the results?

Also, is the fish breathing heavily at all?

I would be inclined to hold up trying to feed him for a couple of days. Try it again and see if the Oscar wants to eat. You could also try feeding live food. See if your shop has in live shrimp. Failing this, try some live crickets and see if this triggers the Oscar into feeding. Please don't feed them any shop bought live fish.

My oscar is not very hungry lately, but his mealworms that he didn't eat turned to beetles and now he snacks some of those.Or some larvae.
This morning he was taking some Sera Vipagran, which I was feeding mu vieja and silver dollars.
Stupid fish.but just not hungry at the moment!