Sounds to me like the oscar is possibly sulking, but in a 60 gallon with a convict, it could also be aggression which is intimidating him. Convicts are much nastier than oscars. The big myth with oscars is that they are aggressive, actually they are very gentle, just large waste machines. 60 gallons is not big enough for those fish to stay in long term, not just because of water quality but because of space and territory. For what you have listed here, 90 - 125 gallons should be a minimum.
My oscar is almost 12 yrs old now, and he has gone through times where he also would refuse to eat. One of these times he was sick because my ex didn't do the water changes he was supposed to do. Another time it was because my ex dumped another fish into the tank and there were issues with territory and who got what. If your tank was recently moved, the stress from moving, changing of territory and decoration, and drastic change in water quality could all work in combination to cause the problem you are having now.
Try adding more rocks and silk plants to the tank, move things around and see if that helps. Also, be persistant. Tempt him with his favorite foods. And, honestly, the best thing you could do would be to get them into a much larger tank. Sooner or later those fish won't be able to turn around comfortably in a tank that size because the fish get too big. (oscar and pleco) Even with 100% water changes every day, that oscar and pleco will still have problems eventually because of lack of needed space.
Good call!! It could be he's just sulking from the move (they can be moody & some don't fancy change). Knowing your parameters will allow you to determine if there are water issues you need to correct to make the tank more liveable. Odds are he'll eat in a couple more days but some have been known to go for weeks so don't panic. He won't starve. Just make sure everything else is in order. Increased W/C's (20/25%) are somtimes a stimulant. Garlic Xtreme is often helpful. "T"
