Take a larger clear plastic freezer bag. Fold over the opening so it'll stay open. Purse string some fishing line around the top of the bag. I actually make tiny holes and run the line thru the bag about 4 times. Tie a simple slip knot in the line.
Lower the bag into the tank. Either anchor it to the bottom with a small piece of LR, or wedge it into a rock opening so it stays put. Turn off pumps and powerheads. Use a turkey baster to squirt some food into the bag.
My guess is the YT is a bit of a food hog. Sit with the string in your hand and wait. Be prepared to watch every other fish in the tank swim into and out of the bag. When the YT swims in, yank the string. It'll close the top around the fish and presto....fish in a bag.