I have a cute chubby goldfish that had two siblings in amongst the regular goldfish. Unlike last year, something has killed 80% of the goldfish in our pond. I decided to take out the cute goldfish and put it in a large glass vase which I keep water bamboo. (My fighting fish lives in one of these very successfully). The goldfish is frequently up at the top of the water as if it is trying to get air. He is fed. What could be the problem. Water is chlorine free.

If there is no air system for the vase, then all he is doing is trying to breathe I would suspect.

This is not a disagree, this is you failing to provide air and the proper care for your fish.

Beta fighting fish breath with an organ called a labyrinth which
Is comparable to our lungs. They breath by surfacing to the top of the water to take a breath of air. This is how it is possible for them to live in vases.

A goldfish gets it's oxygen from within the water through it's gills.
In order for the goldfish to get the amount of oxygen it needs, an air supply must be given to the water.
Goldfish also produce a lot of ammonia which cause the unfiltered water of a vase to become so polluted that it will definitely cause death.

Trying to figure out the problem with the pond water is the best solution for the fish.

Thanks, I appreciate my mistake and won't run into this problem in the fall when I have to bring the goldfish in. I thought goldfish and fighters both survived in a fish bowl.

Goldfish are about the nastiest fish you can keep in a fishbowl or aquaruim due to the incredible quantites of ammonia they output. I think it must a ratio something like 1/2 oz of food to 10 gallons of pure ammonia but I'm sure it just seems that way. They can cr*P up and pollute a nice-sized aquarium with filtration and aeration in what seems to be nothing flat so having them in a still-water bowl really exacerbates the problem.
Anytime you see fish coming up to the top of the water to take in air, ('cepting that labyrinth fish thang you was writing about earlier) you know you've got a water quality issue and should be doing a partial water change and figuring out if you have too many fish for the tank size or something died and is polluting the water or your filters or biofiltration beds are overloaded. Whatever the cause, you don't have a lot of time to waste before you start holding burial at sea ceremonies in your bathroom...

Get some nice Gold Swordtails or the like instead - much cleaner fish...

You didn't give many pond details so I don't know if the water was getting too hot for the fish, lack of shade, overfeeding or simply overcrowding is the cause of you losing 80% of your fish pop. Even though its an outdoor pond, seems a lot of folks around Dallas will add a pump help aerate the water to help the temps and breakdown of waste products...