Need advice on "preserving" a goldfish

[Kneedles]

I recently found out that I have only one goldfish left in my small pond, which is quite saddening, despite the fact that I have never paid much attention to them. I decided to catch it, and I have been keeping it in a tank that contains water and pond weed that comes directly from the pond that it was in.
What should I do with it? Its mouth is too small for it to be able to eat any of the food that I have been giving it, and it does not seem to be very active. Thanks in advance for any help.

 

[Chickerdoodle13]

Do you have a filter on the tank? I would definitely get a filter that is more than the amount the tank actually holds. That could be a reason for it's sluggishness. Ammonia buildup and lack of oxygen cause listlessness.

You can also try goldfish flakes instead. They are super cheap at stores like walmart and will be easier for a small goldfish to eat. Otherwise, if you have the larger pellet food, just put it in a baggy and mash it up with a mallet or hammer and then try that.

Best of luck! I hope he pulls through.