Possible Gravel in Stomach.
Can a goldfish swallow a piece of gravel?
I have gotten a piece that was stuck in the mouth. So big that it was wedged in good.
I haven't had the experience of a Goldfish swallowing a piece of gravel, but I have had fish die from gravel getting wedged in their mouths.
Goldfish have rudimentary stomachs at the start of their digestive tracts, so don't really have the ability to store a piece of gravel there. If a piece of gravel was swallowed, it would need to be small enough to pass through the intestines without causing a blockage, otherwise the fish would quickly become distressed and would require surgery to remove it.
The other danger with gravel is the one you mentioned, that of getting gravel wedged in the mouth.
This is quite serious and I have lost several fish because of this. Goldfish seem to be able to stretch their mouths around smooth objects but then can't spit them out.
Gravel in an aquarium or pond must be either too large for your fish to get in their mouths, or small enough for them to spit out.
The trap I fell into, and should have known better, was to forget that Goldfish grow quickly. Gravel that was far too large to fit into their mouths when they were first put into the aquarium, was easily sucked in a few months later.
Goldfish will suffocate if a piece of gravel wedges in the mouth stopping the flow of water across the gills.
If you find a fish in this condition, you have a few options to remove the piece of gravel. The fish will need to be caught in a net to enable it to be held still.
If the gravel is partially sticking out of the mouth, and depending on the size of the fish, use either tweezers or small pliers to pull it out.
Usually this is not the case. Most of the time the fish has got the gravel past its lips and fully into the mouth.
Sometimes you can reach into the mouth with the pliers or tweezers and pull the gravel out. If there isn't room for both to come back out the mouth, the other option is to push the gravel out through a gill.