Plugging holes--can it be done?

So the other day I went to have dinner with my boyfriend and his parents--if this situation weren't awkward enough, I noticed that they had a small fish tank (about ~10G) in their dining room, and in it was a large piece of algae-covered driftwood and what looked like a gigantic fantail goldfish. I don't know much about goldfish but, I think that's the name of the type. It had the folded caudal and the pointy dorsal, mostly cream colored with orange spots and it looked like it had mirror scales--like the kind you see on koi. A very pretty fish, but it was huge, bigger than my hand, and barely had any room to swim in that little tank. So I started asking them about their fish, you know the whole "Oh it's so pretty~ I keep fish too, you know~ lalalalala~" song and dance. And it turns out this fish has been through a lot. They used to keep it in one of those whiskey barrel setups outside when it was younger, and on a couple of occasions the filter/agitator actually sprayed all the water out of the barrel and the poor fish survived because the wet roots of the plants kept him wet, the poor thing! It turns out they do have a larger tank for him, a 50G hex. I know this isn't ideal, this is a fish that's supposed to be in a pond. But they seem very attached to this fish, and despite being misinformed, they seem to want the best for him. The main problem is that the tank they have has these huge holes in it for some filtration system it used to have. I drew a diagram lol. Each hole has a little plastic piece around it, but there are no plugs, and nothing that might indicate what was there before.
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Does anyone have any idea whether or not these holes can be plugged or something? I'm stumped.

Could they not attach an external filter via those holes and then put aquarium sealant around the pipes? Not sure about how strong that would be, but I can't think how else the previous filtration would've been attached!

a 50g is good for a fan tail they only need 30 min. there not actuall pond fish they like to be at room temp normal golfish can live below freezing but these wouldnt do to good at that temp. yh all carp can live for hours with no water aslong as there wet. are you sure its a fantail? can you find a pic like it on google because ive never seen a fantail with mirror carp scales. there was proberly some sort of sump of other fillter there before. im not to sure how to block i though

Hi
The best way to seal the holes is to have a piece, or piesce, of glass cut that cover the holes. Make sure the new glass overlaps the holes by at least a couple of inches. Then ensure the glass piece(s) are clean and free of grease. Do the same to the glass inside the tank. Then use aquarium sealant to stick the new glass over the holes. Make sure the sealant goes all the way around around. Leave for at least 24hrs before adding water.

is it glass or plastic if its plastic and you really dont wan the holes or bit of material covering it you might be able to take out the whole pannel of glass and replace that.

I'm pretty sure it's a glass aquarium, but there are plastic pieces that fit into the holes and stick out on either side like the diagram suggests. Will these have to be removed first? I would much rather commit to the small glass circles than replacing a whole panel--seems like if it comes to that it might be better to get a whole new tank.

Its appearance seems pretty consistent with a fantail/ryukin, but it fins aren't as long and flowy as a lot of the pictures. I guess the mirror scales would be an oddity, but it really looks like it has a few, lol. Its a very dull cream/orange except a few shiny scales that look like koi mirror scales.

if it hasnt got the long flowing fins and has mirror skales that would make me think its a koi or mirror carp which like you saed needs a pond if its a koi it can get to 1m long and needs a pond atleats 6 foot by 4 by 6 deep and if its a mirror they even bigger.

....oh great.

The least I can do for this thing is help it get into a bigger tank.. any more advice on the subject is quite welcome.

lol did it look like a koi or mirror ? because ive never see or hear of a fansy with mirror scales. you do mean like the mirrow scales you get on mirror carp the big massive scales right?

I thought it was a kinda weird looking fish too. Usually the goldfish I've seen look really shiny all over, but he's dull with a few big shiny white scales. And definitely ryukin/fantail shape with stubby, rounded fins. I don't know anything about goldfish, but I've seen my fair share of koi, so that's the description that leaped to mind. His parents also said fantail koi, not fantail goldfish, but I didn't think such a thing existed, probably a mistake on their part. If I had to venture a guess right now, I'd say it's just a stubby finned ryukin who happens to have some shiny bits, not some strange koi hybrid.

Could it have been a Ghost Koi?

You can buy after market plugs to plug up the holes, the big tank at my husbands work has that. however the plugs were expensive and hard to get. I would just get a caulk gun of tank silicon and two thick glass or plexi bits. clean both well and use a great gobbing amount of silicon. I fixed a crank in a tank at home and it worked well.

sounds like a koi or carp to me do you think you can get a pic?
when you say cream colour do you mean like a creamy brown like a normal carp or more of a white cream like a ghost?