If you want to know how add fish to the garden pond in Zelda TOTK or the Tears of the Kingdom (aka the pond at Link’s house), you’ve come to the right place. I’m afraid I don’t have much good news, but it’s still worth knowing how the system works. If for no other reason, then to avoid putting yourself in a situation. Let’s get into it.

How to add fish to a garden pond in Zelda Tears of the Kingdom
To add fish to the garden pond in Link’s house in Zelda Tears of the Kingdom you need to create one first. Talk to Granteson and have him make you a garden pond. It will set you back three hundred rupees, which isn’t too bad. When the pond is ready, one Sanke carp will be swimming in it. It always respawns, so if you really have no other choice, you can eat it. It won’t do you much good, but it’s there. So you might think that all you have to do is go and catch a fish and then throw it in the pond, right? No, of course not. A fish dies when you take it out of the water, don’t you know?
According to a Reddit user TheRealSgreninja, the only way to add fish to the pond in Link’s home garden in Zelda Tears of the Kingdom is to scan the Mipha Breath of the Wild amiibo. You have to scan it while standing right above the body of water. This will cause a bunch of live fish to spawn there. The problem is that they disappear after a while, just like if you scanned an amiibo elsewhere. So, yes. No matter what you do, the Sanke carp is the only aquatic pet you can keep indefinitely. Will this change with a future update? May be. However, as it stands now, you’re either using the Mipha amiibo for some sort of temporary company, or you’re just littering the pond with dead fish.