You might be surprised to learn that, no, they don't. At least, not as far as we know. Based on everything we know about goldfish, it is very unlikely that goldfish feel loneliness. It's normal to wonder whether your goldfish will get lonely if kept in a tank on their own.

Do fishes get sad?

According to researchers, fish can get depressed, too, and studies are being done on the aquatic animals in an effort to find treatments for humans suffering from the disorder. ...

Do fish get bored or lonely?

Betta fish are highly territorial, and in the wild, they live solitary lives. Due to this fact, you can see that betta fish don't truly get 'lonely'. Instead of becoming lonely, they may become bored. Signs of boredom, such as frequently hiding, lack of energy, or lack of appetite, can indicate deeper health issues.