Last summer, Hitoshi Takeda purchased two goldfish. After a few months, the black one began having trouble swimming properly and spent all of its time lying at the bottom of the tank.
Takeda expected the fish to die, but that time never came. Something was keeping the fish alive and it didn’t take long for Takeda to discover what it was.
As shown in the video, whenever Takeda goes to feed the pair of fish, the orange one begins pushing the black one up to the surface of the water so it can get to the food. It’s not just a single occurance. It happens every feeding.