Although koi fish may appear to be large goldfish, the two are actually distant cousins, with koi being more closely related to carp.
If your fish is looking a little overweight/fat, it could be caused by a number of different things, and not just that he’s eating too much.
Feed your fish diets specifically formulated for their type and beware of toxins.
Just like humans, fish often have to cope with stress and its complications.
All living things, including your aquarium fish, are subject to disease organisms and parasites.