When a goldfish dies does it float to the top of water?

Yes. There are two primary reasons why dead fish float to the surface. The first is density. Live fish have a density that closely matches the density of water. This is why they are able to swim relatively effortlessly. However, when a fish dies, its body fills with air and other gasses. This increases the fish's overall density, causing it to become more buoyant and thus float to the surface.

The second reason why dead fish float has to do with rigor mortis. This is the process by which muscles stiffen and shorten after death. When rigor mortis sets in, the fish's body becomes rigid and less flexible. This makes it difficult for the fish to maintain its position in the water and it eventually floats to the surface.