How to Classify Goldfish

Color

The coloration of a goldfish, or any fish for that matter, depends on a wide variety of circumstances. Water composition and temperature greatly affect a fish's chromatophores (pigment cells), as do diet and environment there are two types of chromatophores: melanophores and xanthophores. Orange goldfish exhibit an abundance of xanthophores and an absence of melanophores, while the blue or black varieties, such as a Black Moor, have an abundance of melanophores and lack xanthophores.

Swim Bladder

A swim bladder is a gas-filled sac that helps a goldfish rise or fall in its watery environment. In a goldfish, there are actually two swim bladders, one directly in front of the other. These compartments contain oxygen, carbon dioxide and nitrogen.

By inflating the swim bladder the goldfish rises; conversely, when the goldfish deflates the swim bladder, descent is made easier. This also helps the fish stabilize and hover comfortably. Some of the more elaborate varieties are top-heavy, and as a result, will always swim at an angle. An example of this is the Lion head, which has a smaller forward sac, causing its head to thrust slightly at a downward angle.

The swim bladders are more notorious for the ailment it causes—swim bladder disease. Afflicted fish swim on their sides at the top, or conversely, sink to the bottom. Some also lose their sense of balance and might somersault as they attempt to swim forward. This is sometimes caused by changes in temperature that most often occur in fish transportation. Swim bladder disease is a digestive problem. Detected and diagnosed early, it is treatable by isolation and medicated food. However, it is not a contagious disease. Detected too late, the results are irreversible—it is a deadly disease.

Other Organs

Although goldfish are different from tropical fishes in terms of anatomy, they possess circulatory, respiratory, digestive and nervous systems common to most members of this vertebrate group.