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Goldfish are probably the most popular pet fish in the world. A goldfish aquarium forms a decorative feature in any room. Unlike other ornaments, however, goldfish do require some care and attention - though they're much more 'low-maintenance' than most other pets. The artificial environment in which they are kept needs to be carefully set up and then needs regular cleaning and water changes to keep the water healthy and allow the fish to breathe.
The first goldfish
All goldfish belong to a single species, Carassius auratus, which originally came from China. Fish breeders in southern China noticed that the drab-colored wild Carp occasionally produced fish with brighter colors, shinier scales or unusual fin shapes. Selective breeding from these natural mutations resulted in various golden forms, and later many other varieties were developed.
Why keep goldfish?
More people in the world keep goldfish than any other pet. These enduringly popular fish are ideal pets for many reasons. They are:
- inexpensive - after the initial costs of setting up an aquarium, goldfish are cheap to maintain.
- beautiful - the Common goldfish is graceful and brightly colored and there are many more 'fancy' varieties, too.
- hardy - Goldfish are the hardiest of aquarium fish, though fancy varieties do have some special requirements.
- low-maintenance - once the aquarium is properly set up, goldfish are easy to care for.
- long-lived - even in a small tank, goldfish can live for around 10 years.
- stress-reducing - fish in a well-maintained aquarium are a joy to watch and provide a great antidote to the stress of modern life.
Basic Biology - how fish work
Although you may be able to describe what a goldfish looks like, many questions may remain about how it functions. What do the fins do? Why is a goldfish gold? Can it hear? Does it need to sleep? A basic understanding of how goldfish live and 'work' can also help you to care for your fish better.
Skin, scales and color
An outermost layer of skin, the epidermis, forms a very fine coating over the fish's scales. The scales are actually transparent and beneath them lies a thin layer of skin containing pigment (color) cells and also a layer of crystalline material called guanine. It is the guanine that creates the characteristic metallic sheen of most goldfish. (Goldfish that have a 'matt' rather than a 'gloss' appearance lack this guanine). The color of the fish depends on the type and combination of pigment cells. White (silver) coloration on a goldfish occurs where there are no pigment cells at all.
How goldfish swim
Powerful muscles down either side of the goldfish's body pull the tail, or caudal fin, from side to side to provide forward movement. The other fins are used as stabilisers, steering paddles and brakes. The dorsal and anal fins stop the body from rolling sideways, while two sets of paired fins - the pectoral and pelvic fins - help with steering and stopping and also prevent the head from pitching up and down.
Fancy goldfish with unusual body shapes or fins may be handicapped in swimming Short-bodied goldfish are low on power, while those with long fins may have steering problems
Breathing and eating
Like all fish, goldfish extract oxygen from the water through their gills. They draw water in through their mouth and it passes out through the gills, inside which threadlike blood vessels near the surface take in oxygen and pass out waste carbon dioxide. If water quality is poor, there will not be enough oxygen for them to breathe.
The gills are also used to create a partial vacuum that enables goldfish to suck up their food. Their mouths are toothless, but they have special teeth located well back in their throats to grind up food as it goes down.
The goldfish's senses
Goldfish are acutely aware of the world around them. Although they do not have external ears, their inner ears can translate underwater vibrations into clear sound. They also pick up pressure waves with their lateral line system, which connects to a series of pits along the flanks. The lateral line allows fish to sense what is happening in their immediate surroundings.
Goldfish eyes are simple in structure but they can focus on near and far objects and they also have color vision. Except in some fancy varieties, eyes are on the sides of the head and move independently of each other.
In the wild, where visibility may be poor, fish rely on taste and touch senses to find their food. Goldfish also use sensory organs to detect chemical signals in the water.
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