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|Subspecies:||C. a. auratus|
|Carassius auratus auratus
Goldfish (Carassius auratus auratus) are a species of domesticated fish. Goldfish belong to the carp family and were domesticated in China in the Tang Dynasty. They can reach up to 59 cm in size, and 3 kg in weight. This is very rare though, and most goldfish grow to only half that size or less. In captivity, goldfish can live for up to 20 years. In the aquarium, however, most will die earlier because their tank is much too small. Goldfish need a lot of space so they have room to swim and so the water does not get dirty too fast. It is sometimes said that goldfish have very short memories, but scientists have proven that this is not true. One person trained a goldfish to kick a small ball under water and another trained a goldfish to swim through a maze.
Goldfish live best in temperatures between 10 degrees celsius and 30 degrees celsius.
There are many kinds of goldfish. The most common kind is golden-colored, but goldfish come in many different shapes and sizes. Many gold fish have fancy tails. Another common kind is called a black moor, which is black colored.
Goldfish are very sensitive and should not be stroked. Touching them can hurt them and make them sick.
Wild Goldfish are called prussian carp and are silver-green in colour.
Goldfish can get sick. They can have big stomachs filled with liquids (water) or can get spotty because of bad bacteria, and some lose control of swimming because a special organ in their belly, called a swim bladder, gets sick and stops working. However, sick goldfishes can be cured with medicine. Pet shops or veterinarians can help goldfish get better when they are sick. One simple way to help your goldfish if it has indigestion is to feed them peas, as this will help their digestive track work properly.
Nervous System [change]
The most anterior parts of a fish's brain are the olfactory bulbs. These are connected to the two lobes of the cerebrum by stalks. The cerebrum, for the most part involved with the sense of smell. It also seems to control behaviors such as taking care of the young and exploring the environment. The optic lobes process information from the eyes. The cerebellum coordinates body movements and the medulla controls internal organ functions and helps maintains balance. Farther back to the brain is the spinal cord, which is the hollow dorsal nerve cord that characterizes chordates. The spinal cord is protected by the vertebral column. Between each set of vertebrae, a pair of spinal nerves exits the cord and connects to the internal organs and muscles.Most fish have superbly designed sense organs. Chemoreceptors (chemo-means chemical) are located all over the head and much of the body surface. Most fish have ears inside their heads, but they do not hear well. However, a series of pores connected to canals beneath the skin cover the head and the sides of their body. This system, called the lateral line system, detects the motion.
Digestive system [change]
Once food is in the goldfish’s mouth, it’s pushed to the back of the throat where a set of teeth grind and crush it. The ground down food passes down a tube called the oesophagus, which squeezes out excess water. The oesophagus is lined with taste buds and cells that produce mucus to keep things moving on. The oesophagus empties into an expandable section of the goldfish’s digestive which is not to be confused with the stomach. It is simply a buffer zone to hold excess food as needed. Just before this expanded section, chemicals from the gallbladder and pancreas are pumped in with the food. The ones from the gallbladder make up bile, which is used to break down fats; the ones from the pancreas contain enzymes that are used to break down proteins. All along the digestive tract are cells that secrete enzymes that act on carbohydrates, breaking them down into sugars. From the expanded section to the goldfish’s anus, lots of mucus is produced and as much useful material as possible is absorbed into the bloodstream to be used for energy, growth, protection and repair.
Respiratory system [change]
Goldfish get their oxygen from water. As a fish swims, it gulps up water. The water which has oxygen goes through an opening in the fish’s throat that leads to the gills. Gills have many blood vessels within them. Oxygen moves from the water to the blood as the water flows over the gills. The blood vessels gather and store the oxygen that travels over the gills. At the same time, carbon dioxide moves out of the blood and into the water. Now, the water flows out of the slits beneath the gills. These gills are located under the operculum.
Circulatory system [change]
The circulatory system of fish, is responsible for transporting blood and nutrients throughout the body, and blood travels across the body through the network of blood vessels. Unlike humans, fish have single cycle circulation, where the oxygen deprived blood comes to the heart, from where it is pumped to the gills and then circulated to the entire body. The circulatory system of fish consists of a heart, blood and blood vessels. The heart of a fish is a simple muscular structure that is located between the posterior gill arches. In most fish, the heart consists of an atrium, a ventricle, a sac-like thin walled structure known as sinus venosus and a tube, known as bulbus arteriosus. In spite of containing four parts, the heart of a fish is considered two-chambered. The blood contains plasma (the fluid portion of blood) and the blood cells. The red blood cells contain hemoglobin, a protein that facilitates the transport of oxygen to the entire body, while the white blood cells are an indispensable part of the immune system. The thromocytes help in blood clotting. Blood is circulated throughout the body with the help of arteries and veins (blood vessels). The arteries are responsible for carrying oxygenated blood from the heart to the rest of the body, while the veins return deoxygenated blood from the different parts of the body to the heart.
Skeletal and Muscular system [change]
The skeletal system of a goldfish is mainly to protect the goldfish, support its structure and leverage, and helps with its red blood cell production. A goldfish’s skeletal system is made of almost all small bones and cartilage and it barely has any big bones. The bones are made of almost all calcium. There are 3 main muscles in a goldfish’s muscular system, the tail and trunk muscles, the jaw muscles, and the fin muscles. In the tail and trunk muscles, there are myotomes which are muscles blocks and there are myosepta which are connective tissues that separate myotomes. The horizontal septum separates myotomes into two sections, ventral or dorsal. In the jaw muscles, the goldfish uses adductor muscles to close its jaw and abductor muscles to open its jaw. In a gold fish’s fin muscles, there are also adductor and abductor muscles. These muscles move a gold fish’s fins away from and close to its body. There are also erector muscles in the fins that help with the stability and flexibility of the fish’s fins.
Reproductive System [change]
Goldfish reproduce externally. A male will nudge a gravid female goldfish (a female carrying eggs), prompting them to release them onto aquatic plants in the water. When the eggs are on a plant, the male will release a cloud of sperm to fertilize the eggs. A female can release several thousand eggs every spawning period, which is several times every 8–10 days. 
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- Kibria, Farzana. “Homework Help: Science: Biology: Goldfish”. Jishka Homework Help. Jishka Homework Help, 1996-2012. Web. April 17, 2012. <http://www.jiskha.com/science/biology/goldfish.html > web
- "Anatomy and Physiology." SeaWorld/Busch Gardens ANIMALS. SeaWorld. Web. < http://www.seaworld.org/infobooks/BonyFish/anatomy.html >
- Coolidge-Stolz, Elizabeth M.D., et al. Science Explorer; Life Science. Boston, Massachusetts: Prentice Hall, 2007. Textbook.