Ichthius
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Joined: 23 Nov 2007
Posts: 32
Location: North Carolina, USA
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 Posted: Sun Nov 25, 2007 8:38 pm Post subject: Fish Anatomy: Internal and External (Glossary) |
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Fish Anatomy
This article intends to cover the general external and internal anatomy of fish. Since the information and pictures provided were originally collected from a fishery site, I have tried to reorganize and adjust the information to target the fish keeping hobby. Credit for the source of the pictures is given to: http://myfwc.com/Fishing/Fishes/anatomy.html#internal
Why is it Necessary to Understand Fish Anatomy?
As fish hobbyist who aim to keep healthy aquariums and fish, a basic understanding of their anatomy and physiology is necessary. We often find ourselves stumped by or battling with a disorder or disease in our home aquariums. By understanding the anatomy of our fish, it is possible to grasp a better understanding of what has become compromised in the fish itself.
The following is a list of the primary organs, their functions, and possible malfunctions.
Brain
The brain, as in any animal, serves as the control center of the fish’s body. It receives and interprets signals from other parts of the body. It “tells” the rest of the body what to do and serves in the functioning of the nervous system; pain reception, homeostasis (the healthy balance the fish must maintain), and decision making.
Gills
The gills aid in respiratory functions. Many problems may occur with the gills; rust (a red dusty appearance, usually occurs on betas), Ich attached inside the gills, etc. One can also observe the gill beats. Much like observing the heart beat of humans, it’s possible to watch for the amount the gill beats within one minute. An increased gill beat means that the fish is struggling to breath or is under stress.
Gonads – The Reproductive Organs
Understanding the reproductive system of fish is necessary for successful breeding and sexing of fish. Cases where this information would be necessary are situations like sexing young livebearer fry for separation, determining whether or not a female livebearer is pregnant and soon to give birth (by observing the appearance of the vent-gravid spot). Male livebearers are easily distinguished from females in that their fins located near the vent, when mature, develop into a gonopodium (aids in the transfer of sperm to the female during reproduction).
In the rearing of livebearers in overstocked or poorly kept aquaria, the reproductive organs may be ambiguous, difficult to sex-hermaphroditic, in young fry. This problem is often encountered by newer hobbyist wishing to breed their fish or in small tanks becoming overpopulated.
Heart
The heart is part of the circulatory system; this system transports nutrients and oxygen to other parts of the body and transports waste products for removal. Some of these waste products are carried to the kidneys and removed from there.
Kidneys
As previously stated, the kidneys aid in the removal of waste from the blood. The kidneys also aids in regulating the liquid and salt content of the fish’s body. This regulation is how different fish are able to live in fresh, brackish, or saltwater aquariums. Some fish, like mollies, are able to adapt to different salt contents in water, e.g. brackish fish living in freshwater. However, as a rule, fish do better in the type of water they came from; saltwater fish in saltwater, freshwater fish in freshwater, and so on. The kidneys are one of the organs affected by the disease Dropsy, which causes the organs to expand within the fish’s body increasing pressure and causing bloating.
Lateral Line
The lateral line helps fish to maintain equilibrium, balance. It also detects vibrations in the water, sort of like hearing. In some cases, a fish’s lateral line can become damaged or diseased. Head and lateral line erosion (Hole in head disease, lateral line disease, etc) are when these areas begin to deteriorate slowly. This inhibits the swimming and balancing abilities of the fish.
Liver
The liver, like the kidney, allows for the removal of waste products. It filters, in a sense, materials entering the blood and allows for nutrients to enter the blood. One of the waste products that it aids in removing is nitrogen, familiar to the aquarium chemistry.
Muscles
Fish muscles, like the muscle tissue in other animals, help the fish to move. They also store essential materials and hold the fish together, in essence. The muscles are the meat of the fish and are generally what becomes infected and deteriorates when problems arise. One can imagine that when this tissue is attacked by a disorder, the normal functioning of the fish is at risk.
Spine
The spine of the fish runs horizontally from the base of the fish’s head to the tail fin. The spine provides support and a center point for the rest of the body. The spinal cord, within the spine, is part of the nervous system. When the spine is damaged, either from birth defect or disease, such as Tuberculosis, the nervous system becomes compromised. In addition, the fish becomes deformed and such an injury may lead to paralyzation or death.
Stomach and Intestines
The intestines and stomach are part of the digestive system. Food matter is digested and passes through them until exiting the body of the fish. Fish may contract intestinal parasites that inhibit the fish’s ability to digest and use the nutrient foods the fish needs. Another problem that may occur is a blockage or constipation. The undigested food and waste begins to build up in the intestines and press against other vital organs; Example: the swim bladder. This can lead to a Swim Bladder Disorder (SBD), which could lead to death if the fish is unable to eat and swim properly.
Swim Bladder
The swim bladder is a vital organ in the fish anatomy. Basically, the swim bladder is an air filled organ that allows the fish to swim normally and maintain balance. The pressure within the organ and from the outside water changes depending on the depth of the water. This allows the fish to sink or float as necessary. If the organ is compromised, whether it be deformity, infection, trauma, or constipation, the fish loses its balance and begins to have difficulty swimming. Swim bladder disorders, depending on severity, can lead to death. This problem must be corrected.
Vent
The final part of the fish’s anatomy relevant to the fish hobby, is the vent. Briefly touched on earlier, the vent generally refers to the anus of the fish where waste is removed from the body. The term vent may also be applied to the end of the birthing canal in female livebearers.
Hopefully this detailed glossary of terms helps you in understanding the fish you keep and with any problems that may arise. Please refer to the Disease section for further information on diseases that may affect these areas.
Images of the External and Internal Fish Anatomy
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