Internal Organs
- The gas bladder, or swim bladder, is an internal organ that contributes to the ability of a fish to control its buoyancy, and thus to stay at the current water depth, ascend, or descend without having to waste energy in swimming. The bladder is only found in the bony fishes. In the more primitive groups like some minnows, bichirs and lungfish, the bladder is open to the esophagus and double as a lung. It is often absent in fast swimming fishes such as the tuna and mackerel families. The condition of a bladder open to the esophagus is called physostome, the closed condition physoclist. In the latter, the gas content of the bladder is controlled through a rete mirabilis, a network of blood vessels effecting gas exchange between the bladder an the blood.
- Certain groups of fish have modifications to allow them to hear, such as the Weberian apparatus of Ostariophysians.
- The gills, located under the operculum, are a respiratory organ for the extraction of oxygen from water and for the excretion of carbon dioxide. They are not usually visible, but can be seen in some species, such as the frilled shark.
- The labyrinth organ of Anabantoidei and Clariidae is used to allow the fish to extract oxygen from the air.
- Gill rakers are bony or cartilaginous, finger-like projections off the gill arch which function in filter-feeders in retaining prey.
- Electric fish are able to produce electric fields by modified muscles in their body.
- Many fish species are hermaphrodites. Synchronous hermaphrodites possess both ovaries and testes at the same time. Sequential hermaphrodites have both types of tissue in their gonads, with one type being predominant while the fish belongs to the corresponding gender.
- The blood circulation of fishes is called "single circuit circulatory system."
Read more about this topic: Fish Anatomy
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