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There are between 22,000 and 28,000 species of fish, more than half of all vertebrates. Over 40% of fish species live in surface freshwater which only accounts for .01% of the Earth's total water. |
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The largest living fish is the whale shark, at 60 feet. The smallest fish is a Philippine goby that is about ½ inch long. The largest living bony fish is the mola mola, or ocean sunfish, at 3,000 pounds and 10 feet, but the largest bony fish discovered so far was the Leedsichthys of the Middle Jurassic, at almost 40 feet in length. |
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A "sardine" is any small herring-like saltwater fish. |
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There are three types of fish: jawless (lampreys), cartilaginous (sharks and rays), and bony (all the rest). |
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Most fish are colorblind. |
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A fish that is catadromous hatches and spawns in saltwater but lives its life in fresh, such as eels. The opposite is anadromous, including salmon. |
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Fish have one of four kinds of scales: placoid are toothlike (sharks), ganoid are platelike (gars), cycloid and ctenoid are overlapping (most bony fish). The difference between the last two is that cycloid scales are smooth edged, while ctenoid are rough or comblike. |
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Fish are the only vertebrates with a two-chambered heart. |
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Deep water fish have less bone in relation to flesh; they can therefore endure higher pressures and also are flexible enough to eat a lot at a time during their infrequent meals. |
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Some fish have pharyngeal teeth, which are located in their throats. |
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Fish maintain balance with a pair of calcified nodules called otoliths that roll around inside cavities in their skull. These accumulate layers as the fish grows, thereby giving a good indication of age. |
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The fastest fish are pelagic hunters, like tuna and marlin. They can swim at about 50 mph for short bursts. |
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The lateral line of fish is considered to be a sixth sense and is sensitive to pressure waves and low frequency vibrations. |
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Aquarium fish are the most popular pet in America. |
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Electric eels can discharge as much as 650 volts and can grow to 10 feet long. |
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Because of the difference in saltiness between internal fluids and the water, freshwater fish don't drink but urinate profusely, while saltwater fish do the opposite. The exception seems to be sharks, which have flesh as salty as the water in which they live. |
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Larval flounder start out with eyes on both sides of their heads. Whether they migrate to the left or the right is determined by species. |