Hardtail Moray Eel (Anarchias galapagensis)

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Excluding chondrosteans, lobe-finned fishes (lungfish and coelacanths), and non-teleost neopterygians (gar and the bowfin), all bony fishes (Osteichthyes) are classified as teleosts. They are the major lineage of neopterygians and shortly after their initial evolution, the diversity within this group of fish exploded, foreshadowing the immense diversity of fish that now exists. Pictured is the anatomy of a yellow perch (Perca flavescens), a common North American freshwater fish.

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Evolving directly from the earliest ray-finned fishes are the chondrosteans. The most primitive of all ray-finned fishes, chondrosteans have skeletons made of both cartilage and bone. Living members include sturgeons, paddlefishes, and bichir. Pictured are three extinct chondrosteans and a bichir, with their respective genus names listed.

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Electric eels (Electrophorus electricus) are not actually eels at all. They are giant-sized members of the knifefish order. When fully grown, these fish can be as large as a foot in diameter and 2.5 m in length. It has no dorsal fins, but one long fin that runs along the ventral side of its body. Their eyesight is quite poor, so they rely on producing weak electrical pulses to sense the environment around them. Electric eels are also capable of producing bursts of up to 600 volts, which is powerful enough to kill surrounding fishes and potentially even humans that might be near them.

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Although the individual pictured is only a fingerling, milkfish (Chanos chanos) can grow to be 6 ft in length. They are large, fast-moving filter feeders that tolerate a wide range of salinities, but generally prefer freshwater. They are catadromous, meaning they swim out to sea to spawn, but spend the majority of their lives upstream in fresh or brackish water.

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Native to western Africa and commonly found in still, murky, muddy waters of rivers, lakes, and swamps, the elephantnose fish (Gnathosomus petersii) possesses a weak electrical system that functions as a kind of radar to detect obstacles, food, and mates. The highly mobile, finger-like appendage on its chin is used for probing the muddy bottom in search of food. The elephantnose has an unusually large brain that, in relation to body mass, is equaled only by that of humans. Perhaps for this reason, it has a remarkable ability to learn and its playful personality makes it a popular aquarium fish.

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The Indonesian coelacanth (Latimeria menadoensis) was discovered very recently (late 1990s), and as such there is not a lot of information regarding its behavior or ecology. However, because it is physically extremely similar to the coelacanth (Latimeria chalumnae) found off the coast of South Africa (discovered in the 1938), scientists can assume the two fish have similar life habits. Genetic analysis has revealed that the two species diverged from one another around 5 million years ago, effectively making both species of coelacanth living fossils.

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The West African lungfish (Protopterus annectens) is the largest of the four lungfish species found in Africa, reaching lengths of up to 2 m. Rather than gills, it has a pair of lungs that it uses to obtain oxygen. When the dry season comes, this fish makes a mucous-filled cocoon for itself and burrows into the mud to keep its skin hydrated.

Photo by Jibran Shariff

Common carp (Cyprinus carpio) are bottom feeders that are not known for being particularly beautiful. Growing up to 1.2 m in length and weighing as much as 37 kg, these fish can be big, ugly muck-dwellers.
However, selective breeding has come up with some very beautiful varieties of Cyprinus carpio. Koi fish, or nishikigoi, are bred for their beautiful, bright colors and often kept in privately owned ponds for their aesthetic value.

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The beaked sandfish (Gonorhynchus gonorhynchus) is adapted to spend its days in the substrate on the seabed, hiding in the sand or mud. They leave the safety of their hiding places at night to feed on invertebrates that live on the seabed. Because they lack teeth, their mouths are surrounded by papillae (sensory flaps) that help it to find food. As the second photo depicts, they have excellent camouflage that allows them to blend in almost perfectly with the sand along the ocean floor, which has benefits for hunting down prey and for avoiding predators.

(Photos © RyanPhotographic)