Anglerfish Profile

The angry-looking deep sea anglerfish has a right to be cranky. It is quite possibly the ugliest animal on the planet, and it lives in what is easily Earth's most inhospitable habitat: the lonely, lightless bottom of the sea.

There are more than 200 species of anglerfish, most of which live in the murky depths of the Atlantic and Antarctic oceans, up to a mile below the surface, although some live in shallow, tropical environments. Generally dark gray to dark brown in color, they have huge heads and enormous crescent-shaped mouths filled with sharp, translucent teeth. Some angler fish can be quite large, reaching 3.3 feet (1 meter) in length. Most however are significantly smaller, often less than a foot.

Their most distinctive feature, worn only by females, is a piece of dorsal spine that protrudes above their mouths like a fishing pole—hence their name. Tipped with a lure of luminous flesh this built-in rod baits prey close enough to be snatched. Their mouths are so big and their bodies so pliable, they can actually swallow prey up to twice their own size.

The male, which is significantly smaller than the female, has no need for such an adaptation. In lieu of continually seeking the vast abyss for a female, it has evolved into a permanent parasitic mate. When a young, free-swimming male angler encounters a female, he latches onto her with his sharp teeth. Over time, the male physically fuses with the female, connecting to her skin and bloodstream and losing his eyes and all his internal organs except the testes. A female will carry six or more males on her body.

Giant Barb Profile

Sometimes called the "king of fish," the giant barb has a storied history in its Southeast Asia range. In Vietnam, this distinctive, large-headed species is called cá ho. In Cambodia, the barb appears in ancient temple carvings at Angkor and has been named the national fish.

The giant barb is a river fish that often frequents deep pools but may move seasonally into canals or river floodplains. Juveniles are often seen in swamps or smaller river tributaries.

Though they've been known to reach 660 pounds (300 kilograms), specimens above 220 pounds (100 kilograms) have become exceptionally rare in recent years. These massive fish sustain their bulk on tiny plants such as phytoplankton as well as algae, seaweed, and, during periods of high water, the fruits of submerged terrestrial plants.

Scientists fear that cá ho populations have declined to the point where few survive to reach the age of sexual reproduction. This fish has become severely threatened along its native range, which stretches from Cambodia to the Mekong Delta, because of water pollution, river traffic, and especially overfishing pressures.

The flesh of the giant barb has long been considered a delicacy among residents of the Mekong River Basin, and it is a popular eating and pickling option for the tens of millions of people who depend on the Mekong's aquatic fauna for food.Government programs have focused on captive breeding in an attempt to save this regional icon. Young giant barb can become acclimated to pond life and may be suitable for farming.

Lake Sturgeon Profile

The lake sturgeon, with its sleek shape and rows of bony plates on its sides, looks a bit like an armored torpedo. These freshwater giants have greenish-grey coloring and a pointed snout with two pairs of whiskerlike tactile organs that dangle near its mouth. These organs, called barbels, help it to locate bottom-dwelling prey, such as snails, clams, insect larvae, and fish eggs.

Lake sturgeons can be huge, topping six feet (two meters) long and weighing nearly 200 pounds (90 kilograms). They are also extremely long-lived. Males may live some 55 years, and females can reach 150.

Despite their name, lake sturgeons are also found in rivers, but they avoid salt water. These fish were once a major part of North America's Great Lakes, Hudson Bay, and Mississippi River ecosystems and occurred from Canada to Alabama. But intense fishing has exacted a heavy toll on their populations.

These fish were once killed as a nuisance bycatch because they damaged fishing gear. When their meat and eggs became prized, commercial fishermen targeted them. Between 1879 and 1900, the Great Lakes commercial sturgeon fishery brought in an average of 4 million pounds (1.8 metric tons) per year.

Such unsustainable catch rates were coupled with environmental challenges such as pollution and the construction of dams and other flood control measures. Sturgeons, which return each spring to spawn in the streams and rivers in which they were born, found tributaries blocked and spawning shoals destroyed by silt from agriculture and lumbering.
The 20th century saw drastic drops in sturgeon catches, increased regulations, and the closure of viable fisheries. Currently 19 of the 20 states within the fish's original U.S. range list it as either threatened or endangered.

In recent years, however, the great fish has made something of a comeback. Strong efforts at righting environmental wrongs in the Great Lakes have improved conditions, and concentrated efforts to protect the fish have turned sturgeon into a spotlight species.

Giant Freshwater Stingray Profile

The giant stingray is one of the world's largest freshwater fish, but it's also cloaked in mystery. No one is sure how many giant stingrays are left, which habitats they prefer, or even if they ever venture into the ocean, where their more commonly known relatives dwell.

These ancient fish, little changed over many millions of years, can reach 16.5 feet (5 meters) long and weigh up to 1,320 pounds (600 kilograms). They are brown to gray in color, wide and flat in form, and they sport a long, whiplike tail.

Giant stingrays are known to prowl river systems in Thailand, Borneo, New Guinea, and northern Australia. They often bury themselves in sandy or silted river bottoms and breathe through holes, or spiracles, located on top of their bodies. Stingrays locate prey, usually clams and crabs, with a sensor that can detect an animal's electrical field.

Stingray numbers appear to have dropped dramatically in recent years as their riverine habitats have degraded, and it appears they no longer inhabit some parts of their historical range. Large stingrays have been known to pull boats upstream and even underwater.

Though stingrays do not readily attack humans, they are one of the few megafishes that can pose a real danger to those who handle them. Each ray sports a deadly barb on the base of its tail that can easily penetrate human skin and even bone, much like a hunting arrow. This stinger can be as long as 15 inches (38 centimeters) and typically introduces toxins to the victim's wound.

Chinese Paddlefish Profile

No young Chinese paddlefish have been seen in the wild since 1995, and there have been no sightings of a wild Chinese paddlefish of any size since 2003—leading many to fear that the megafish is already extinct.

Even if evidence surfaces that some paddlefish remain, scientists fear that their numbers are already so low that they will be unable to reproduce successfully.

Chinese paddlefish are thought by many to be the world's largest freshwater fish, with reports of individuals reaching a mind-boggling 23 feet (7 meters) in length and weighing half a ton (450 kilograms). They have long, silver-gray bodies, very large mouths, and a long, wide snout that resembles a paddle. The snouts contain sensors that help them locate the small fish and crustaceans they survive on.

These sleek giants, which the Chinese call sword-billed sturgeons, were once commonly seen and caught in China's Yangtze River. Their enormous bulk and plentiful flesh made them a popular target for fishermen and a welcome addition to dinner tables, including those of ancient Chinese emperors. But the construction of a dam in the 1980s forever altered the Yangtze River habitat of paddlefish and other notable species.

The dam, part of the Gezhouba hydroelectric project, created an impassible barrier between the lower Yangtze River and delta region, where the paddlefish live most of the year, and its spawning grounds in the upper river.

In the years since the Gezhouba Dam was completed, the enormous Three Gorges Dam has further fragmented the Yangtze, and future projects will continue to threaten the paddlefish's habitat.The fate of the critically endangered megafish now likely lies in captive breeding. Such programs have been attempted in the past, but they present many challenges, not the least of which is finding suitable wild adults that have lately proven so elusive.

Arapaima Profile

Also known as the paiche or the pirarucu, the arapaima is an air-breathing fish that plies the rain forest rivers of South America's Amazon Basin and nearby lakes and swamps. One of the world's largest freshwater fish, these giants can reach 9 feet (2.75 meters) long and weigh up to 440 pounds (200 kilograms). They have a wide, scaly, gray body and a tapered head.

Though arapaimas can stay underwater for 10 to 20 minutes, they tend to remain near the water's surface, where they hunt and emerge often to breathe with a distinctive coughing noise. They survive mainly on fish but are known to occasionally grab birds close to the water's surface.

The arapaima's proximity to the water's surface make it vulnerable to human predators, who can easily target them with harpoons. Some indigenous communities consume the arapaima's meat and tongue and collect its large scales, which are fashioned into jewelry and other items.

The Amazon's seasonal floods have become part of the arapaima's reproductive cycle. During low-water months (February to April) arapaimas construct bottom nests and females lay eggs. Young begin to hatch as rising water levels provide them with flood conditions in which to flourish. Adult males play an unusual reproductive role by incubating tens of thousands of eggs in their mouths, guarding them aggressively and moving them when necessary.

While this giant fish's habitat is relatively unmolested, overfishing has become a serious problem, and some South American authorities have attempted to enact protections

Alligator Gar Fish Profile

The prehistoric relatives of this megafish inhabited many parts of the world, but today gars live only in North and Central America.

Of the seven known gar species, the alligator is the largest, reaching up to ten feet (three meters) long and tipping the scales at up to 300 pounds (140 kilograms). These menacing-looking behemoths are generally olive green or yellow and have a heavily scaled body. A tooth-filled mouth and wide, alligator-like snout give the species its name.

These freshwater giants may look fierce, but attacks against people are unknown. They can pose a passive danger, though—the fish's eggs are poisonous to humans if ingested.

Adult gars have few natural predators, although alligators have been known to attack them. Young are preyed upon by larger fish. Alligator gars prey on fish, but they are opportunistic and have been known to feed on everything from waterfowl and small turtles to carrion.

Alligator gars are found throughout much of the coastal U.S. Southeast. They inhabit waters as far west as Texas and Oklahoma, as far north as the Mississippi River Basin and the lower Ohio and Missouri river systems, and southern drainages well into Mexico.

Gars inhabit lakes, bayous, and bays and are able to tolerate brackish and even salt water. But these toothy giants prefer large, slow-moving rivers, particularly those with wide floodplains, where shallow waters provide hatchlings with some protection from predators.

Unfortunately for the alligator gar, flood-control measures such as dams and dikes have dramatically altered their riverine ecosystems and largely eliminated their preferred spawning habitats across North America. These breeding challenges have contributed to significant population declines across much of the animal's range.

Alligator gars are also targeted by both commercial and sport fisheries and have frequently been overfished. They are now protected by law in parts of their range.