Photograph courtesy Zeb Hogan
Giant freshwater fish from around the world clock in as 2011's most popular environment gallery on nationalgeographic.com. Increasingly rare because of fishing, pollution, and loss of habitat due to human activity, these so-called megafishes can be indicator species of aquatic ecoystems.
National Geographic Explorer Zeb Hogan has wrangled, photographed, and studied many of these freshwater monsters. Some, like the Chinese sturgeon, are "living fossils" that have changed little over millions of years.
Pictured is an arapaima fish at an aquarium in Manaus, Brazil. This South American giant can reach lengths of more than 10 feet (3 meters) and weigh upwards of 400 pounds (180 kilograms).
Like several megafish species in our gallery, the arapaima is the focus of conservation projects, which may be racing against time to save these animals in the wild.
2. Colossal Sea Creatures
Photograph by Paul Nicklen, National Geographic
Although megafish are impressive, even bigger organisms ply the world's oceans, from the great whales to sprawling jellyfish. A powerful stinger, the lion's mane jellyfish (pictured) can reach a diameter of 6.6 feet (2 meters), with tentacles topping 49 feet (15 meters).
The world's biggest fish, the whale shark, can reach lengths of 40 feet (12 meters). The world's biggest mammal, the blue whale, can easily reach the length of a city bus and weigh close to 200 tons.
Also tipping the scales are giant clams, which can weigh more than 500 pounds (227 kilograms) and live for more than a hundred years.
Photograph by John Stanmeyer, National Geographic
Humanity has long been fascinated with volcanoes, working them into myths and legends in many cultures. Photographing nature's awesome power is no easy task and can be dangerous.
Mount Semeru, seen with an ash plume, is the highest volcano on the Indonesian island of Java, where it is surrounded by the smaller volcanoes Mount Bromo and Mount Batok. Mount Semeru has been in a constant state of eruption since 1967.
Other volcanoes have also put on recent shows, from the Big Island of Hawaii to Mount Etna in Italy and boiling mud pools in Ethiopia.
4. Deep-Sea Creatures
Photograph by Awashima Marine Park, Getty Images
Not surprisingly, human beings have rarely encountered the animals that dwell in the world's deep oceans in total darkness and under intense pressure. But recent expeditions, often with the aid of robots, have give us a new glimpse into the watery depths. It turns out that the adaptions that have allowed such species to thrive there make them resemble the stuff of our nightmares.
Considered living fossils, frilled sharks normally live at depths up to 5,000 feet (1,500 meters). This 5.3-foot (1.6-meter) specimen was found in shallow water in Japan in 2007, though like many deep-sea creatures, it died shortly after finding its way to the surface.
A species with an even more terrifying appearance, the fangtooth fish, has been found at depths near 16,500 feet (5,000 meters).
Photograph by Carsten Peter, National Geographic
Tornadoes can be devastating, potent reminders of the awesome power of nature.
In this photo, a rare "mother ship" cloud formation is seen over Childress, Texas. This is a sign of a supercell thunderstorm, a type of storm that often kicks off tornadoes with winds exceeding 200 miles an hour (322 kilometers an hour).
Tornadoes can form over wide swaths of land and sea.
6. Spring Landscapes
Photograph by Eugenijus Zvergzdys, My Shot
Most living things are tied into the rhythm of the seasons, whether they live in the Northern or Southern Hemisphere or even right on the equator, where cyles of moisture tend to dominate more than insolation.
Spring, of course, is a time of rebirth and rapid growth, as this placid scene at the Chicago Botanical Garden suggests. Spring brings a dizzing assortment of flowers and active animals, each filling its own ecological niche.
(See the spring landscapes gallery.)
Photograph by DigitalGlobe/Getty Images
From Japan to Sri Lanka and Chile, tsunamis have wreaked havoc in the past few years, leaving a staggering toll of death and destruction in their frothy wake.
Seismic studies have helped scientists get better at predicting their arrival, although tsunami warning systems are still lacking in many parts of the world.
Pictured are waters retreating from the coast of Sri Lanka after the 2004 tsunami, which had been triggered by a 9.0-magnitude earthquake off Indonesia and the Indian Andaman Islands.
Photograph by Mark Tipple, My Shot
Summer is often a time of plenty for wildlife and people alike. Fireflies decorate the skies, bees buzz on flowers, and fresh watermelon is sliced.
Here, two swimmers play in the storied waves of Bronte Beach off Sydney, Australia.
(See the summer gallery.)
9. Dangerous Sea Creatures
Photograph by Paul Nicklen
They may be beautiful, but these sea creatures can be deadly.
It may look harmless enough, but the striped surgeonfish of the Indo-Pacific sports a venomous spine. Scientists estimate that 50,000 people are injured a year from contact with the world's 1,200 species of venomous fish. The poisons are also being investigated for use in new drugs.
Other sea creatures that can pack a punch include the stinging yellow sea anemone, "flying" needlefish that become airborne daggers, and, of course, great white sharks.
10. Colorful Sea Creatures
Photograph by Jens Troeger, My Shot
As divers and snorkelers well know, the oceans are filled with creatures that come in a bewildering array of colors. This includes intricate patterns, camouflage, and even varying degrees of transparency.
Pictured is a white sea anemone and a sea star in the waters off British Columbia. Other colorful favorites include clown fish, angelfish, and mantis shrimp.
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From the fearsome piranha to the mighty anaconda, see some of the world's most terrifying aquatic species.
See the stingers, shockers, and other amazing abilities of the flattened fish that have gracefully cruised Earth’s seas for 150 million years.
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