Amphibians

Amphibians lay their eggs in water, and young amphibians tend to resemble small fish.

The tadpole, or newborn frog, is born and lives in water. It has a tail that allows it to swim like a fish. It also has gills so that it can breathe under water. As the tadpole grow into a frog, it loses its gills and tail, and develops legs for moving on land. Most amphibians can both walk and swim in water.

source:
http://www.kidport.com /RefLib/Science/Animals/Amphibians.htm

Echinoderms: Starfish and Family

Echinoderms are marine animals that live in the ocean. They have arms or spines that radiate from the center of their body. The central body contains their organs, and their mouth for feeding.

Sea stars, commonly known as the starfish, have 5 or more arms attached to their body.

Sea urchins have many spines connected to their body. These spines help to protect them from predators.

source:
http://www.kidport.com /RefLib/Science/Animals/Echinoderms.htm

Fish

Almost three-forths of the world's surface is covered in water. This water is home to over 20,000 different species of fish. The earliest fossils of fish date back over 400 million years.

There are a wide variety of fish — from the goby which is less than one half an inch long, to the whale shark which can be over 60 feet long.

Most fish breathe through gills. Gills perform the gas exchange between the water and the fish's blood. They allow the fish to breathe oxygen in the water.

Fishes are vertebrates that have a skeleton made of either bone or cartilage. About 95% of fishes have skeletons made of bone. These bony fishes have a swim bladder, a gas-filled sac, that they can inflate or deflate allowing them to float in the water even when not swimming. Fishes with a cartilage skeleton tend to be heavier than water and sink. They must swim to keep afloat. Cartilaginous (cartilage) fish include the ray and the shark.

Most fish swim using a tail fin. Muscles in the tail fin move it from side to side, forcing water backward, and propeling the fish forward. Other fins help the fish change direction and stop. Pectoral fins on their side help them swim up and down. Dorsal and anal fins on the top and bottom keep the fish upright. Pelvic fins on the underside help steer left and right.

Many fish eat plants, while others such as the shark, eat other fish.

source:
http://www.kidport.com/RefLib/Science/Animals/Fish.htm

Mekong Giant Catfish

The world’s largest scaleless freshwater fish lives a tenuous existence in the murky brown waters of Southeast Asia’s Mekong River. Capable of reaching an almost mythical 10 feet (3 meters) in length and 650 pounds (295 kilograms), Mekong giant catfish live mainly in the lower half of the Mekong River system, in Cambodia, Laos, Thailand, and Vietnam.

Once plentiful throughout the Mekong basin, population numbers have dropped by some 95 percent over the past century, and this critically endangered behemoth now teeters on the brink of extinction. Overfishing is the primary culprit in the giant catfish’s decline, but damming of Mekong tributaries, destruction of spawning and breeding grounds, and siltation have taken a huge toll. Some experts think there may only be a few hundred adults left.

Mekong giant catfish have very low-set eyes and are silvery to dark gray on top and whitish to yellow on the bottom. They are toothless herbivores who live off the plants and algae in the river. Juveniles wear the characteristic catfish “whiskers,” called barbels, but these features shrink as they age.

Highly migratory creatures, giant catfish require large stretches of river for their seasonal journeys and specific environmental conditions in their spawning and breeding areas. They are thought to rear primarily in Cambodia.

source:
http://animals.nationalgeographic.com /animals/fish/mekong-giant-catfish.html