Category Nature Science & Wildlife

          Amphibians have different life cycles. Many live mainly on land, but most of them spend at least some of their lives in water. Frogs, toads, newts and salamanders are all amphibians. Frogs and salamanders are able to breathe through their damp skins to a certain extent, both in the water and on land, but toads must rely largely on their lungs and cannot remain in water for long.

          Amphibians! In order for water-dwelling animals to adapt to life on land, many new adaptations had to take place. First, they needed to be able to breathe air instead of obtaining oxygen from water. And fins don’t work well as legs! They needed to be able to move around well on land.

          What group of animals begins its life in the water, but then spends most of its life on land? Amphibians! Amphibians are a group of vertebrates that has adapted to live in both water and on land. Amphibian larvae are born and live in water, and they breathe using gills. The adults live on land for part of the time and breathe both through their skin and with their lungs as their lungs are not sufficient to provide the necessary amount of oxygen.

          There are approximately 6,000 species of amphibians. They have many different body types, physiologies, and habitats, ranging from tropical to subarctic regions. Frogs, toads, salamanders, newts, and caecilians are all types of amphibians.

          Most amphibians live in fresh water, not salt water. Their habitats can include areas close to springs, streams, rivers, lakes, swamps and ponds. They can be found in moist areas in forests, meadows and marshes. Amphibians can be found almost anywhere there is a source of fresh water. Although there are no true saltwater amphibians, a few can live in brackish (slightly salty) water. Some species do not need any water at all, and several species have also adapted to live in drier environments. Most amphibians still need water to lay their eggs.

          A very few fish give birth to live young, but most lay their eggs in the water, which is called spawning. A fish may lay millions of eggs, only a small proportion of which will grow into adults. A few fish, such as salmon and sticklebacks, build nests underwater to protect their eggs. They lay fewer eggs because more young survive. Dogfish and skates protect their eggs in black capsules. The empty capsules are often washed up on the beach, and it is these that are known as “mermaid’s purses”.

          Perhaps you’ve found a “mermaid’s purse” on the beach. Mermaid’s purses blend really well with seaweed, so you may also have walked right by one. Upon further investigation, you can learn more about what they are. The enchantingly named structures are the egg cases of skates and some sharks. This is why they are also known as skate cases.

          While some sharks bear live young, some sharks (and all skates) release their embryos in leathery egg cases that have horns and sometimes long tendrils at each corner. The tendrils allow them to anchor to seaweeds or other substrates. Each egg case contains one embryo. The case is made up of a material that is a combination of collagen and keratin, so a dried egg case feels similar to a fingernail. 

          In some areas, such as in the Bering Sea, skates seem to lay these eggs in nursery areas. Depending on the species and sea conditions, the embryo may take weeks, months or even years to fully develop. When they hatch out of one end, the baby animals look like miniature versions of their skate or shark parents. 

          If you find a mermaid’s purse on the beach or are lucky enough to see a “live” one in the wild or in an aquarium, look closely — if the developing skate or shark is still alive, you may be able to see it wiggling around. You also may be able to see it if you shine a light through one side. The egg cases on the beach are often light and already opened which means the animal inside has already hatched and left the egg case. 

          Mermaid’s purses usually get washed or blown to the high tide line of the beach, and they often get wrapped up in (and blend in well with) seaweeds and shells. As you’re walking along the beach, walk in the area where shells and ocean debris seems to have washed up, and you might be lucky enough to find a mermaid’s purse. You may be more likely to find one after a storm. 

 

          All sharks are carnivorous (meat-eaters), and a few species, such as the white shark, which can grow to 9m (30ft), have been known to attack humans or even boats. But 90% of all shark species are not dangerous to humans at all.

          The United States averages just 16 shark attacks each year and slightly less than one shark-attack fatality every two years. Meanwhile, in the coastal U.S. states alone, lightning strikes and kills more than 41 people each year.

          Each year there are about 50 to 70 confirmed shark attacks and 5 to 15 shark-attack fatalities around the world. The numbers have risen over the past several decades but not because sharks are more aggressive: Humans have simply taken to coastal waters in increasing numbers.

          Over 375 shark species have been identified, but only about a dozen are considered particularly dangerous. Three species are responsible for most human attacks: great white (Carcharodon carcharias), tiger (Galeocerdo cuvier), and bull (Carcharhinus leucas) sharks.

          While sharks kill fewer than 20 people a year, their own numbers suffer greatly at human hands. Between 20 and 100 million sharks die each year due to fishing activity, according to data from the Florida Museum of Natural History’s International Shark Attack File. The organization estimates that some shark populations have plummeted 30 to 50 percent.

          The shortfin mako (Isurus oxyrinchus) is often recognized as the world’s speediest shark. It has been clocked at speeds of up to 20 miles an hour (32 kilometers an hour) and can probably swim even faster than that. Makos are fast enough to catch even the fleetest fish, such as tuna and swordfish.

Picture Credit : Google

          Of course, it is the female seahorse that is the real mother, producing and laying eggs. The difference is that she lays the eggs in a special pouch on the male seahorse’s body. The babies develop inside the pouch and emerge when they are fully developed. As they emerge, it looks as though they are being born from the male seahorse.

          Seahorses and their close relatives the pipefish and the seadragons are very unusual, because it is the males that get pregnant and give birth to the babies. Instead of growing the baby seahorses inside their belly in a uterus, like human mums do, the seahorse dads will carry the babies in a pouch, a bit like a kangaroo’s pouch.

          To produce babies, seahorses have to mate first. Seahorse mating is really beautiful. Males and females dance around one another and flutter their fins, and they may dance together over several days before they actually mate.

          When they’ve decided they like each other, the seahorse females swim towards the surface of the water, and the males follow. The females then put their bright orange eggs into the pouch of the males through the hole at the top of the pouch. Once the eggs are safely inside, the males will add their sperm and shut the opening. The eggs are fertilized by the sperm, and then start developing into baby seahorses.

          With that, the job of the seahorse mum is done! She swims off, and leaves the father to take care of the growing babies. Inside the pouch, the babies grow eyes, tiny snouts, and little tails. It takes about 20 days for the babies to develop, safely tucked away from other animals that might want to eat them.

Picture Credit : Google

          The salmon hatches in freshwater streams and rivers but then begins an incredible journey of up to 5000km (3000 miles), first to the open sea and then to return to the same river in which it was spawned in order to breed. The salmon only makes the journey once —after spawning, it dies. The European eel makes the reverse journey. It spawns in the Sargasso Sea, in the western Atlantic, and its tiny larvae swim to the shores of Europe and North America, becoming lever’s (small eels) on the journey. They then spend several years in freshwater rivers and lakes before returning to the Sargasso Sea to breed. Whales also travel huge distances, this time in search of food. The tiny plankton that they eat is found more abundantly in certain areas during the year.

          Salmon mostly spend their early life in rivers, and then swim out to sea where they live their adult lives and gain most of their body mass. When they have matured, they return to the rivers to spawn. Usually they return with uncanny precision to the natal river where they were born, and even to the very spawning ground of their birth. It is thought that, when they are in the ocean, they use magnetoreception to locate the general position of their natal river, and once close to the river, that they use their sense of smell to home in on the river entrance and even their natal spawning ground.

          A whale shark has made the longest migration journey ever recorded travelling 12,000 miles across the Pacific Ocean. The large fish, named Anne by scientists, was tracked making the mammoth migration from near Panama in the south eastern Pacific, to an area close to the Philippines in the Indo-Pacific. Experts at the Smithsonian Tropical Research Institute followed her signal from Panamanian waters, past Clipperton Island and Costa Rica’s Cocos Island, en-route to Darwin Island in the Galapagos, a site known to attract groups of sharks. The trip was the first recorded evidence of a trans-Pacific migration route for the species of the largest living fish.

          Marine biologist Dr Héctor Guzmán, who first tagged Anne near Coiba Island in Panama, said: “We have very little information about why whale sharks migrate. “Are they searching for food, seeking breeding opportunities or driven by some other impulse?” Genetic studies show that whale sharks across the globe are closely related, suggesting they must travel long distances to mate. An adult female can travel around 40 miles per day and can dive more than 1,900 metres.

          The largest groups of fish are bony fish. Most of these, making up 95% of fish species, are known as teleosts. They have skeletons made of bone and are usually covered with small overlapping bony plates called scales. They also have swim bladders, filled with gas, to help them remain buoyant. Cartilaginous fish include sharks, skates and rays. Their skeletons are made of flexible cartilage but, as they do not have swim bladders, they must keep moving all the time to keep their position in the water. They usually have tough, leathery skins and fleshy fins.

          Bony fish, also known as Osteichthyes, is a group of fish that is characterized by the presence of bone tissue. The majority of the fish in the world belong to this taxonomic order, which consists of 45 orders, 435 families, and around 28,000 species. This class of fish is divided into two subgroups: Actinopterygii (ray-finned) and Sarcopterygii (lobe-finned).

          Cartilaginous fish, also known as Chondrichthyes, is a group of fish that is characterized by the presence of cartilage tissue rather than bone tissue. This class of fish is divided into two subgroups: Elasmobranchii and Holocephali. Common names of cartilaginous fish include sharks, skates, sawfish, rays, and chimaeras.

          The principal difference between bony fish and cartilaginous fish is in the skeleton makeup. As previously mentioned, bony fish have a bone skeleton whereas cartilaginous fish have a skeleton made of cartilage. There are, however, several other differences between these two classes of fish. These differences are listed below.

          The vast majority of cartilaginous fish survive in marine, or saltwater, habitats. These fish can be found throughout the world’s seas and oceans. Bony fish, in contrast, are found in both saltwater and freshwater habitats.

          Fish gills are tissues located on the either side of the throat. These tissues ions and water into the fish’s system, where oxygen from the water and carbon dioxide from the fish are exchanged. In other words, fish gills act as lungs. In bony fish, the gills are covered by an external flap of skin, known as the operculum. In cartilaginous fish, the gills are exposed and not protected by any external skin. The majority of fish, whether bony or cartilaginous, have five pairs of gills.

          Bony and cartilaginous fish are also different in their reproductive behaviors. Bony fish reproduce in what is considered a primitive form of reproduction. These fish produce a large number of small eggs with very little yolk. These eggs are released into the open waters, among rocks on the river or seabed. Male fish then swim over the laid eggs, fertilizing them with sperm which may or may not reach all of the eggs. The eggs hatch into larvae, which are essentially defenseless. The larvae must then develop in the wild, where they are vulnerable to external threats. In this method, the survival rate is low.

          In cartilaginous fish, reproduction occurs internally. The sperm is deposited inside of the female in order to fertilize a small number of large sized eggs with a significant amount of yolk. Cartilaginous fish embryo may develop in one of two manners. In one, the embryo develops within a laid egg, relying on the large yolk for nutrients. In the second, more advanced manner, the embryo are able to develop in the secure and protected environment of the mother’s uterus. These fish are born as fully functional organisms, rather than as developing larvae. After delivery or hatching, baby cartilaginous fish are able to hunt and hide from predators. This development process ensures a higher rate of survival.

          In both classes of fish, the heart is divided into 4 chambers. In the hearts of cartilaginous fish, one of these chambers is known as the conus arteriosus, a special contracting heart muscle. In place of this chamber, bony fish have a bulbous arteriosus, a non-contracting muscle.

          Another difference between the bony and cartilaginous fish is in how each class produces red blood cells. In bony fish, the red blood cells are produced in the bone marrow, the central part of the bone. This process is known as hemopoiesis. Cartilaginous fish lack bone marrow for hemopoiesis. Instead, these fish produce red blood cells in the spleen and thymus organs.