My Science School

Colourful, tropical creatures with big beaks rather like their feathered namesake – the parrot – parrotfish are known best for two things – eating most of time and pooping. Now, this may seem disgusting, but once you know more about these fish, you will realise that they are saviours of coral reefs. That’s because they spend around 90% of the day eating algae that damage the reefs. This continuous eating cleans the reefs and this ensures the health of the corals.

How does it go about doing this? Each parrotfish has around 1,000 teeth, line up in 15 rows and cemented together to form the beak structure, which they use for biting into the coral. When the teeth wear out, they fall to the ocean floor. But, this does not perturb the parrotfish, because it has so many rows of teeth. These powerful teeth break down bits of coral which are later excreted into nothing but fine white sand that lines the beaches of the South Pacific. This process is known as bioerosion and it helps keep algae under check which provides the right environment for young corals to grow.

You may scoff at the idea that some of the most beautiful beaches in this region are the creation of parrotfish or rather its poop! But, scientists estimate that a single Chlorurus gibbus parrotfish can excrete more than 2,000 pounds of sand each year!

There are about 80-90 species of parrotfish regarded as a family (Scaridae) that live in reefs all around the world, but they all generally live about 5-7 years and grow to 1-4 feet in length. The largest of the family is the bumphead parrotfish found in the Indo-Pacific waters, measuring more than 4 feet and reaching a weight of 100 pounds. Species vary in size from the five-inch Bluelip Parrotfish to the 4 foot Rainbow Parrotfish. Coloring ranges from reds to greens, blues and yellows, as well as grays, browns, and blacks. The parrotfish swims by rowing itself along with its pectoral (side) fins.

They eat and eat all through the day. At night, they sleep in the safety of a cocoon they make out of the mucous they secrete and by finding a suitable hiding place in the coral. It’s nature’s way of keeping them safe from predators.

Like most fish, male parrotfish contains harems of females. This means that in the event of there being no dominant male in a school which may comprise around 30-40 fishes, the largest female changes gender and colour to become the dominant. Once the transformation is complete, they can mate with the other females in the school. Parrotfish release many tiny eggs into the water, which become part of the plankton. The eggs float freely, settling into the coral until hatching.

Unfortunately, humans are their main predators as these fish are considered a delicacy in countries of the South Pacific where they are overfished. And when their numbers are depleted, algae levels shoot up affecting the health of the coral reefs. According to a recent study, reefs where parrotfish were abundant in the 1980s are the ones that are healthy today.

 

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Snakes are really good at playing dead. The West Indian wood snake does a star turn. It is a small boa that when attacked curls itself up tightly. It then releases a liquid from special glands that gives out a rotting smell. To enhance the appearance of decay, it next releases blood into its eyes, turning them a dull, red colour.

The climax of the performance is the blood that the snake lets trickle from its apparently lifeless jaws. This it achieves by breaking open small capillaries in its mouth – called auto-haemorrhaging!

When threatened, a hognose snake will flatten its neck and raise its heads off the ground, cobra0like, and hiss. It may also pretend to strike. If this doesn’t impress the predator, it rolls onto its back and plays dead. The snake emits a foul odour and defecates. It lets its tongue hang out the mouth, sometimes dripping with blood. If rolled the right side up, it will promptly roll back as if to say, “Hey, I am really dead!”

All this time, the snake keeps an eye on the predator waiting for it to look away so that it can escape.

Even newly-hatched hognose snakes instinctively play dead when rats try to eat them.

 

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The animal which has given rise to the idiom is the American opossum. It is renowned for rolling over and collapsing to the ground, drooling. It then remains stock still, with its mouth open and teeth bared, a putrid, corpse-like smell wafts from its anal glands.

From his anal glands, the opossum's body emits green mucus that will discourage most predators from feeding on him while he's in his comatose state. This smell leads the predator to believe that the opossum's body is a rotting carcass. Unfortunately, being run over by vehicles is now the most common way in which opossums are killed -- the smell does nothing to help them in this situation.

While the ability to play dead has probably saved many an opossum's life, it also comes with its own set of risks. If an opossum goes into shock in the middle of the road, it's unlikely drivers will swerve to avoid hitting him because it appears he's already passed on. There are also many opossums who have been buried by people who didn't realize the little marsupial wasn't actually dead. 

 

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Leaf litter frogs of southern Brazil play dead by turning belly-up, shutting their eyes, and throwing back their arms and legs. The frogs stay in their exaggerated death pose for about two minutes.

Fire-bellied toads from Asia and Europe also fake death in dramatic fashion. They arch their backs and contort their limbs to display yellow or orange markings on the soles of their feet. They also flip onto their backs to show similar streaks on their stomachs. It’s a warning to stay away because they are toxic.

It’s thought that the lack of movement caused by thanatosis may focus a predator’s attention on such warning markings, or on foul-smelling odors.

 

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Lemon sharks are rendered harmless when flipped on their backs. These top predators of the sea go limp after about 15 seconds and will play dead long enough for scientists to conduct experiments on them!

The Central American cichlid only pretends to be dead in order to lure unsuspecting prey. It has intricate markings that make it look like a decaying fish. When scavengers come near, the cichlid instantly comes to life and eats the clean-up crew. In Lake Malawi, East Africa, Livingstone’s cichlid sinks to the bottom of lake and lies motionless on its side. Its skin is also blotchy like a carcass!

 

Picture Credit : Google