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Related Science: Ichthyology

The Fish Corner: An Icky…What?

Although a marine biologist studies many aspects of marine life, including fishes, it is an ichthyologist whose job is to study fishes. Ichthyologists (pronounced: ick-the-OL-oh-gist) conduct scientific research around the world to learn more about growth rates, reproduction and migration of fish. With this information, they can help state and local governments make responsible management decisions for our ocean’s future.

How old is that trout?

Did you know that ichthyologists can determine the age of a fish by reading rings on small bones located in the fish’s head? In the same way that trees make rings that mark the passage of time, fishes deposit small rings every year on their ear bones or “otoliths”. By counting the rings under a microscope, ichthyologists can determine the fish’s age. Knowing their age helps scientists understand how long the fishes can live and how quickly they grow. Although our knowledge of longevity is still developing, scientists know that fishes live from a few weeks or months (some of the small reef fishes) to 50 years or more (sturgeons and rockfish).

Can fishes smell and taste?

Yes! Most fishes have two nostrils located on top of their heads that help them smell. Of all the species of fish, sharks, rays and eels have the most highly developed sense of smell and it is believed that some species of sharks can smell the equivalent of one drop of blood in an Olympic size swimming pool. Fishes also have a keen sense of taste due to the many taste buds lining the inside of their mouths.

Do fishes drink?

Although most fishes do drink water, the old expression to “drink like a fish” may be a bit of a misnomer. Although marine fishes must drink in order to avoid dehydration, fresh water fishes obtain the water they need to survive not through drinking, but by osmosis.
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Do fishes sleep?

Because most fishes don’t have eyelids (sharks being the exception), fishes don’t sleep in the way that humans do. Many fishes do engage in a resting period by floating in place, wedging themselves into the sand or coral or even, like a parrotfish, by building a mucous cocoon. While “sleeping” fishes must still be aware of their surroundings or risk becoming another creature’s meal!

How many different types of fishes are there?

Although scientists are constantly discovering new species of fishes, the most often quoted estimate is about 20,000.

How fast can fishes swim?

Seahorses are the slowest moving fishes in the ocean. At top speed it would take a seahorse about 2.5 days to travel about a kilometer (.6 of a mile). The bluefin tuna is the fastest fish in the ocean, reaching speeds of up to 100kph (62 mph) over short bursts. Other ocean racers include the swordfish, marlin, wahoo and the blue shark.

How good is a fish’s eyesight?

Scientists believe fishes actually have excellent eyesight, comparable to humans, with some actually being able to see in color. Fishes also have a number of specialized eye adaptations that enable them to see clearly underwater.

How do fishes breathe?

Unlike marine mammals such as whales and dolphins with lungs that store oxygen from the surface air, fishes have gills. Gills are a series of membranes located on each side of the fish that function as respiratory organs. As water passes over this system of extremely fine gill membranes, the fishes absorb the oxygen from the water. The gills contain a network of fine blood vessels (capillaries) that take up the oxygen and diffuse it through the membranes. When fishes are taken out of water, they suffocate, because their gills collapse and they are unable to absorb oxygen.

How do schools of fish move together?

Fishes can’t hire choreographers to coordinate their perfectly timed movements, so how do they manage to move in sync with each other so beautifully? The secret is a collection of tiny hair cells that are grouped along a line running across the body of a fish (the “lateral line”). These special sensory hairs pick up the same information from the water and each fish responds to it in exactly the same way. The result is a perfectly timed underwater dance.

Amazing But True…

Did you know that many fishes can change gender during the course of their lives? Some fishes actually have both male and female sex organs.
Talk about equality! Did you know that with seahorses, the male is the pregnant partner? The female seahorse deposits her eggs into the pouch of the male. A seahorse “pregnancy” lasts about two to three weeks.
No batteries needed! Over half of deep-sea fishes actually produce their own light in the extreme darkness of the deep-sea environment. The secret to the fish’s bright idea is billions of tiny light producing bacteria (another example of a symbiotic relationship). If danger threatens, one such fish, the Flashlight Fish, can actually turn off its light by covering it with a curtain of skin.

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Related Science: Geography

Corals (and the symbiotic algae or zooxanthellae, that live in the coral) can only grow in a few regions of the world where there is adequate sunlight, shallow water, not too much silt, and where the water temperature is warm enough---but not too warm. Corals live in areas where the temperature ranges between 25° and 30° Celsius (77° to 84° Fahrenheit.) Because they are so sensitive to these conditions, corals are at risk of being damaged or destroyed when conditions change. Natural threats such as hurricanes and human activities including over-fishing, destructive fishing practices, coastal development and global warming, can destroy coral reefs.

According to the World Resources Institute (http://www.wri.org/biodiv/b02-koa.html), coral reefs occupy approximately 600, 000 square kilometers of the ocean, representing less than 0.2 percent of the total ocean area. They are located between 20 degrees North and 20 degrees South of the Equator. According to Reef Relief, there are three primary regions of the world where coral reefs are found. These regions are:

The Indo-Pacific region, which includes Indonesia, Southeast Asia, Australia and Polynesia.
The Western Atlantic area from Florida down to Brazil including the Caribbean area and the Gulf of Mexico.
The Red Sea. This area located between the East Coast of Africa and the Arabian Peninsula, is considered a separate area because of the high diversity of coral reef species found only in this region.

Reef Relief has a set of detailed maps showing the locations of reefs around the world. It can be found at http://reefrelief.org/learn/reef-hot-spots

Fringing reefs, the most common type of reef, form along a coastline. They grow on the continental shelf in shallow water.
Barrier reefs grow parallel to shorelines but are farther from shore and are usually separated from the land by a deep lagoon. They are so called because they form a barrier between the lagoon and the seas, protecting the coastline.
Coral Atolls are rings of coral reef growing on top of old sunken volcanoes in the ocean. They begin as fringing reefs surrounding a volcanic island; then, as the volcano sinks, the reef continues to grow, and eventually only the reef remains. There are over 300 atolls in the South Pacific. Atolls contain islands.

As the name implies, the Great Barrier Reef, located off Australia’s East Coast is the largest coral reef in the world. This enormous reef is over 2023 kilometers (1257 miles) long and covers more that 300,000 square kilometers (about 186,000 miles). Home to more than 1500 species of fish, dolphins, whales and sea turtles, the Great Barrier Reef is actually a collection of more than 3000 smaller reefs. The second largest reef lies off the coast of Belize in Central America.
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Deep Water Diving


Strap on your mask and fins and dive in to the world of deep-water science. While SCUBA (self-contained underwater breathing apparatus) diving can open up a new world full of fascinating underwater creatures, it can also be very dangerous. Here are a few of the most common problems divers face:

Have you ever swum to the bottom of a swimming pool and noticed that your ears begin to hurt? That uncomfortable feeling is caused by the weight of the water and air above you. As you get deeper, the amount of water over your head increases and so does the pressure. Although divers sometimes experience pain from the increased pressure underwater, the real problems occur when a diver surfaces improperly. Divers breathe compressed air through a regulator, which ensures that the air breathed into their bodies is at the same pressure as the surrounding water. But if they breathe compressed air underwater and then ascend, holding their breath, the pressure around them decreases, so that their lungs expand. Air sacs in the lungs can then rupture, causing an air embolism, in which bubbles of air enter the blood stream and may block circulation to the brain.

Despite how it sounds, “the bends” is not a new dance craze or a wild ride at your local amusement park. It is a potentially life threatening condition resulting from underwater pressure changes. Because 80% of the air we breathe (both directly and through scuba tanks) is nitrogen, our blood is always full of dissolved nitrogen. However, as a diver breathes via a tank underwater, the blood in his or her body can hold more nitrogen due to the increased water pressure. If the diver then returns to the surface of the water too quickly, the blood can no longer hold as much nitrogen at this lower pressure. As a result, nitrogen is forced out of the blood as tiny bubbles in the tissues, potentially causing severe joint pain (hence the name “the bends”), as well as dizziness, paralysis and even death. Divers can easily avoid these problems by limiting the depth of their dives and their time underwater and by following a few simple diving safety guidelines, such as following a pre determined dive plan and making a slow controlled ascent.

Although marine mammals, such as whales, dolphins and seals breathe air just like us, they don’t get the bends. When marine mammals dive, they hold their breath for staggering amounts of time. Sperm whales have been known to hold their breath for almost two hours when diving for food. Because they take air at the surface of the ocean, marine mammals do not get extra nitrogen in their blood and therefore have no danger of the bends. This also explains why people can free-dive (dive without tanks) without worrying about getting the bends. Although the average person has a difficult time holding their breath for more than a minute or two, some highly trained free divers can hold their breath for up to five minutes as they dive to depths well over 100 feet (30 meters).

Did you know that the record for the deepest underwater filming by a diver was recently set at 350 feet (106.68 meters) by renowned diver, Howard Hall, during the making of Coral Reef Adventure?
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Are you ready to make the plunge into the deep blue? Every diver needs to make sure they have the right gear, so let’s take a look at diving equipment.
The mask and snorkel

Unlike fish and marine mammals, humans require some help to see clearly underwater. This is where the scuba mask comes in. Because each of us is unique, masks vary in size, shape, lens color and even eyeglass prescription. The snorkel, although never used underwater (or you would end up with a mouthful of water), is important for surface swims back to the dive boat. The snorkel allows divers to breathe easily at the surface in spite of waves.

Fins and Wetsuit
Short of a nice layer of blubber and a powerful tail fluke, fins and a wetsuit are the only things that keep a diver warm and swimming properly. Because a dive in the tropical waters of the Caribbean is so different from a dive under the ice in Antarctica, wetsuits and fins come in a wide range of styles and thicknesses to accommodate changes in water temperature and ocean currents. A good wetsuit is essential for any diver, as the body loses heat much more quickly in water than in air. Likewise, a good pair of fins enables a diver to swim using far less energy and effort.

The Buoyancy Compensator (or BC)
Do you ever wonder how fishes hover effortlessly in the ocean while we must work tirelessly to stop ourselves from sinking to the bottom? The fish’s secret is a small air bladder that they can inflate or deflate to adjust their buoyancy. Divers have a special rugged vest called a buoyancy compensator that has a built-in air bladder to make it possible to adjust buoyancy. The Buoyancy Compensator, or “BC” in scuba lingo, also holds the diver’s air tank in place and hooks directly to the tank with a special hose. As divers descend they are compressed, effectively making them heavier for their volume than at the surface. BCs are used to overcome this effect so divers are able to stay at neutral buoyancy.

The tank

The average recreational diver breathes compressed air. The air is contained in a tank that divers carry on their backs. The typical tank is made of aluminum, weighs about 14 kg (31 pounds) empty and holds 2,265 L (80 cubic feet) of air at 1360 kg (3000 pounds) per square-inch (psi) (about the same amount of air as would fit in a telephone booth).

The regulator

Don’t try to breathe compressed air directly from a scuba tank or your lungs might take a beating due to the intense air pressure! Fortunately divers have developed a special mouthpiece and valve, called a regulator, that reduces the pressure from the tank to a pressure equal to surrounding water. The regulator also contains a special valve that efficiently provides air only when the diver inhales. The regulator actually consists of two separate pieces. The first stage attaches to the tank and reduces the pressure to a safe breathing level. The second stage supplies the air through a small mouthpiece

The gauges
Ever wonder how divers always seem to know how much air they have left and at what depth and in which direction they are swimming? The secret is the numerous gauges that divers carry as part of their standard equipment. Typically, divers carry a gauge that tells them the air pressure in the tank, a gauge that tells them their depth and a compass for navigation. These gauges are often arranged on a single console that clips to the diver’s BC. Nowadays, many divers carry a handheld dive computer that automatically calculates the amount of time a diver can safely stay underwater depending on the depth. Before computers, divers had “dive tables” to calculate bottom time for various depths.

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