March 22 is World Water Day. Water is essential for all of us and we cannot live without drinking water. In fact it is believed the life of the Earth began in water, so Earth is indeed a water planet. ZooLander looks at the amazing diversity in aquatic animals.
We
can live for a few days without food, but can we even think of
surviving without water. But there are some animals that need water
based mediums to live in, as if their very survival is dependent on
water. These are aquatic animals and live in water for most or all of
their life. We breathe through our lungs, but most of these aquatic
animals, like fish, use their gills, a special organ that can extract
the oxygen from water. However there are other aquatic animals such as
whales and dolphins that breathe air directly from the atmosphere. The environments these aquatic animals live in are of two types - freshwater or saltwater. Creatures that live in saltwater mediums like the oceans are known as marine species. Zoos and aquariums are the best places for observing these animals and the best place in Sri Lanka to study marine species in captivity, is at the aquarium in the Dehiwala zoo. Diving or snorkeling is the other option, if you want to see them in their natural habitat. As many of us cannot swim or dive in to the vast oceans and as it is also a specialized technique that needs to be learnt and practiced, the majority has to go to aquariums to study these beautiful animals.
The zoo aquarium is full of freshwater fish. There are lots of endemic fish species that are native to Sri Lanka, which cannot be found anywhere else in the world. This section in the aquarium is the most important and interesting corner to watch. There are other interesting river fish from other parts of the world too that you can observe at the aquarium. Zoolander has previously reported on the aquarium’s freshwater inhabitants - the giant Amazonian fish Arapima, notorious Piranha and the endemic Sri Lankan fish Pathirana Salaya. There are other interesting fresh water fish swimming in lit-up tanks, placed in darkened passages.
The aquarium is also home to many varieties of marine fish. Those who are associated with corals are the most beautiful of them. Can you recall the Moray eel that Zoolander reported on sometime back? It’s an interesting creature found in coral habitats. On a visit to the Dehiwala zoo, one can observe many such aquatic creatures in the aquarium.
Whales and Dolphins are the most popular aquatic mammals, but none of them can be seen in captivity in Sri Lanka. However, the Dehiwala zoo is not without a representative of the aquatic mammal family. The performing sea lion is the only aquatic mammal at the Dehiwala zoo and with the daily performances, it is one of the most popular characters, entertaining visitors.
Amphibians are another aquatic form of animals that can live both on water and land and the aquarium still has its corner for frogs.
Fish gills
Have you gone to the fish market to buy fish? Or have you seen the fish on the kitchen table ready for cooking? If not, have a look at the head of a small or medium sized fish and you will notice the gills, which are used for breathing by taking oxygen from water. But how do these gills function? Have you ever given a thought to it?
The gills allow fish to absorb oxygen from the water and in the fish they do the work, of lungs. In lungs, blood in tubes flow near the surface of tiny air sacks, oxygen transfuses from the air in the sacks into the blood, and carbon dioxide transfuses from the blood to the air in the sacks. A fish’s gills work exactly the same way, except that it is water in the gill structures that handle the transfusion, and are visible dangling in the open water instead of being hidden inside the lungs.
Gills themselves have a car radiator-like appearance. Most fish have 4 gills on each side, consisting of a main bar-like structure that has numerous branches as those found on a tree, and the branches consisting of even smaller branch-like structures. This arrangement of cells allows for a very large surface area when the gills are immersed in water.
Functionally, the mechanism for pumping water over the radiator-like gills seems to vary depending on the species of fish. In general, a fish is able to reduce the pressure in its mouth cavity by lowering the floor of the mouth and widening the outer skin flap that protects the gills, called the operculum. This increase in volume lowers the pressure within the mouth causing the water to rush in. As the fish raises the floor of their mouth, an inward fold of skin forms a valve of sorts which doesn’t allow water to rush out. The pressure is then increased compared to the outside of the mouth and the water is forced through the operculum opening and across the gills.
This wonderful organ, the gill, has allowed fish for millions of years to enjoy the wonder that is underwater basket weaving. The next time you see a fish swimming around you can smile to yourself knowing that they are working much harder than us to breathe.
Fish that can live outside water
If you happen to watch the popular Sinhala TV programme Atapattama, you may have seen a large Gourami fish that comes out of the water and even allows children to cuddle it for about 15 minutes outside water. It became fascinating news and got much publicity. But fish experts say this is not a new phenomena and fish like the Gourami have the ability to live outside water for a longer time as they have another special organ in addition to gills that allows them to absorb atmospheric oxygen. This organ is called a labyrinth organ which acts as a lung helping the fish to breathe in air, allowing labyrinth fish to take in oxygen directly from air, instead of taking it from the water in which they reside with the use of gills. The labyrinth organ helps the inhaled oxygen to be absorbed into the bloodstream. As a result, labyrinth fish can survive for short period of time out of water, as they can inhale the air around them, provided they stay moist.
Labyrinth fish are not born with functional labyrinth organs. The development of the organ is gradual and most labyrinth fish breathe entirely with their gills and develop the labyrinth organs when they grow older as per the experts who studied this fish variety. It is not unique to Gouramis -- if you remember ZooLander wrote about this special organ, when reporting about the zoo aquarium’s Dino Fish - Arapaima. The Arapaima lives in the Amazon and they too have the labyrinth organ.
Aquatic creatures are very interesting animals, even though we are not as familiar with them as with land animals. The zoo’s aquarium will provide a good opportunity for you to observe these fish. How they breathe underwater, how they swim, how they interact. Why not make a visit to the zoo once again and carefully observe these aquatic marvels and be delighted by them
Interesting facts about fish and other aquatic creatures
1. Sea turtles absorb a lot of salt from the sea water in which they live. They excrete the excess salt from their eyes, which makes them look as though they’re crying.
2. Prehistoric turtles may have weighed as much as 5,000 pounds.
3. As it gets older the cockle just adds another layer to its outer shell. To work out their age you can count the rings on them just like on a tree.
4. A goldfish has a memory span of three seconds.
5. A male angler fish attaches itself to a female and never lets it go. Their vascular systems unite and the male becomes entirely dependent on the female’s blood for nutrition.
6. Beavers can hold their breath for 45 minutes under water.
7. The sailfish is the fastest swimmer, reaching 109 km/h (68 mph).
8. The slowest fish is the sea horse, which moves along at about 0.016 km/h (0.01 mph).
9. The heart of a blue whale is about the size of a small car.
10. The tongue of a blue whale is as long as an elephant.
11. The largest jellyfish ever caught measured 2.3 m (7’6”) across the
belly with a tentacle of 36 m (120 ft) long.
12. Fish and insects do not have eyelids - their eyes are protected
by a hardened lens.
www.whereincity.com
About World Water Day
International World Water Day is held annually on March 22 to focus attention on the importance of fresh water and advocating for the sustainable management of fresh water resources.
An international day to celebrate fresh water was recommended at the 1992 United Nations Conference on Environment and Development (UNCED). The United Nations General Assembly responded by designating 22 March 1993 as the first World Water Day.
Each year, World Water Day highlights a specific aspect of fresh water. This year’s theme is “water and food security”.
Published on LakbimaNews on 25.03.2012
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