Where: Florida, USA
October 16, 2000: The recent emergence of a large number of unfamiliar eels in the waters off the coast of Florida in South-east America, is causing worry to local ecologists there. They fear that the new arrivals, eels of Asian origin, will disturb the food chain of the region with their voracious appetites.
What exactly are eels ? They are slippery serpent-like fish, inhabiting shallow coastal waters throughout the world. They are fairly common in the freshwaters of eastern and south-eastern America.
The species native to this region are known as American eels and spend their adult lives in freshwater and return to the southwestern Atlantic, to spawn. The young eels (known as elvers) return to freshwaters and the cycle continues.
Florida’s warm, wet climate provides ideal conditions for breeding and several non-native fish from Africa and Asia spawn in its waters. Until now they have not caused a drastic impact in the food chain as they never reached large numbers. Besides they never managed to reach the deep interior of Florida’s Everglades National Park. (Most fish get stuck in marshland and die before reaching the interior.)
Strangers in the Water
But Asian eels enjoy an edge over American eels. Over 3 foot long, they are a lot stronger and hardier than their American cousins. Being highly adaptable Asian eels have both gills and lung-like organs to breathe; as a result they can survive in swamps, drains and water canals, as well as in ponds and rivers. Sometimes, when water bodies dry up, these eels slither into mud or grass and are able to live there for as long as several months without food !
Strangely enough, no one is sure how the Asian eel first arrived in Florida, but some biologists suggest, the eels may have been released, by someone who had tried to raise the species on a fish farm. Although these eels have not reached the interior of the Park, their numbers are rapidly increasing and it is estimated that there are thousands of eels in the vicinity and in the outlying canal systems.
The problem is finding a way to stop it. (Studies reveal the eels are not affected by fish poisons, nor can they be netted, as they are quick to take shelter in crevices).
The Asian eel is not fussy about food, it consumes almost everything that it finds edible – from frogs to small fish, to shrimp and turtle eggs!
The Vacuum-cleaner Mouth
The eel uses its mouth as a vacuum cleaner and sucks in smaller creatures. Now that’s worrisome to ecologists, who fear the Asian eels could consume food supplies of native fish and wading birds in Everglades National Park. Ecologists point out that the alien species might gradually replace other native predators in the food chain. Some fear that this variety could spread even further and might penetrate large portions of the United States if left unchecked.
More on the Eel
Eels are lithe swimmers. Most species are less than 3 ft long. One species, known as the conger eel, is found in the Atlantic Ocean and is known to grow up to 9 ft long. Eels can be divided into nearly 600 different species – and are found all over the world, in seas, freshwater and oceans. Most eels have no scales and are protected by a layer of slippery mucus. Some freshwater eels can absorb oxygen directly from air or water, through their skin.
The eels hatch from eggs. Initially they do not resemble eels at all, and are transparent and small. They drift about ocean surfaces for as long as three years, feeding on algae until they grow into frisky young eels called elvers. That is when their appetite undergoes a drastic change and they begin eating fish, crabs, and other invertebrates.
These Eels can Shock!
Did you know that a certain species of eel emit strong electric shocks? The electric eel, native to the Orinoco River and the rivers of South America, can deliver whopping voltages. They do so in order to stun their prey while hunting or in self-defense.
An electric eel’s sting can carry five times the voltage of a household socket while larger electric eels (5ft to 7ft) long produce about 600 volts – enough to stun a horse. However if the eel discharges a lot in a short interval, it gets exhausted and needs sufficient rest to ‘recharge its batteries.’
Electric fishes (like the electric eel, electric catfish, and the electric rays) or those eel who can emit electric shocks, are capable of generating a strong electric field. This happens because their body contains a special organ called the electric organ. In the case of the eel, these cells are concentrated in the tail, which occupies about four-fifths of the total length of the fish.
The electric organ consists of stacked, platelike cells called electroplates that are organised into many small blocks of muscle on either end of the electric organ.
The electroplates behave exactly like the two ends of a battery. If you have ever noticed, the two ends of the battery are marked positive (+) and negative (-). These are known as the cathode and anode respectively.
The chemical within the battery causes an electric flow from the anode to the cathode (ie. negatively charged sub-atomic particles from the anode, called electrons, get attracted to the positively charged cathode, and this is what results in a flow of current).
The two ends of the electric organ thus generate a strong electric field and nerves branching throughout the electric organs distribute the charge, which intensifies as it passes through the electroplates, delivering a ‘neuro-electic’ (electric pulses transmitted by nerves) shock.