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Eels

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Flash
153463.  Sun Mar 04, 2007 10:45 am Reply with quote

Some of what follows is culled from the Eels thread in the E Series Talk forum. Some good stuff, posted by various people.

 
Flash
153464.  Sun Mar 04, 2007 10:46 am Reply with quote

Breeding / Migration

After spawning in the Sargasso Sea, European eel larvae swim across the Atlantic and enter rivers as elvers. They don't aim at a particular river, they just hit the European coasts in a broad band and swim up whatever river they encounter - so rivers with broad west-facing estuaries such as the Severn get lots of them. This was only worked out in 1922, partly because the larvae don't look anything like elvers and were not understood to be the same species until 1893. Indeed, until 1777 eels weren't even regarded as fish - they were thought to be worms (on the authority of Aristotle, as usual).

Quote:
"They migrate up rivers, overcoming all sorts of natural challenges sometimes by piling up their bodies by the tens of thousands to climb over obstacles and they reach even the smallest of creeks. They can wind themselves over wet grass and dig through wet sand underground for 30 miles to reach upstream headwaters and ponds, colonising the continent. ... In July their instinct drives them back towards the seas, crossing even wet grasslands at night to reach the proper rivers. Whether the adults can ever make the 4,000 mile open ocean journey back to their spawning grounds north of the Antilles, Haiti, and Puerto Rico remains unknown. By the time they leave the continent their gut dissolves, so they have to rely on stored energy alone."

 
Flash
153465.  Sun Mar 04, 2007 10:46 am Reply with quote

Proverbial eels

Erasmus uses the expression "holding the eel of science by the tail" to refer to the feeling you get when you try to explain something you don't understand properly yourself (at least I think that's what it means: 'cauda tenens anguillam, in eos apte dicetur, quibus res est cum hominibus lubrica fide, perfidisque, aut qui rem fugitivam atque incertam aliquam habent, quam tueri diu non possint' - not sure I understand it properly myself).

 
Flash
153466.  Sun Mar 04, 2007 10:47 am Reply with quote

Gulper eels (Saccopharynx lavenbergi)

look like cartoons.

 
Flash
153470.  Sun Mar 04, 2007 10:53 am Reply with quote

Electric eels, I might add

I think electric eels are a subject in themselves, not least because they aren't really eels, but knifefish: the wiki says that "The species is so unusual that it has been reclassified several times. Originally a species in Gymnotus, it was later given its own family Electrophoridae, and then demoted to a genus of Gymnotidae alongside Gymnotus."

The Prussian explorer Humboldt (qv in the Exploration thread when I get round to him) has a great account of South American Indians fishing for electric eels with horses; they drove the horses into the water so that the gymnoti expended their electricity on them. I'm pretty sure there has to be a question in this, either under electricity, eels, or explorers.

Quote:
To catch the gymnoti with nets is very difficult, on account of the extreme agility of the fish, which bury themselves in the mud. We would not employ the barbasco, that is to say, the roots of the Piscidea erithyrna, the Jacquinia armillaris, and some species of phyllanthus, which thrown into the pool, intoxicate or benumb the eels. These methods have the effect of enfeebling the gymnoti. The Indians therefore told us that they would "fish with horses," (embarbascar con caballos.* (* Meaning to excite the fish by horses.)) We found it difficult to form an idea of this extraordinary manner of fishing; but we soon saw our guides return from the savannah, which they had been scouring for wild horses and mules. They brought about thirty with them, which they forced to enter the pool.

The extraordinary noise caused by the horses' hoofs, makes the fish issue from the mud, and excites them to the attack. These yellowish and livid eels, resembling large aquatic serpents, swim on the surface of the water, and crowd under the bellies of the horses and mules. A contest between animals of so different an organization presents a very striking spectacle. The Indians, provided with harpoons and long slender reeds, surround the pool closely; and some climb up the trees, the branches of which extend horizontally over the surface of the water. By their wild cries, and the length of their reeds, they prevent the horses from running away and reaching the bank of the pool. The eels, stunned by the noise, defend themselves by the repeated discharge of their electric batteries. For a long interval they seem likely to prove victorious. Several horses sink beneath the violence of the invisible strokes which they receive from all sides, in organs the most essential to life; and stunned by the force and frequency of the shocks, they disappear under the water. Others, panting, with mane erect, and haggard eyes expressing anguish and dismay, raise themselves, and endeavour to flee from the storm by which they are overtaken. They are driven back by the Indians into the middle of the water; but a small number succeed in eluding the active vigilance of the fishermen. These regain the shore, stumbling at every step, and stretch themselves on the sand, exhausted with fatigue, and with limbs benumbed by the electric shocks of the gymnoti.

In less than five minutes two of our horses were drowned. The eel being five feet long, and pressing itself against the belly of the horses, makes a discharge along the whole extent of its electric organ. It attacks at once the heart, the intestines, and the caeliac fold of the abdominal nerves. It is natural that the effect felt by the horses should be more powerful than that produced upon man by the touch of the same fish at only one of his extremities. The horses are probably not killed, but only stunned. They are drowned from the impossibility of rising amid the prolonged struggle between the other horses and the eels.

We had little doubt that the fishing would terminate by killing successively all the animals engaged; but by degrees the impetuosity of this unequal combat diminished, and the wearied gymnoti dispersed. They require a long rest, and abundant nourishment, to repair the galvanic force which they have lost.* (* The Indians assured us that when the horses are made to run two days successively into the same pool, none are killed the second day. See, on the fishing for gymnoti Views of Nature Bohn's edition page 18.) The mules and horses appear less frightened; their manes are no longer bristled, and their eyes express less dread. The gymnoti approach timidly the edge of the marsh, where they are taken by means of small harpoons fastened to long cords. When the cords are very dry the Indians feel no shock in raising the fish into the air. In a few minutes we had five large eels, most of which were but slightly wounded. Some others were taken, by the same means, towards evening.

A. von Humboldt, A. Bonpland - Travels to the Equinoctial Regions of America, 2
http://explorion.net/a.von-humboldt-equinoctial-regions-america-2/page-62.html

(Chapter 24 of the same book explains inter alia how they made curare, the poison used on poison-tipped arrows: http://www.globusz.com/ebooks/Equinoctial2/00000020.htm)

 
Flash
153471.  Sun Mar 04, 2007 10:55 am Reply with quote

Hagfish

Apparently there's an urban myth to the effect that a wallet made out of electric eelskin will de-magnetise your credit cards. Evidently this is untrue, not least because electric eelskin wallets are made from hagfish, not electric eels.

As noted above, eels were not understood to be fish until 1777; conversely, hagfish may not be fish, since they are much more primitive than any other fish group and perhaps invertebrate. They eat their prey from the inside out, by crawling into living or dead fish and then eating their surroundings, and can literally tie themselves into knots: "When hagfish wish to disengage from their current prey, they form a knot with their body and slide it towards the mouth. The knot provides something to press against in order to pull the mouth off. This is a unique trait." Note for picture researchers: Blue Planet apparently had film of this - any point in trying to get hold of it, Helen?

 
Frederick The Monk
153476.  Sun Mar 04, 2007 11:19 am Reply with quote

Hagfish can extrude astonishing quantities of fibre re-enforced slime which expands dramatically on contact with water. It is thought that this is a defence mechanism to help it slip away from predators. One drawback of this is that there is a danger that the hagfish will suffocate in its own slime. To prevent this it does the old 'tie itself in knots' trick again, sliding the knot down its body, wiping off the slime.

More details at Hagfish Slime Research.

 
Frederick The Monk
153477.  Sun Mar 04, 2007 11:21 am Reply with quote

Which reminds me, I have seen footage of a hagfish in a bucket of seawater being 'stirred'. Within a few seconds the whole bucketful of water turned to thick clear slime, a bit like wallpaper paste.

Yum.

 
Frederick The Monk
153481.  Sun Mar 04, 2007 11:25 am Reply with quote

The Long-Finned Eel is a big'un.

Monster eels 10 feet long caught in New Zealand

 
Flash
153482.  Sun Mar 04, 2007 11:27 am Reply with quote

Back to basics on the electric eels:

They live in the Amazon and Orinoco areas of S America, can be 8 feet long and weigh 20 kg. They live on the bottom of the body of water they inhabit but have to surface.every ten minutes to breathe. They communicate with each other by emitting 10V electric signals but when using electrical pulses to stun prey or deter attackers they can emit 500V (and 1 amp).

The electricity-producing organs take up the whole of the hindmost 80% of the eel's body. They consist of thousands of stacked plates which produce electricity in a similar way to batteries.

There are also electric catfish and electric rays.

 
Frederick The Monk
153484.  Sun Mar 04, 2007 11:27 am Reply with quote

The biggest Conger Eel ever recorded was a gigantic fish of 350lb found trapped in nets off Iceland's Westmann Islands.

The british Conger Club has details.

 
Flash
153488.  Sun Mar 04, 2007 11:40 am Reply with quote

The electric catfish is 3ft long, lives in Africa, and operates at 350V. The electric ray is a marine fish found in the Gulf of Mexico and operates at 220V. There are 69 species, but the best known are in the Genus Torpedo - superficial etymology buffs will be interested to know that this is where the name of the weapon comes from but only real enthusiasts will wish to know that this name in turn comes from the Latin torpere, to be numb (as does torpor).


Last edited by Flash on Sun Mar 04, 2007 11:46 am; edited 1 time in total

 
Frederick The Monk
153491.  Sun Mar 04, 2007 11:43 am Reply with quote

The reason torpedo fish got their name from the Latin verb 'to numb' is because the ancient Greeks used their electrical discharges as an anaesthetic.

 
Frederick The Monk
153492.  Sun Mar 04, 2007 11:46 am Reply with quote

The first written document on the medical application of electricity is from the year A.D. 46, when Scribonius Largus recommended the use of torpedo fish for curing headaches and gouty arthritis (Kellaway, 1946)

 
Flash
153493.  Sun Mar 04, 2007 11:47 am Reply with quote

That's good. So not just the Gulf of Mexico, then - are they found in the Med?

 

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