View previous topic | View next topic

Eels

Page 1 of 3
Goto page 1, 2, 3  Next

gerontius grumpus
81241.  Sun Jul 23, 2006 8:12 am Reply with quote

Eels are quite interesting, they are some of the few catadromous fish, they spawn in the sea and migrate to fresh water where they grow to maturity.
both the European eel Anguilla anguilla and the American eel Anguilla rostrata spawn in the Sargasso Sea.
The European eel larvae then have to swim across the Atlantic before entering rivers as elvers.
Elvers are caught in the river Severn near Gloucester where they are considered a delicacy.

 
Flash
81246.  Sun Jul 23, 2006 9:05 am Reply with quote

GG - so they 'know' to migrate to somewhere they've never been before? Has this behaviour been studied much, do we know? EG, what would happen if you moved some eggs to somewhere other than the Sargasso Sea - would the elvers still end up on the plates of the Gloucestershire epicures, or would they go someplace else, or what?

 
gerontius grumpus
81251.  Sun Jul 23, 2006 9:30 am Reply with quote

Wiki. has quite a lot about eel and eel larva migration.
Yes it has been studied a lot. The larvae are highly efficient swimmers. They come across the Atlantic, aided by NAD etc. and hit the European coasts in a broad belt and swim up whichever rivers they encounter.
The point about the Severn estuary is that it's funnel shaped and elvers from a wide area of sea end up in just a few rivers.

 
swot
81268.  Sun Jul 23, 2006 11:10 am Reply with quote

I think I read somewhere that electric eels aren't 'true' eels because they don't have a dorsal fin, or something like that. They're just eel-like so they're called eels in the same way that koalas are called Koala bears.

 
Flash
81270.  Sun Jul 23, 2006 11:12 am Reply with quote

So all they really need is two instincts (to swim with the current and to seek fresh water), and they'll likely end up in a European river?

I know what you're thinking: that I should go and do my own research. And you're right. Back soon.

 
Flash
81271.  Sun Jul 23, 2006 11:15 am Reply with quote

No1, you're right - it's a knifefish, not an eel. Not sure what that means, but the wiki says:
Quote:
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.

Even less sure what that means.

 
swot
81274.  Sun Jul 23, 2006 11:18 am Reply with quote

Hooray! Lion King Magazine strikes again. Possibly.

 
Flash
81275.  Sun Jul 23, 2006 11:21 am Reply with quote

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.

 
swot
81277.  Sun Jul 23, 2006 11:23 am Reply with quote

Where is the electricity generated in the electric 'eel'? Surely it wouldn't stay in the skin after it had been made into a wallet. Some people will believe anything.

 
Flash
81279.  Sun Jul 23, 2006 11:36 am Reply with quote

Eels were not believed to be fish until 1777, when Carlo Mondini proved that they were. Until then Aristotle's assertion that they were worms was widely accepted.

One of the problems was that elvers don't look anything like adult eels, so no-one could figure out what the lifecycle was (larval eels were considered to be a separate species until 1893).

The business about the Sargasso Sea wasn't worked out until 1922, when Johnannes Schmidt followed the trail of smaller and smaller larvae to the Sargasso (an area of the Atlantic south of Bermuda). It takes the little blighters three years to get to Britain, then:
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
81281.  Sun Jul 23, 2006 11:46 am Reply with quote

Conversely, hagfish may not be fish, since they are much more primitive than any other fish group. Even so, they can literally tie themselves into knots, which is more than I can do these days (I'm not as young as I was). They eat their prey from the inside out, by crawling into living or dead fish and then eating their surroundings.

It isn't even clear whether they are vertebrates or not.

Quote:
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.

I should jolly well hope so.

http://en.wikipedia.org/wiki/Hagfish

 
dotcom
81282.  Sun Jul 23, 2006 11:50 am Reply with quote

Flash (:
The eelskin wallet thing is an urban myth - it was tested on the TV programme "Mythbusters" a while ago.
You can see the wiki page here
http://en.wikipedia.org/wiki/MythBusters_(season_1)#Eelskin_Wallet


Last edited by dotcom on Sun Jul 23, 2006 11:55 am; edited 1 time in total

 
Flash
81284.  Sun Jul 23, 2006 11:52 am Reply with quote

Thanks, dot. Apparently there is some possibility that a magnetic clasp on the wallet could have the effect complained of.

 
swot
81285.  Sun Jul 23, 2006 11:54 am Reply with quote

Mythbusters starts on BBC2 this Thursday at 7.30, so no-one has an excuse not to watch it.

 
dotcom
81289.  Sun Jul 23, 2006 12:08 pm Reply with quote

At long last!

I think they tested the cards under really strong magnetic conditions, though, and they still didn't wipe. That's what they usually do on Mythbusters, just to see. I've googled around a bit and there's mixed thoughts - some people say they do wipe because of the clasp, others have had no problems.

 

Page 1 of 3
Goto page 1, 2, 3  Next

All times are GMT - 5 Hours


Display posts from previous:   

Search Search Forums

Powered by phpBB © 2001, 2002 phpBB Group