NANFA-- Rivulus, Roach and Pike

Pete Liptrot (
Fri, 5 Dec 2003 00:11:11 -0000

> That sounded so wierd when I read it. I should have guessed it might not
> correct. Is the roach native to Ireland?
I've tried to reply to this twice, and my PC locked each time.Must be a
taboo topic or something...
No, the Roach is not native to Ireland. It was introduced during the late
19th C, and in recent decades has spread particularly quickly as a result of
increased popularity of angling holidays there (nearly all based on
non-native Cyprinids).
Todd, the North Sea is on the East side of the UK, between us and Europe.
Ireland is off the West coast, closer to where I am. If I drive the 30 miles
or so West to the coast and look across to Ireland the body of water in the
way is called, somewhat appropriately, the Irish Sea. Geography lesson
All the West coast rivers of the UK mainland historically had a depauperate
fish fauna, because we were under a serious depth of ice only 10,000 years
ago. The East coast rivers had a far richer ichthyofauna, including many
Cyprinids, due to recolonizations from the mega-Rhine in the interval after
the glaciers retreated and before the North Sea was formed. We've been
moving stuff around for the past few thousand years, so the true
distributions of fish spp. are no longer obvious except through
archaeological investigations.
Because of this there weren't any Cyprinids on adjacent areas of the UK
mainland to make it back across to Ireland after the Pleistocene glaciation,
before the Irish Sea was formed (I think that the intervening gap was deep
enough for there always to be a stretch of marine water there in any case).
This is the reason why Ireland developed a very interesting fauna based
mostly around different forms of Salmo trutta, the Brown Trout. Without
competition, they could occupy niches other than those traditionally
occupied by this species, such as pelagic lacustrine planktivores. These are
well on their way to speciation, but there must be just enough gene flow to
avoid this (those that haven't been lost due to introduction of non-natives,
anyway). They appear to be the result of sequential colonizations of
different stocks of S. trutta, really odd in appearance.

> Come to think of it, are Pike native to Ireland?
No, but the introduction took place at a much earlier date if I remember
correctly. There is now certainly some very good Pike fishing in Ireland.
They don't quite get to the size of the Muskellunge, but they reach around
50lbs both in Ireland and here on the UK mainland.
Our Pike is Esox lucius, the same as your Northern Pike. There are fossils
of Pike that show them to be little changed in the past 50 Million years,
and their distribution is another clue to their long evolutionary history.
Another genus common to both Europe and North America with a long history is
Perca. We have P. fluviatilis, you have P. flavescens. Not that much
difference. Again 50 Million-year old fossils are known.
Then there are the Mudminnows, Burbot, Thymallus.....
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