fears over plans to use poison on Enfield brook

Its a difficult one this. A piscicide is really the only way to deal with the top mouth but I've not heard of it being used in running water before. I'd be interested to know just how they will prevent it spreading downstream of their chosen site and how they know that there are no TMG further downstream.

wot have the rspb got to do with it, should't angling trust be on this

They probably see TMG as bird killers  

Neil Depledge wrote:

Its a difficult one this. A piscicide is really the only way to deal with the top mouth but I've not heard of it being used in running water before. I'd be interested to know just how they will prevent it spreading downstream of their chosen site and how they know that there are no TMG further downstream.

thats kinda what intrigued me, just how do they limit the distance this stuff affects?
will it just dilute itself to the point of becoming harmless?
& why wont it just push the topmouths further down the brook?

Very difficult one - seems a terribly risky thing to do, with no guarantee that it will even eradicate all the topmouth gudgeon present.   Have to trust that they know what they are doing?  Hopefully they will thoroughly electro-fish and net the whole brook first to remove the native residents (though electro fishing is less effective on smaller fish).  On the other hand, the risks of leaving them in there could be that the native species disappear, no more angling.

EA fact sheet: http://www.environment-agency.gov.uk/static/documents/Leisure/Topmouth_gudgeon_fact_sheet.pdf
This is more informative: http://www.invasivespeciesscotland.org.uk/asian-topmouth-gudgeon-pseudorasbora-parva/
Rotenone: http://en.wikipedia.org/wiki/Rotenone - contrary to the un-cited wikipedia comment "In water, rotenone may last six months" this paper suggests that it has a half-life of 0.5 - 3.5 days in water (depending on temperature) and it is usual practice to neutralize it afterwards with potassium permanganate which rapidly oxidises it to a less harmful form.

This article provides a bit more detail on the process: Environment Agency poisons Hampshire lakes to kill invasive fish

certainly gonna be one to watch. i reckon theres going to be trouble either way this pans out. imagine the e.a have a stock of native fish, they poison this stretch, somehow managing not to let it escape downstream, then amazingly all the tmgs wind up dead, then a brilliant clearup sweep of the section happens, all the bodies of all the fish killed are collected. the native ones are identified counted and weighed. then when the conditions are right the e.a. re-introduce the natives and they live happily ever after. what do ya reckon would happen next? i think they will go spreading the stuff just about anywhere they can find an invasive species, and the outcome may not be quite as happy as the one ive just outlined. on the other hand, the poison could go in and there could be some kind of foul-up which i believe is quite common if real people have to measure stuff carefully, and well someone else can finish that story.