Beneath the surface of the UK's rivers and canals these Glass Eels are the centre of a murky underworld of illegal trade.
They develop into the highly sought after European Eel.
While the main trade is primarily in France and Spain, smugglers here in the UK will also offer way above the legitimate market value of - around £150 or $190 US Dollars a kilo.
(SOUNDBITE) (English) ANDREW KERR, CHAIRMAN, SUSTAINABLE EEL GROUP, SAYING: "And you can get up to 100 - thousand glass eels into a suitcase.
And if they're leaving Europe at a euro each then that's 100 thousand pounds in your suitcase and then at the other end, you grow them on in a pond in China and a year later that's a million.
A million euros worth!" Hundreds of millions of these eels migrate into Europe's waterways from the North Atlantic every year and while that sounds like a large number - the decline of the species has seen it land on the critically endangered list.
EU restrictions were imposed in 2010 and it's illegal to sell these eels outside of the EU.
(SOUNDBITE) (English) ANDREW KERR, CHAIRMAN, SUSTAINABLE EEL GROUP, SAYING; "Japan, China, South Korea, they are all great eel eaters.
But remember, they're also re-exporting them to North America and back to Europe again." This raid was carried out in the South of Spain last year.
Civil Guard officers arrested 10 people.
Top officials from around the EU gathered in London to discuss the joint action of authorities.
(SOUNDBITE) (English) IAN GUILDFORD, INVESTIGATIVE SUPPORT OFFICER, UK NATIONAL WILDLIFE CRIME UNIT, SAYING; "There is a lot of legal trade that takes place, so when you've got a legal trade and an illegal trade going side by side it's sometimes very difficult to try and combat that." Law enforcement admits it's a tough task.
But is eel trafficking really the world's biggest wildlife crime?
(SOUNDBITE) (English) IAN GUILDFORD, INVESTIGATIVE SUPPORT OFFICER, UK NATIONAL WILDLIFE CRIME UNIT, SAYING; "It is getting very close to being the top.
When you look at the monetary returns on the illegal market, then yes it is approaching one of the major wildlife crimes." The attention at the moment is firmly on catching the smugglers.
And their chances of slipping through the net, are getting smaller.