Animal of the Week February 20, 2014 -- Holy carp!

When might a fish give you a black eye? When it's this week's animal of the week Hypophthalmichthys molitrix (silver carp), that's when.

This species made headlines this week when the US Government charged US Army Corps of Engineers to suggest ways in which they might prevent this invasive species from Asia reaching the Great Lakes, amid fears for the impact they and their close relative the bighead carp will have on these landmark ecosystems of the USA–Canada border.

Since their introduction to the southern Mississippi area of the USA three decades ago, they have made it all the way up the Mississippi, Missouri, and Illinois river systems. At points reaching phenomenal densities. Silver carp have a habit of leaping out of the water when spooked by loud noises such as boat engines, people have suffered broken noses, broken jaws, and broken vertebrae when hit by spooked fish. This video clip has no such outcomes but much good humour:

In Bath Illinois, the Redneck Fishing Tournament will  celebrate its 10th anniversary this year, in which people with nets catch the fish as they leap out of the water. The only rules: no fishing poles and do it at your own risk.

Silver carp are excellent filter-feeders, with specially designed gills that enable them to extract all but the tiniest particles from water. They can filter out particles 4 micrometres in diameter, have no need for stomachs because the particles they eat are so small, and they might never actually stop feeding. For this reason, they were introduced to the USA to help control algae in water treatment plants and catfish farms.

They can grow to a metre in length and reach 40 kg, and this ability to turn such tiny yet abundant food into so much body mass makes them ideal for farming, and they are the most farmed fish in the world. If you find that unbelievable because you've never seen a silver carp farm, but have fond childhood memories of trips to trout farms? That's because you've not grown up in China where most of the silver-carp farming happens.

Their habit of leaping out of the water

Previous introduced species AOTWs include the  snakehead and the harlequin ladybird.