Last Friday, after Robsac School's pond dipping session, we found a small pond animal swimming around in the container which was pointed out by one of the children. We had already chosen the 10 pond creatures for the broadcast so it was not mentioned.
However this fascinating pond creature is called Argulus also known as a fish louse. Argulus is a parasite and looks like a creature from a science fiction movie. It would be easy it believe this monster came from another world; in fact this is partly true as the Argulus comes from the murky world beneath the surface of ponds and rivers.
Lucky for us, this is a mini monster as it only reaches 8 mm in length.
The children caught three stickleback fish during their pond dipping session and the fish louse was probably originally attached to one of the sticklebacks. After the children caught the sticklebacks - the fish louse probably let go of the fish.
This parasite lives on the body of fish where it feeds on their blood. The fish louse has two suckers on the underside of its head which allow it to walk along the side of the fish it is feeding on. In between the two suckers is its needle-like mouth which it uses to pierce the fish’s skin and feed on its blood. The 2 videos below are part of a library of shots we assembled a year ago with the Nature Corridors for All group who you can hear in the background.
An infested fish will often swim and flick its side again objects to try to dislodge the parasite. If the fish becomes too infested by a number of fish lice then the fish may be weakened and die. The fish louse has a perfectly adapted streamlined shape so that when it is attached to a fish the water will flow over its body and not wash the fish louse off.
The fish louse has 8 short legs and can swim to find another victim.
This is an external parasite, which means it lives on the outside of the hosts body.