Planaria
Planaria are a free-living flatworm found in almost every kind of environment, on land and in fresh and salt water. They are a very small black or brown flatworm that look very similar to leeches and often appear in freshwater aquariums. They are generally around 3 to 5 mm long, but some grow as large as 10 mm. In a normal aquarium situation they usually don't cause any problems and probably even go unnoticed. However, if you get them in a breeding aquarium, they can destroy a whole spawning of eggs within hours. They are usually seen crawling around on the front of the aquarium after the lights have been turned off. They feed on anything organic but can also infect the mucous membranes of the fish's gills. They feed by sucking food into their gastrovascular cavity through a tube called the pharynx located on the mid-ventral surface.
Planaria belong to the Phylum Platyhelminthes, Class Turbellaria, and Order Tricladida. The genus Planaria, has apparently has been replaced by an older name, Dugesia. Planaria come in a number of species and strains, some of which are albino. The following species have been reported from freshwaters, Dugesia tigrina, Dugesia dorotocephala, and Dugesia tigra. Dugesia notogaea has been recorded from northern Queensland.
Planaria are also able to reproduce asexually both by binary fission, that is, by pinching themselves apart to become two and by regeneration, producing an entire new worm from a piece that has been cut off. If the head is split, both halves will grow back the other half. Movement may be accomplished either by muscular contractions of the body wall or the use of cilia along the ventral surface. When using the cilia the planarian appears to be gliding across the surface.
Spawning mops are commonly used by enthusiasts for breeding many rainbowfish species. However, before using them in different breeding tanks, it is advisable to always sterilise the mops to kill any planaria, or other pests that may be present. This can easily be accomplished by washing them in boiling water. Another method is to soak them in a chlorine solution, then thoroughly rinsing them before being sun-dried. This is where spawning mops offer a significant advantage over live plants as a spawning medium.
