Planaria in Aquariums

Planaria are flatworms that thrive on excess food and detritus. They can prey on shrimp eggs and weak fry and are removed by cutting feeding and targeted treatment.

Identification

Planaria are free-living flatworms of the order Tricladida that occur in marine, freshwater and terrestrial environments. In aquariums they appear as small whitish or tan worms with a distinctive blunt, triangular head, gliding over glass, substrate and decor using cilia and muscular contractions. They are sometimes confused with detritus worms but have the characteristic arrow-shaped head.

Causes

Planaria feed as predators and scavengers on small organisms and detritus, so their populations grow where there is abundant food. In aquariums this typically means overfeeding and accumulated organic waste, especially in shrimp and fry tanks where extra food is added. Reducing the food supply removes the conditions that let them multiply.

Risk to livestock

Planaria can prey on shrimp eggs and may attack weakened or newly hatched fry, making them a concern in shrimp-breeding tanks. They are also notorious for regeneration: very small pieces, estimated as little as a fraction of the body, can regrow into complete worms over a few weeks, so cutting or crushing them in the tank is counterproductive.

How to remove them

Reduce feeding sharply so the worms lose their food source.
Gravel-vacuum the substrate and perform water changes to remove detritus.
Trap them by removing them with a baited container or siphon rather than cutting them.
For shrimp-safe eradication, a fenbendazole-based treatment is commonly used; research dosing and tank safety before applying.

Prevention

Feed sparingly and remove uneaten food promptly.
Keep the substrate clean with regular vacuuming.
Quarantine and rinse new plants and decor.
Maintain good overall tank hygiene.