Philodina roseola

Today we will talk about one of the most common microscopic invertebrate organisms that inhabit freshwater aquariums and play an important role in the functioning of aquatic ecosystems. In this article we will be looking at what Philodina roseola is, what it does in your aquarium and if it is dangerous to your fish.

What is Philodina roseola?

Philodina roseola is an invertebrate microorganism from the class Rotifera, which includes more than 2,000 species. These animals are found in freshwater bodies all over the world, including lakes, ponds, rivers, aquariums and even temporary pools.


Philodina roseola is only 0.2 mm long, making it difficult to see with the naked eye, but if we take a sample from the bottom of the aquarium, we will probably find it. Due to their small size, rotifers are an important food source for young fish and other small animals. They can eat organic matter and thanks to their filter feeding, rotifers contribute to the removal of suspended organic particles, the purification of freshwater bodies from pollution, and the maintenance of biological balance in the aquatic environment.

Anatomy & physiology

In the head part of the body, the rotifer has two lobes equipped with cilia, which resemble two rotating wheels. This system is called the wheel organ or corona. Using the cilia on the lobes, the rotifer creates a water flow that brings food particles to its mouth. The rotifer’s diet includes both plant and animal food: algae, bacteria, small protozoa, as well as suspended nutrients, such as leftover fish food. At the same time, the corona allows the rotifer to move quickly over considerable distances.

Dangerous to fish?

Rotifers pose no danger to aquarium fish. However, many aquarium enthusiasts, seeing a rotifer for the first time under a microscope, mistake it to be one of the dangerous fish parasites – a skin fluke.

Differences between Philodina and Gyrodactylus

The body shape of the rotifer is similar to that of a skin fluke with the opposites reversed. The way of moving on the substrate like a caterpillar is also characteristic of both microorganisms. But if we examine the skin fluke’s attachment disk, the haptor, and Philodina’s foot, we will see significant differences. The haptor of the skin fluke has a pair of central large hooks and a row of small hooks around the disk. Philodina, on the other hand, has a muscular tail with a pair of protrusions at the end. And, above all, the structure of the head is different.

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