''Brooklynella hostilis'' is a

parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...

of marine fish, found in wild fish, farmed fish and aquariums. It is kidney-bean shaped, and approximately 60–80 μm long, with bands of

cilia The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike projecti ...

. ''B. hostilis'' is the only species in the

monotypic taxon In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...

''Brooklynella'', a genus in the order Hartmannulidae. It reproduces by binary fission. ''B. hostilis'' causes the disease Brooklynellosis, also known as slime-blotch or clownfish disease. In

marine aquarium A marine aquarium is an aquarium that keeps ocean, marine plants and animals in a contained environment. Marine aquaria are further subdivided by hobbyists into fish only (FO), fish only with live rock (FOWLR), and reef aquarium, reef aquaria. Fi ...

s, ''B.hostilis'' infects most teleosts (ray finned fishes). ''B.hostilis'' feeds on dead skin cells and can cause severe damage to gills. Affected fish have a gray discoloration, and may breathe abnormally fast or abnormally slow. The infection can cause sloughing of skin, and congestion of the gills. The parasite spreads rapidly, and can easily transfer to a new host. Formalin is an effective treatment.

References

Phyllopharyngea Parasites of fish Veterinary parasitology {{Alveolata-stub