Neobenedenia spp

From Fish
Japanese flounder parasitized by Neobenedenia spp
Eye infection of N. girellae in cobia
A stained specimen of N. girellae

The capsalid monogenean Neobenedenia melleni is a parasitic skin fluke of fish worldwide. Unlike most monogenean parasites, N. melleni is notorious for its lack of host-specificity.

In Japan, Neobenedenia girellae infections to cultured Japanese flounder and cultured tiger puffer were reported for the first time in 1991. It is considered that N. girellae was introduced from China since imported greater amberjack fry was infected with this parasite (prevalence up to 70.0 %) [1].

Neobenedenia spp are known to infect the following species of fish: Yellowtail (Seriola quinqueradiata), Greater amberjack (Seriola dumerili), Yellowtail amberjack (Seriola lalandi), Almaco jack (Seriola rivoliana), Tiger puffer (Takifugu rubripes), Japanese flounder (Paralichthys olivaceus), Red sea bream (Pagrus major), Japanese sea bass (Lateolabrax japonicus), White trevally (Pseudocaranx dentex), Leopard coaralgrouper (Plectropomus leopardus), Hong Kong grouper (Epinephelus akaara), Malabar grouper (Epinephelus malabaricus) and Cobia (Rachycentron canadum)

Clinical signs

The parasite (about 3-6 mm) is observed on the body surface. The lesion is erosive and the mucus is excessively secreted. Irritation by the parasite causes the affected fish to scratch their body on the net, resulting in the skin wounds.

N. girellae causes the retardation of growth following to low feeding. The lesion is eroded by attaching of the haptor and wounded by feeding of the parasite. Secondary infection occurs since bacteria invade through the wounding site resulted from the scratching on the net. Since this parasite is not infectious to human, it is harmless in food hygiene.


The parasite can be identified by morphological observation in a flattend preparation. Neobenedenia girellae can be distinguished from Benedenia seriolae, a monogenean infecting Seriola spp, by the morphology. B. seriolae is larger (body length 5-12 mm). Furthermore, the anterior structure between two suckers is concave and convex in N. girellae and in B. seriolae, respectively[2].


It is recommended to kill the parasites at the body surface by the freshwater-bathing for 5-10 minutes (longer when water temperature is low) and to regularly change the net for the purpose of removing the entangled eggs. Currently, bath treatments with a hydrogen peroxide solution and oral administration of praziquantel can be used to control the parasite. An acquired protection against secondary infection with the parasite was demonstrated in primed Japanese flounder[3].


  1. Ogawa, K., M. G. Bondad-Reantaso, M. Fukudome and H. Wakabayashi (1995): Neobenedenia girellae (Hargis, 1955) Yamaguchi, 1963 (Monogenea: Capsalidae) from cultured marine fishes of Japan. J Parasitol 81:223-227
  2. Kinami, R., J. et al (2005) A practical method to distinguish between Neobenedenia girellae and Benedenia seriolae. Fish Pathol 40:63-66
  3. Bondad-Reantaso, M. G., et al (1995): Acquired protection against Neobenedenia girellae in Japanese flounder. Fish Pathol 30:233-238