Those collected from Saginaw Bay, Lake Huron ranges in size from 0.6– 0.76 mm but in other regions it can reach 1 mm in length (Hudson and Bowen 2002).

The reproductive cycle of N. japonicus is rapid and output can be very high. Females and males probably mate once before females attach to their fish hosts. Spermatozoids can likely be retained for a period of diapause, for example over winter, so that egg development can occur later, for example in the spring. In a life time, females can produce a total of 1500–2000 eggs in 14–29 pairs of egg sacs. Sexual maturity is attained more quickly at temperatures of 30ºC than at 20ºC. Population levels are low during the cold winter months, but increase in the spring. After hatching, N. japonicus passes through 6 nauplius stages and around 5 copepodid stages before reaching the adult stage (Abdelhalim et al. 1993; Baud et al. 2004; Hudson and Bowen 2002; Urawa et al. 1980, 1990).

Emerald shiner (Notropis atherinoides) and Spottail shiner (Notropis hudsonius) are subject to a wild-capture baitfish fishery in MI, and Bluntnose minnow (Pimephales notatus) is approved for capture for personal use by anglers in MI. All three species can host N. japonicus, and capture and transport of them greatly increases the possibility of spreading the parasite to other water bodies, streams, and rivers (Hudson et al. 2011).

Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental	Socioeconomic

Realized:
Neoergasilus japonicus can cause infected fish to hemorrhage at the attachment site.

In Saginaw Bay, Lake Huron, N. japonicus has most commonly been found infecting Pumpkinseed sunfish (Lepomis gibbosus), followed in frequency by Yellow perch (Perca flavescens), Rock bass (Ambloplites rupestris), Bluegill (L. macrochirus), Carp (Cyprinus carpio), Channel catfish (Ictalurus punctatus), Goldfish (Carassius auratus), Green sunfish (L. cyanellus), Smallmouth bass (Micropterus dolomieu), Largemouth bass (M. salmoides), and Fathead minnow (Pimephales promelas) (Hudson and Bowen 2002).  In 2006, eight new hosts of N. japonicus were discovered in Saginaw Bay, including Bluntnose minnow (P. notatus), Common shiner (Luxilus cornutus), Emerald shiner (Notropis atherinoides), Golden shiner (Notemigonus crysoleucus), Quillback (Carpoides cyprinus), Sand shiner (Notropis stramineus), Spotfin shiner (Cyprinella spiloptera), and Spottail shiner (N. hudsonius) (Hudson et al. 2011).  

Potential:
Neoergasilus japonicus could disperse outside of known locations and and has the potential to do so relatively quickly. In 20 years, it probably moved across Europe, where it has been introduced to such countries as the U.K., Finland, France, and Hungary.  It is widely distributed and often associated with aquaculture. Within the Palearctic region, fish hosts are all cyprinids and percids. One of these is the Rudd (Scardinius erythrophthalmus), which has been introduced to and is established in Lake Ontario.  N. japonicus is not limited to cyprinids and percids within North America; infection of centrarchids and ictalurids has also been reported (Abdelhalim et al. 1993, Hayden and Rogers 1998, Hudson and Bowen 2002, Jansson and Karppinen 1988, Knopf and Hoelker 2005, Lescher-Moutoue 1979, Mugridge et al. 1982, Ponyi and Molnar 1969, Tuuha et al. 1992). It was discovered colonizing multiple threatened cichlids in Mexico (Suárez-Morales et al. 2010).

There is little or no evidence to support that Neoergasilus japonicus has significant socio-economic impacts in the Great Lakes.

Potential:
Neoergasilus japonicus has invaded aquaculture ponds outside of the Great Lakes and has demonstrated the ability to infect many types of farm-raised fish (Hayden and Rogers 1998). The impact of these invasions is unknown.

There is little or no evidence to support that Neoergasilus japonicus has significant beneficial effects in the Great Lakes.

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Control
Biological
There are no known biological control methods for this species.

Physical
Electron beam irradiation can be used to control microorganisms in aquatic pathways, including Neoergasilus japonicus (GLMRIS 2012). Electron beam irradiation is a non-selective control method which exposes water to low doses of radiation using gamma-sterilizers or electron accelerators, breaking down DNA in living organisms while leaving behind no by-products (GLMRIS 2012). Ultraviolet (UV) light can also effectively control microorganisms including N. japonicus in water treatment facilities and narrow channels, where UV filters can be used to emit UV light into passing water, penetrating cell walls and rearranging DNA of microorganisms (GLMRIS 2012).

Chemical
The Great Lakes and Mississippi River Interbasin Study (GLMRIS 2012) suggests that alteration of water quality using carbon dioxide, ozone, nitrogen, and/or sodium thiosulfate could be effective in preventing upstream and downstream movement of copepods. It should be noted that the effectiveness of these methods is likely significantly diminished against copepod ephippia.

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.