Ergasilus

Ergasilus are parasites that infect fish and are very similar to the anchor worms both in regards to symptoms and treatment. Ergasilus has a long development time and seemingly healthy fish can therefore be infected as well. These parasites can often weaken fish and thereby invite other diseases to infect the already sick fish. Ergasilus are rarely a problem in aquaria but common on wild or pond cultured fish. Mature females are parasitic whereas immature stages and males are free-living. Ergasilids attach to their host by wrapping their modified second antennae around the filaments of the gills. Attachment and feeding of the parasite causes severe damage to gill tissue. Heavy infestations may result in secondary infections by fungi and bacteria, respiratory difficulties and ultimately death. Although Ergasilus has been reported from Australian native fish, to date there have been no reported severe outbreaks of this parasite on captive rainbowfishes in Australia.

This parasite can be treated using a potassium permanganate. Use 2 mg/L potassium permanganate if you want to treat the entire tank. A stronger solution at 10 mg/L is required to kill the Ergasilus using a single 20-30 minute bath. Diflubenzuron can be used at a concentration of 0.1 mg/L. An alternative to diflubenzuron is Lufenuron. Anecdotal reports indicate that this drug is effective for treating ectoparasitic crustaceans at a dose of 0.1–0.2 mg/L. Teflubenzuron is another drug that has been used to treat fishes.