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I've done some reading and come up with some more info on Ergasilus -
They're also called gill maggots, because of the resemblance of the white
egg sacs to fly larvae. I have noticed that those on my fish are starting
to elongate and look more maggot-like, though very tiny. Apparently
temperature greatly affects their growth and reproduction.
According to the references I have, they are usually found attached to the
gills, gill covers and inside the mouth. Mine, however are primarily found
along the base of the dorsal fin. I haven't inspected the gills of my
fish. Supposedly, they do not often cause problems in home aquaria, but
can appear on newly imported fishes. Heavy infestations can cause severe
gill damage, emaciation, anaemia and death.
After eggs are released, they hatch in a few days and give rise to
juveniles that progress through several free-living stages. They then seek
out a fish to attach themselves to. After mating, the males die and drop
off. The females may remain attached to the fish for as long as a year.
They can overwinter on the host and not release eggs until the following
spring when water temps increase.
Organophosphates are recommended as a treatment for Ergasilus.
Metriphonate, trichlorphon and Masoten were mentioned. These are all
synonyms for the same insecticidal chemical, Dimethyl (trichloro
hydroxyethyl) phosphonate. A treatment of the tank or pond water at 0.25
ppm or 0.25-0.4 mg/liter is suggested. The material degrades rapidly in
warm, alkaline water, so the dosage should be refreshed every day until the
parasites are dead. Various references suggest continuous treatment over
periods from 2 to 10 days. In cool acidic water, the insecticide will
persist. This same treatment, by the way, is suggested for Lernaea. Skin
and gill flukes, leeches and other crustacean parasites are treated with
Some fish are considered sensitive to Metriphonate. Those mentioned were
orfe, rudd, piranhas and certain characins, as well as marine surgeonfish
and invertebrates. There are marine copepod parasites as well.
Due to it's instability in water, Metriphonate must be prepared from dry
powder prior to each dosing. It is a neuro-toxin and should be handled
with caution. Do not allow skin, eye or mucous membrane contact with the
powder or concentrated solutions.
A look through a supply catalogue found several products that claim to
treat copepod parasites: Aquatronics Discoworm, Paragon and Dyacide;
Aquarium Products Clout and Fluke-Tabs; and Kordon Trifon. Kordon Trifon
appears to be the best value at $2.99 for 4.5 oz of powder that will treat
464 gal. It's available from That Pet Place, 888-842-8738, Order number
Check out these books for more info:
Aquariology The Science of Fish Health Management Master Volume, John B.
Gratzek, Tetra Press
The Manual of Fish Health, Andrews, Exell and Carrington, Tetra Press
Parasites of North American freshwater fishes, Glenn L. Hoffman, Berkeley,
University of California Press, 1967
The afflicted sunfish seem to be perfectly healthy. A salt dip didn't
touch the Ergasilus. Maybe a longer dip would have done it, but the fish
were going nuts and looked like they were dying so I pulled them out after
Columbus Ohio USA <))><
mbinkley at earthling_net
Give a man a fish and you feed him for a day; teach him
to use "the Net" and he won't bother you for weeks.