Page 4 - TBAS-may-2018

-4- TBAS May 2018 ....................

Introduction to the Ectoparasites
Ectoparasites are parasites which cling to the external surfaces of the fish
such as the gills, skin, and fins. Although ciliated protozoans often colonize the
external surface of fish, they generally do not feed from the body fluids or tissue
of the host, and they will not be treated in this article.
Parasitic crustaceans are relatively rare in comparison to the extreme-
ly common monogeneans: gyrodactylus and dactylogyrus which usually occur
together on discus. These monogeneans are externally parasitic hook worms
which attach to the skin or gills. They can be viviparous, meaning livebearing, or
oviparous, meaning egg laying. They are very significant parasites of fish which
cause extensive losses in commercial culture. They are extremely common
among aquarium and pond cultured fish and they have been cited as being the
number one killer of juvenile discus.
Fortunately, chemical treatment to eliminate them is relatively fast and
effective due to the fact that they live on the external surfaces of the fish where
water soluble chemicals can easily reach them. Treatment will have to be repeat-
ed, however, especially in the case of the egg laying dactylogyrus.

Monogeneans - Structure (Fig. 1)
These are usually ectoparasites possessing
one or more hooks in the rear of their body by which
means they attach themselves to the skin or gills of
the host fish. They may also possess chitinous sucking
discs. There are no intermediate hosts in the life
cycle. They all have an organ of attachment at the
posterior end known as a haptor which is equipped
with hooks and or clamps or suckers. They also usually
have another anchoring organ at the anterior end as
well (Roberts, 1989, p. 244).
They can produce either eggs or fully developed
offspring, and this can occur directly upon the host or
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