On 9 Jun 1997 20:26:26 GMT, "Jolyon Claridge"
<Jac.Ullstrout at btinternet.com> wrote:
> I own a trout farm in the north west of England.
>Due to the low rainfall in recent years conditions of low water levels have
>caused an escalation in the number of cases of eye fluke in my stocks of
>rainbow trout. Does anyone have any information concerning: 1. Prevention
>of the condition. 2. Lifecycle of the parasite and whether it is
>particularly virulent under certain conditions. 3. Whether there is any
>cost effective method of treating fish which are already infected.
> Any help would be grately appreciated.
I will try to answer some of your questions:
1) Prevention: Depending on the size of your holding facility, it may
be possible for you to erradicate the snail population. One fairly
common way is (I believe) by using copper sulfate. This compuond is
highly toxic to snails.
2) Life Cycle: The common Eye fluke in Quebec Canada is known as
Diplostomum spathaceum. Its life cycle begins with an egg that is
deposited in water. After a period of embrionation it hatches into a
miracidium. This free swimming larval stage actively searches for
snails (the first intermediate host). Having found a snail, they
penetrate it and begin reproducing asexually. Begining some time after
infection the snails shed cercaria. These are also free swiming larval
stages. They basicsally suspend themselves in the water column waiting
for fish to swim by. By a yet unresolved method the cercaria penetrate
the fish and migrate to the eye (or maybe they penetrate the eye
directly?) by this time thaey have lost their tail and are known as
metacercaria (in fact they are known as diplostomulae, but these are
the functional equivalent to metacercariae). In the eye they will
either remain in the humors, or penetrate the lense (also
unresolved). They will "hang out" there awaiting ingestion by the
definitive host. In D. spathaceum's case this is a gull (Larus
delawarensis, L argentatus etc...).
In other words: The egg hatches, the miracidium penetrates a snail.
the snail sheds cercariae, the cercaria penetrate a fish to form
metacercaria. When the fish is eaten by a gull, the metacercaria
establishes in the gut of the bird and grows into an adult worm which
reproduces and releases eggs in the stool of the bird.
As for whether its virulence changes...Sorry I don't know.
3) Treatment. ...There is none that I know of, but I am no
I have a quastion of my own. Are you seeing fish mortality caused by
infection? Or is the problem purely on of people not wanting to
purchase fish with "cloudy" eyes?
I hope I was of some help.
Michael Levy Graduate student in parasitology
mikelevy at total.netmicha_l at alcor.concordia.ca