Prevention of "Ich"
Prevention of "Ich" is preferable to treating fish
after a disease outbreak is in progress. All incoming
fish should be quarantined for at least three days when
temperatures are 75 to 83°F. At cooler temperatures
a 3-day quarantine will be inadequate for "Ich"
because of its lengthened life cycle. For this reason,
and to prevent introduction of other diseases which
have incubation periods greater than 3 days, a longer
quarantine is strongly recommended. Three weeks is
generally considered a minimum period for adequate
quarantine of new fish.
Treatment of "Ich"
Control of "Ich" outbreaks can be difficult
because of the parasites' unusual life cycle and the
effect of water temperature on its life cycle. Review
the life cycle of L multifiliis presented in Figure 1 .
Of the life stages shown, only the free-swimming
tomites are susceptible to chemical treatment. This
means that application of a single treatment will kill
tomites which have emerged from cysts and have not
yet burrowed into the skin of host fish. This single
treatment will not affect organisms which emerge
after the chemical has broken down or been flushed
from the system. Repeated treatments, however, will
continually kill the juvenile tomites, preventing continuation of the infection. The epizootic will be
controlled as more adult parasites drop off the sick
fish, encyst, and produce young which cannot survive
because of the repeated application of chemicals.
This process will be greatly accelerated if organic
debris can be removed from the tank or vat following
treatment. This will remove many cysts from the
environment, decreasing the number of emergent
tomites.
Water temperature has a tremendous influence on
how fast the life cycle for "Ich" ( Figure 1 ) is
completed. At warm temperatures (75-79°F), the
life cycle is completed in about 48 hours, which
means that chemical treatments should be applied
every other day. At cooler temperatures the life cycle
is prolonged and treatments should be spaced further
apart. For example, at a water temperature of 60°F,
treatments should be spaced 4 or 5 days apart. In
warm water, a minimum of three treatments applied 2
to 3 days apart is required. In cooler water, a
minimum of five treatments should be applied 3 to 5
days apart. Treatments should never be discontinued
until all mortality from "Ich" has stopped. Fish should
be closely watched during recovery; the weakened
fish may be susceptible to a secondary bacterial
infection. The choice of chemical used to treat "Ich"
will be based upon water quality conditions, species
of fish to be treated, and the type of system fish are
housed in. In general, copper sulfate, formalin, and
potassium permanganate are all effective against
"Ich" when applied at the correct concentration in a
repetitive manner as described above.
