Ichthyophthiriasis: White Spot Disease

PRESESNTED BY : ANJALI BALA NAIK
DEPARTMENT OF FISH PATHOLOGY AND HEALTH
MANAGEMENT
FISHERIES COLLEGE AND RESEARCH INSTITUTE
TAMILNADU DR J. JAYALALITHAA FISHERIES UNIVERSITY
ICHTHYOPHTHIRIASIS

INTRODUCTION
Ichthyophthirius multifiliis is an ectoparasite of freshwater fish
which causes a disease commonly known as white spot disease,
or Ich.
Ichthyophthirius multifiliis was first named by Fouquet (1876).
The Latinized species name multifiliis means “much” plus
“daughter”, because a large number of offspring, namely
theronts, are produced by an encysted tomont in the free-living
stages.
Disease caused by Ichthyophthirius multifiliis ,is characterised by
presence of white spots all over the external body surface(skin ,
fin, gills).

LIFE STAGES
The direct life cycle of parasite
require only one host and the life
cycle generally divided into three
stages:
1) the on-fish, feeding trophont;
2) the environmental, reproducing
tomont;
3) the infective, fish-seeking
theront

Feeding stage :
The trophont invades and encysts
between the thin outer layers of the fish
host’s skin and gills in order to feed on
those tissues. Because of the covering by
this epithelial tissue and mucus, the
trophont stage is protected from
chemical treatment. Once the trophont is
mature, it stops feeding, leaves the fish,
and becomes a tomont.
Reproducing stage:
Tomont( encapsulated dividing stage)
quickly secretes a gelatinous-walled
outer cyst that allows it to stick to
surfaces in the environment. The tomont
begins to divide quickly, forming
hundreds of new “daughter” parasites
(tomites) within a single cyst. The
gelatinous wall of the tomont cyst
protects it and the daughter tomites
from chemical treatment. The tomites
develops as theronts within the tomont
cyst. Following a period of days (warm
water temperatures) or weeks (cool
water temperatures)

Infective stage:
The theronts bore out of the tomont
cyst and become free-swimming,
infective parasites in search of a fish
host. These infective theronts must
find a live fish to complete the
parasite’s life cycle.
This free-swimming phase is
unprotected and, therefore, highly
susceptible to chemicals. Treatment
protocols should be designed to
target this theront stage.
This life cycle is highly dependent on
water temperature, and the entire
life cycle takes from approximately 7
days at 25 °C (77 °F) to 8 weeks at 6
°C (43 °F).

Epizootiology of ichthyophthiriasis
In the whole life cycle, I. multifiliis in the epithelia can activate the
immune response of its host, while theronts and tomonts are
affected by a variety of factors in the aquatic environment.
Theronts are active in free-swimming style seeking out their host
after released from a tomocyst, but in this stage, they are
vulnerable with lifespan less than 48 h at 20°C as usual.
The physical and chemical factors in water environment, such as
PH, water hardness, ion strength, salt concentration and
temperature, directly influence the life of I. multifiliis in
nonparasitic stage.

It was reported that high hardness water (120 mg l ) and PH (9)
were appropriate conditions to the life and infection of I. multifiliis
in external environment
The appropriate temperature for ichthyophthiriasis outbreak was
around 20°C with Danish geographic strains (Buchmann and
Bresciani 1997), while elevated temperature up to 30°C would
drive trophonts out of their host fish
. It has been demonstrated that temperature affected the
developmental rate of I. multifiliis in both parasitic and
reproductive stages. (Aihua and Buchmann (2001) recorded the
relationship between temperature and I. multifiliis development.)

Being unicellular organism in the niche of freshwater, I. multifiliis
is sensitive to salinity. The reproduction time of tomocyst
increased and the number of its offspring decreased at the
salinity of 5 parts per thousand (ppt), and salinity above 5 ppt
totally inhibited the tomocysts development (Aihua and
Buchmann 2001).
 Sodium chloride is therefore used to control ichthyophthiriasis
in aquaria, but for field use, the dose is too massive to afford for I.
multifiliis control.

The classic sign of an “Ich” infection is
the presence of small white spots on
the skin or fins .
These spots are caused as the adult
parasite (trophont) penetrates and
creates a space in the outer layers of
the fish’s body surfaces (epithelium) in
order to feed on the fish and move
around. These lesions look like small
white dots, blisters, or salt grains on
the skin or fins of the fish. The white
spots may not be as obvious on fish
that are white or pale in color, or if the
infection is limited to the gills. By the
time the white spots are visible to the
naked eye, the infected fish is very sick.

Typical behaviors of clinically infected fish before white spot
formation includes
Anorexia (loss of appetite, refusing all food, with consequential wasting)
Rapid breathing
Hiding abnormally
Not schooling (in schooling fish)
Resting on the bottom
Flashing (Rubbing and scratching against objects)
Upside-down swimming near the surface
The foci of infection become thickened and necrotic, then ruptured and
ulcerative, falling of necrotic skin and scales off the surface often occurs if fish
is seriously injured. Injury in the gill is usually more severe than the skin and
directly impacts respiration in fish (Majeed et al. 1984).

The trophont is not visible to the naked eye until it has fed on the fish and grown
to one or two millimeters. A trophont attached to the gills is hard to see.
Skin
Visible Ich lesions are usually seen as one or several characteristic white spots on
the body or fins of the fish. A smear should show ciliates if white spot is present.
Histopathological section of skin of freshwater fish shows I. multifiliis trophozoite

Eyes
The eye becomes cloudy almost to the point of whiteness and
the fish lose vision. Treating this condition requires an
investigation of water quality. When the water quality is suitable,
the fish will usually recover by themselves within one to two
weeks. Thus, it is advisable to wait for that time to elapse before
administering antibiotics.
Gills
If the parasite is only present in the gills, white spots may not be
seen at all but fish will die in large numbers. In these fish, gills
will often be pale and very swollen. Gill infection may cause
breathing at the surface and fast respiration.
Gill examination may reveal numbers of white spots or wet
mount of a gill from a biopsy may reveal the trophonts. The
fishes' breathing can slow, causing them to rest on the sand or
gravel.

Pathology
How Ich kills fish is not exactly known, however observations give
possible explanations.
When Ich infects the gills, the outer layer of the gills become
inflamed, restricting the flow of oxygen to the blood. The
respiratory folds, lamellae, become deformed, further reducing
the transfer of oxygen. The sheer numbers of Ich organisms
attached to the gills can mechanically block oxygen transfer.
The outer lay of gill cells may separate and result in loss of fluids,
making the fish struggle to regulate water concentration in the
body. Secondary bacterial and fungal infections are common
when the fish is impaired from the parasite.

Diagnosis
The diagnosis of "Ich" can easily be confirmed by microscopic examination of
skin and gills. Remove several "white spots" from an infected fish, then mount
them on a microscope slide with a few drops of water and cover with glass.
The most characteristic features of the mature trophont stage of the parasite
are large and dark (due to thick cilia covering the entire cell). continual rolling,
amoeboid motion and a horseshoe-shaped or C-shaped nucleus, measures 0.5
to 1.0 mm in size both of which are easily recognized during a microscopic
examination of infected tissue.
It is sometimes visible under 100x or 40x magnification. The adult parasite
moves slowly by tumbling.
The immature, free-swimming theronts are smaller, pear- or spindle-shaped,
translucent, and move quickly, continuously spinning on its longest axis as it
swims.

Theronts can resemble other parasites (especially Tetrahymena), so if only this
juvenile stage is seen, prepare a second slide and examine it closely for the
trophont stage to confirm the diagnosis. Because one “Ich” organism produces
hundreds of individuals in one generation,

Treatment
Any treatment method must take into account the species
of fish (some will not tolerate certain medications), how
many of the fish are affected, and the size and kind of
environment.
The first line of treatment for severe outbreak is usually
formalin or malachite green, or a combination of the two.
Copper, methylene blue, and baths of potassium
permanganate, quinine hydrochloride, and sodium chloride
(aquarium salt) have also been used but do not appear to
offer an advantage over the more readily available formalin
and malachite green products.

Total fish removal
Theronts, the motile and fish-infecting stage of the Ich life cycle, exit from the
tomont that burst at the bottom of the tank. Without fish to re-attach to,
however, theronts will die within 48 hours of exiting their tomont.
Heat treatment
Heat treatment can be highly effective, and it can be combined with other
treatments. Temperature affects how quickly the parasites multiply, so
increasing the temperature can force them through their life cycle more
quickly, allowing treatments to target Ichthyophthirius in its theront stage.
Also, higher temperatures around 86 °F (30 °C) can prevent tomont replication.
However, it can only be used on fish that can tolerate high water
temperatures, and is unsuitable for cold water fish like koi and goldfish, but
even in those cases, a higher water temperature will accelerate the life-cycle of
the parasite, allowing other treatments to take effect sooner

Salt
Aquarium salt at 3-5 grams/liter for two weeks can be used to
treat mild infections of Ich. Be aware that some soft water species
and some catfishes can be more sensitive to salt.
Chemical treatments
Copper is another common and effective treatment for this
parasite. However, two facts are essential to know prior to using
in an aquarium. The recommended dosage is 0.15-0.3 mg/L and
the concentration should never exceed 0.4 mg/L. Also, copper is
noticeably more toxic to fish in soft water than in hard water. The
combination of these facts makes it a poor choice for the average
aquarium hobbyist.

Methylene blue is commonly available for aquarium stores.
Despite its effectiveness against external protozoan
infections, it is now considered an outdated medication due
to its effects on beneficial bacteria, causing toxic ammonia
and nitrite levels.

Prognosis
When Ich is diagnosed early, effective treatment is used, and stresses
are minimized, mortality rates can be low.
However, if the infection is at an advanced stage, treatment protocols
are not followed, and the fish are stressed, higher death rates will occur.
When a fish has had Ich eradicated, it may develop partial resistance to
reinfection.
Partially treated fish may initially harbor low numbers of unseen
trophonts, often in the gills. This sub-clinical carrier will cause another
outbreak weeks later, most likely when stresses occur, or uninfected fish
are introduced to the aquarium.

Prevention
In preventing infection, priority should be given to avoid introducing the parasite
in the first place.
New tropical fish should be quarantined for at least four weeks and cold-water
fish for eight weeks. Also, washing your hands before and after maintenance of
each tank and using separate equipment will reduce the chances of spreading the
parasite between tanks.
New plants should be washed in lukewarm water and quarantined for several
days. During quarantine, plants can be treated with a plant disinfectant or a mild
broad-spectrum anti-parasitic remedy. Alternatively, the plants can be dipped in a
weak (pale pink) solution of potassium permanganate for several minutes, rinsed
with running water and added to the aquarium.
Prevention of the disease by vaccination is not possible, although several studies
identified potential vaccine candidate proteins, i.e. i-antigens, of the parasite.
Fish that survive an Ich infection may develop at least a partial immunity, which
paralyzes theronts that attempt to Infect it.

Ichthyophthiriasis: White Spot Disease

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Ichthyophthiriasis: White Spot Disease

Similar to Ichthyophthiriasis: White Spot Disease (20)

Recently uploaded

Recently uploaded (20)

Ichthyophthiriasis: White Spot Disease