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Would the drop remain suspended in one location or would it slowly spread out?
Nematodes in Fisheries
Important fish parasite- capillaria, camallanus
Nematodes are the most numerous multicellular animals on
A handful of soil will contain thousands of the microscopic
worms, many of them parasites of insects, plants or animals.
There are nearly 20,000 described species classified in the
In size they range from 0.3mm to over 8 metres.
Common parasite of both Marine and Fresh water
Although parasitic nematodes can infect almost all
organs in a fish, the majority of the currently known
species have been described from the intestine.
Adult worm in the ovary
. Liverwith encysted, anisakid,
A typical nematode is elongate and
cylindrical in cross-section.
Both the larval and adult stages of
nematodes parasitise fish, and
numerous species have been reported
from native fish species,
including Spinitectus from Murray cod
Nematodes will infest all types of
tissues and organs.
Nematodes are not often reported as
being a serious problem in farmed fish.
Head region of the
from Murray cod
Phylum – Nematoda
Class - Adenophorea Secernentea.
Families- Dioctophymatidae, Camallanidae
i. Adenophorea consist mostly of free-living
marine and freshwater species, as well as
terrestrial soil nematodes with only a small
number of parasitic organisms
ii. Secernentea also have free-living taxa, but
the vast majority of this class are parasitic
Classification of the Nematoda
Secernentea Rhabdita Camallanida Diplogasterida
Strongylida Ascaridida Spirurida
Shape •Elongated, cylindrical;
Sexes Separate (diecious
Head space •No suckers ,no hooks.
Well developed buccal
capsule in some
Alimentary canal •Present and
Body cavity present
Generally elongated worm with cylindrical body tapering at the
both ends - fusiform shape
Most fish nematodes are a whitish to tan color
Some are Reddish due the color of Pseudocoelomic fluid
•Pseudoterronova larvae – own heamoglobin
•Camallanus sp – from feeding on host blood
Swim bladder worms ( Anguillicola ).
Dark color is due to feeding on blood
The cuticle of nematodes
is elastic, and it is thick in gut-dwelling species (Hysterothylacium,
relatively delicate in histozoic specimens (Philometra rischta,
• some have row of spines on their cuticle
Body wall lacks Circular muscle
Body covered by Collagenous Cuticle shed periodically in life of
nematodes by Ecdysis
The cuticle are without cilia.
•Mouth have lips may prominent in later larval stages and reach their
full expressions in adult
The structure of the mouth shows
It may be a simple slit-like opening at
the anterior end surrounded by
distinct or indistinct papillae
(Capillaria, Philometra), but it can
form large labia or cuticular
outgrowths (Fig) called Interlabia
The mouth leads into the buccal capsule
(Figs12.7and12.8),which can be sclerotized and
furnished with large denticles, ridges, plates or tridents
(Camallanus, Cucullanus, Skrjabillanus, Anguillicola).
Some have teeth guarding
the rim of mouth
Most of them posses sensory
structures such as papillae that
surround the mouth and the
anterior end which serve as
The male reproductive organ usually
consists of testis, vas deferens,
seminal vesicle and ductus
The ejaculary duct, opening into the
cloaca, has some accessory copulatory
The most common accessory organs
are the sclerotized spicules.
Mostly 2 Spicules
The female reproductive organs are composed of ovaries, oviducts,
uteri, vagina and vulva.
In Capillaria and Raphidascaris spp - the vulva is found in the first
part of the body length,
but in Camallanus and Rhabdochona spp -posteriorally.
The Capillospirura -at mid-length.
In adult Philometra spp -the vulva and vagina are absent
They do not have protonephridia, respiratory organs or blood
Female nematodes are usually larger than males
Most fish nematodes are Oviparous
Nematodes have been characterized as a tube within a
tube; referring to the alimentary canal which extends from
the mouth on the anterior end, to the anus located near the
excretory system, and
but lack a discrete circulatory or respiratory system
The Nematode Body
The phrase tube-within-a-tube is
a convenient way to think of
nematode body structure, and
also a term used to refer to a
major trend in the evolution of
triploblastic metazoa .
It refers to the development of a
fluid-filled cavity between the
outer body wall and the
Nematodes have 3 cell layers
Ectoderm-Outer tissue layer(epidermis)
Mesoderm- middle muscle tissue layer(muscle)
Endoderm- innermost tissue layer(body cavity)
Body covered in a complex
(B) pseudocoelomate, and
The nature of this body cavity has led
to the grouping of metazoa into three
pseudocoelomate, and eucoelomate .
Nematodes are traditionally grouped
together as pseudocoelomates.
Because they have internal cavity that
is not lined with peritoneum.
Therefore it is not a “true” coelom
Male nematodes are usually smaller than their female counterparts.
Basic male reproductive structures include: one testis, a seminal vesicle and
a vas deferens opening into a cloaca.
One testis is most common, but two testis are found in some species, while in
others one testis is reduced.
Spermatogonia are produced in the testis and stored in the seminal vesicle
until the nematode mates.
The presence of one or two
copulatory spicules helpdialate
the vulva and can also serve as a
canal for the spermatozoa.
The spicules are made from
hardened cuticle, terminating in
sensory dendrites near the tip.
Often the body wall around the
cloaca is modified into a bursa,
which helps orient the male
nematode and then helps hold the
two nematodes together.
Spermatozoa are amoeboid, and
can have many different
Some spermatozoa are round to
ovoid in shape while others bear a
resemblance to flagellated sperm.
Different types of spermatozoa
characterize different taxonomic
groups of nematodes
The basic female structure includes:
one or two ovaries,
uteri, ovijector and
The ovary produces oogonia, which later develop into oocytes.
The seminal receptacles, sometimes developed into a
spermathecea, stores the spermatozoa until they are needed to
fertilize an ooctye.
The fertilized oocyte then develops into an egg in the uterus.
The uteri often ends in an ovejector.
The ovijector is very muscular and uses body movement combined with the
high internal body pressure of the nematode to expel the egg through the
All nematodes lay eggs.
Syngamy, or cross fertilization, is
common in most nematodes.
Hermaphroditism also occurs, with
the nematode gonads producing
spermatozoa first and storing them
until the eggs are produced.
Parthenogenesis is also a normal
means of reproduction in some
Nematodes laying eggs
The Digestive System
The nematode digestive system
is generally divided into
The stomodeum consists of the
mouth and lips
buccal cavity, and
the pharynx (esophagus).
Each of these regions are used
extensively in taxonomy and
classification of nematodes, as well as
providing as indication of feeding
habit or trophic group.
For example, the buccal cavity of plant parasitic nematodes (and
some insect parasites ) is modified in the form of a hollow spear,
adapted to penetrate and withdraw the contents of host cells.
Predaceous nematodes often have a buccal cavity characterized by
teeth or hook-like projections. The buccal cavity of bacterial
feeding nematodes is relatively unadorned.
The oesophagus and buccal cavity is lined with cuticle
The proctodeum (back ectodermal part of an alimentary canal)also
lined with cuticle.
The intestine streches from the oesophagus to proctaodeum and is
simple tube like structure.
The digestive system works when food is secreted by different
enzymes found in the glands in the esophagus.
Afterwards, it is then sent through the oesophagus to the intestine
Like many living things, nematodes exchange gases with the atmosphere.
However, unlike many living things nematodes lack a formal respiratory
The respiratory system is responsible for performing gas exchange.
• In mammals and reptiles, this system consists of trachea, lungs and
•In the respiratory system of fish the dominant feature is gills.
Nematodes do not possess any of these organs, instead, nematode
respiration works in a much more simplistic manner. We will examine this
in the next slide.
Nematode respiration relies on a process calleddiffusion.
Diffusion is when molecules, in this case gas molecules, move from
an area of higher concentration into an area of lower concentration.
For example, what would happen if
you placed a drop of blue food
coloring into a glass of water? Think
The answer is that the drop would slowly spread throughout the
glass until all the water was tinted blue.
This simple example demonstrates diffusion in that the drop
initially had a high concentration of blue dye and the water had a
The blue dye then moved from the area of greater concentration
(the drop) into an area of lower concentration (the water), thus
precisely modeling our definition of diffusion
Here you'll notice a picture of the
body layout of a nematode.
Now, with respiration we're primarily
concerned with two
gases, oxygen and carbon dioxide.
Oxygen is the primary gas animals
inhale for use in respiration.
Carbon dioxide is a waste product of
respiration, and is the primary gas
Now notice where the greater
concentrations of each gas reside
within the image.
The circulatory system is
obviously not present in the
organisms in this phylum,
therefore, the species in this
phylum obtain a pseudocoelom,
which is basically the body
cavity of any multicellular
organism filled with
superfluous amount of fluids,
and also transports the specific
nutrients, oxygen, etc.
The circulatory system
So, because there is an absent of the circulatory system, the
metabolic waste is excreted by two ducts that the species
The Excretory system
The nematode have a network of
excretory tubes, which transfer the
much of the solid waste to an anus of
The nematode is one of the simplest
creature to have two openings for
excretion, rather than one in similarly
The secreted / excreted
material from the canal and
gland cell passes through a
cuticle lined excretory duct
located just below the terminal
bulb of pharynx and is
deposited outside via the pore
at the ventral midline
Four distinctive cell types make up the excretory system
One pore cell
One duct cell
One canal cell(excretory cell)
Fused pair of gland cell
The worms also release salt through the
There are two ways to release this
based of the nature of the worm.
Parasitic worms tend to have a
glandular process to excrete, while
nonparasitic worms tend to have a
much more tubular method of releasing
their salty waste
Life cycles differ depending upon the species of nematode.
Organisms that contain the reproductive adult stages of nematodes are
known as final or definitive hosts.
Organisms that are required for the completion of a nematode life cycle
but do not contain the final reproductive adult stage are known
as intermediate hosts.
Indirect life cycle where the fish is the final (definitive) host.
The nematode eggs/larvae (a) enter an aquatic invertebrate intermediate
host (b), such as a copepod, tubifex worm, or insect larva, prior to being
eaten by or entering the final host fish (c).
In direct life cycle
it does not need
host and infection
can spread directly
from one fish to
ingestion of eggs
Some nematodes have the ability to survive in "alternative"
organisms, known as "paratenic" hosts.
These hosts are not required for completion of the life cycle but they
can contain infective nematode life stages and be a source of infection .
They can be fish, worms or other aquatic organisms that eat the
nematode eggs or larvae
Large round worm
Commonly found in the gut of angel fish
Often recognised by its double
operculated eggs in the female worm
The Capillarids as a group can infect a
wide variety of fish hosts.
Capillaria pterophylli is a relatively
common nematode seen in the
intestines of cichlids (including
angelfish and discus).
Capillaria species are also seen in
cyprinids, gouramis, tetras and other
species of fish.
Capillaria females are easily identified
when they are carrying the brown,
barrel-shaped eggs with a plug-like
structure on each end
Capillaria species have direct life cycles, and can spread from
one fish to another by ingestion of infective larvae.
It may take Capillaria pterophylli eggs up to three weeks at 68-
73°F (less time at warmer temperatures) before they contain
embryos developed enough to be infective when ingested by a
The length of time required from infection until the mature
adult parasites are producing eggs or larvae is approximately
three months at these temperatures.
Even though Capillaria species have direct life cycles, a tubifex
worm may act as a paratenic (alternative) host and "carry"
infective stages of Capillaria to the fish that consumes them
Capillaria species are relatively transparent ,
if only immature or male nematodes are present, they may be easily missed
However, Capillarid infection is relatively easy to diagnose when females
containing the typical barrel-shaped eggs with a polar plug on each end
(opercula) or eggs alone are present in the intestinal tract.
Capillarid infections can be treated
with dewormers such as
levamisole or fenbendazole .
To avoid reinfection, organic debris
and feces should be removed as often
as possible, especially following
Brood stock should be evaluated for the presence of nematodes
prior to use and periodically throughout the breeding period.
Proper sanitation will help prevent the spread of nematodes and
reduce infection loads.
Live foods, such as oligochaete worms (e.g., tubifex worms), may
act as carriers, and their use should be avoided if possible
tubifex worms – live fish food
Capillaria philippinensis is a parasitic nematode which
causes intestinal capillariasis
The natural life cycle of C. philippinensis is believed to involve fish
as intermediate hosts, and fish-eating birds as definitive hosts.
Humans acquire C. philippinensis by eating small species of infested fish
whole and raw
Longitudinal section of
an adult C.philippinensis
from an intestinal Biopsy
specimen stained with
Although C. philippinensis infections are rare, it can serve as an indicator
that one is being exposed to raw or undercooked fish.
Worms create infection by penetrating the mucosa of the small intestine
and reentering the lumen.
As they progress into the body, they cause the mucosa and submucosa to
Infected people can have abdominal pains, diarrhea, weight loss, weakness,
malaise, anorexia, and emaciation.
They also experience loss of proteins and electrolytes and malabsorption of
fats and sugars.
If symptoms and the number of worms increase, it can eventually lead to
Camallanus species infect the gastrointestinal tract of cichlids, live-
bearers (including guppies and swordtails), and other species of
Usually, the first evidence of infection is a red, worm-like animal
protruding from the anus of a fish
Camallanus species have indirect life cycles and are live-bearing
They are considered "ovoviviparous" ("ovo" is the scientific term
for "egg" and "viviparous" means live-bearing), as females
incubate the eggs which hatch into larvae within their bodies
Close up of a Camallanus sp. female showing larvae inside.
These larvae are excreted into the
water with the fish's feces and are
ingested by a copepod or other
Within the copepod, the larvae
develop further into a third-stage
After the copepod, containing the
third-stage larvae, is eaten by the
appropriate fish host, the larvae
migrate out into the fish, develop into
reproductive adults, and the life cycle
Camallanus species can be identified by their red color.
Their location further toward the posterior of the intestinal tract
than other worm-like parasites (typically very near, and often
protruding from, the anus of the fish).
The presence of a buccal capsule (mouth structure) that is divided
into two lateral valves, giving the mouth a slit like appearance;
and, if gravid females are present, the presence of both eggs and
larvae within their bodies.
Because Camallanus nematodes are located within the intestinal
tract, common dewormers should be effective.
As a copepod or other crustacean host is required to complete the
life cycle, avoiding the use of copepods or related crustaceans as
food items will help reduce potential for infection.
Evaluation of brood stock for the presence of parasites prior to use
will also aid in identifying carriers.
The pathology induced by the nematode Camallanus cotti in the aquarium
fishes Beta splendens (beta fish) and Poecilia reticulata (guppy) consisted of
gross and microscopic lesions,
In beta fish it is characterized by
abdominal swelling with reddish parasites
protruding from the anus in both fish hosts
similar in the beta fishes and guppies,
a few glandular elements, and
extensive erosion areas in the rectum mucosa,
with a marked thickening of the wall and
absence of inflammatory infiltrate.
Eustrongylides is a nematode that uses fish as its
intermediate host. The definitive host is a wading bird, a
common visitor to ponds. The worm encysts in the peritoneum
or muscle of the fish and appears to cause little damage.
Because of the large size of the worms ( Figure ), infected fish
may appear unsuitable for retail sales.
Target Tissues: Internal tissues
Appearance: Grossly visible; coiled,
reddish worm (encysted)
Size: Larvae (found in fish) 11-83 mm
Movement: Movement usually not
seen in fish
Eustrongylides species can be found in muscle, “free” within the
body cavity, or encapsulated on the liver and other organs, but they
are found outside the intestinal tract of fish.
Eustrongylid nematodes can affect a number of different species, including
danios, and angelfish.
Affected fish typically have bloated
abdomens (dropsy), as the
nematodes frequently migrate into
the body cavity from the gut and can
be quite large.
Eustrongylides species have complex, indirect life cycles.
Adult Eustrongylides tubifex and other Eustrongylid nematodes are
found in fish-eating birds.
The eggs are shed by the birds into ponds, where they develop into
a life stage that is consumed by an oligochaete worm, such as the
Within these tubifex worms, the nematodes develop still further
into a third larval stage, known as an "L3", which is the life stage of
the Eustrongylides group that can infect fish when eaten.
Once the tubifex worm containing the L3 stages is eaten by a fish
and digested, the nematodes migrate (within the fish) into the
body cavity and, frequently, over the external surface of internal
organs such as the liver.
The eggs of all Eustrongylides
species are very tough and
can easily survive for
some time in fish ponds.
At about 77°F, it can take anywhere from three months to four and one-
half months from the time the bird infects the pond
with Eustrongylides eggs until the time fish become infected
After this 3-4 month period, fish raised in ponds with a
population of fish-eating birds have an even greater chance of
becoming infected as the number of nematodes increases over
As Eustrongylides species infect areas outside the gastrointestinal tracts of
fish, necropsy of a small group of affected fish is the only sure method to
During necropsy Eustrongylides species, such as E. tubifex, are easily
identified from their location in the fish (encysted in mesenteries of the
body cavity or in muscle), their red coloration, and their relatively long
bodies (11-83 mm);
however, there are other nematodes that may appear similar
so positive identification will require examination by a veterinarian, other
fish health specialist, or parasitologist.
Other than mechanical removal, there is no effective treatment for
these nematodes due to the location of the larvae within the coelomic
cavity or in the muscle.
Culling affected fish is recommended.
Removal of the final host (fish-
eating birds) or any intermediate
hosts (tubificid worms or other
oligochaetes) will help reduce the
Sanitation of ponds or tanks will
help remove any intermediate
Sanitation of ponds at the very
minimum of once or twice a year
Parasites of freshwater tropical fishes
No genera associated with freshwater tropical fishes.
Eustrongyloides- encysted in muscles
Capillaria- frequently found in FW
Camallanus- Guppies and swordtails seem to be most frequent
Adult & larval forms – in lumen of intestine
Free migratory forms – peritonieal Cavity
Encysted forms – in musculature
Heavy and moderate infections with
Anguillicola crassus in opened swim
bladders of European eels
Parasites of marine tropical fishes
Crustaceans – 1st intermediate host
Ascaridoidae- Anisakis, Contracaecum, Terranova
Spiruroidae – Ascarophis, metabronema
Camallonoidae- Aslanus, Camallanus
Dracunuloidae- Philometra, philonema
Philometra oviata in gudgeon
Heavy infestation reported in White spotted puffer fish from Hawaiian waters
Parasites of Elasmobranch
•Very small no
•Only 68 sp
Most belongs to 2 families
1. Heterocheilidae of order Ascanididae
2. Cucullanidae of the order of Spiruridae
Primarily in digestive tract
visible nodules on the exterior of the intestion
Nematodes of shark require atleast one intermediate host usually
Second intermediate host – fish (Pleuronectidae, Gadidae)
Fish disease and Disorders Volume 2 by P.T.K. Woo
Fish pathology – 4 th edition By Roberts
Introductrion to Freshwater Fish Parasites by RuthEllen
Klinger and Ruth Francis Floyd
Fish Disease- Volume 2 By Jorge C.Eiras , Helmut Segner,
Thomas Wahli, B.G. Kapoor
Fish Disease diagnosis and treatment by Edward.J.Noga
Marine parasitology Edited by Klaus Rhode