This document defines key terminology used in fish parasitology. It discusses parasitology as the study of parasite-host relationships and fish parasitology as focusing on parasites of fish. Parasites are defined as organisms that live on or inside a host for food and shelter. They are classified based on host specificity (monoxenous, oligoxenous, polyxenous), number of hosts in their lifecycle (stenoxenous, heteroxenous), and location on the host (ecto, endo, haemal). The document also defines related terms like host, definitive host, intermediate host, reservoir host, vectors, and more.

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Terminology
in
Fish Parasitology

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Parasitology
The term ‘parasitology’ is originated from Greek word- ‘Para’ means beside, ‘sitos’ means food and
‘logus’ means study. It is the branch of science which deals with the study of the relationship between the
parasite and host. This discipline includes several approaches to the study of parasitic organisms such as
phylogeny, morphology, ecology, life history, physiology, chemotherapy, serology, immunology and bio
chemistry.
Fish parasitology
It is the branch of science that deals with the study of parasite of fishes. It includes the infection and
disease of fish caused by parasite.
Parasite
Parasite are those animal which cling to relatively large animals externally or internally for food and also
for completion of their life cycle. Among these two organisms, smaller one is parasite and larger one is
host. On the basis of host specificity, parasites are divided into three types:
1.Monoxenous parasites:
The parasites which are adapted for life in only one host species i.e. they are specific for it and
exhibit a strict specificity.
2.Oligoxenous parasites:
The parasites which can live in several hosts, even though one or more among them may be the
typical host.
3.Polyxenous parasites:
The parasites which do not have host specificity and being capable of infecting many hosts.
e.g. Ichthyobodo sp. infect all teleosts
On the basis of number of host for completion of their life cycle, parasites are divided into three types:
1.Stenoxenous parasites:
The parasites which complete their life cycle in a single host individual are known as stenoxenous
parasites.

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2.Heteroxenous parasites:
The parasites which require more individuals for completion of their life cycle are known as
heteroxenous parasites.
Heteroxenous parasites are also divided into two types-
A. Diheteroxenous parasites:
The parasites which have two hosts in their life cycle are called as diheteroxenous parasites.
e.g. Trypanosoma
B. Triheteroxenous parasites:
The parasites which have three hosts in their life cycle are called as triheteroxenous parasites.
According to the localization of the parasites in the body of the host, Parasites are also divided into three
types:
1. Ectoparasite: The parasites which live on external surface of the bodies of their host is called
ectoparasite. In fish, they are found on skin, gills and fins.
e.g. Dactylogyrus-Gill fluke-on gills of fish, Gyrodactylus-Skin fluke- on skin of fish
2. Endoparasite: The parasites which live in the interior of the host.
e.g. Ligula intestinalis live in visceral cavity of fish.
3. Haemoparasites: The parasites which live in the blood of the host animals.
e.g. some protozoan and nematode parasites
On the basis on dependency:
Permanent parasite: A parasite which permanently live in contact with its host, is called
permanent parasite.
Facultative parasite: A parasite which can live without a host is called facultative parasite.
Obligatory parasite: A parasite which cannot live without a host is called obligatory parasite.
Periodic parasite: A parasite which visits its host at intervals.

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Host
It is an organism which is physiologically larger than a parasite, belongs to a different species and provide
protection and supply nourishment to the parasite.
Definitive or final host
The host in which parasite reaches sexual maturity and reproduces its termed as definitive or final host.
e.g. aquatic bird in the case of Clinostomum
Intermediate host
The host which harbours the larval stages of parasite for development but not to reach sexual maturity is
known as intermediate host.
e.g. Fish in the case of Clinostomum
Reservoir host
When a host harbours a parasite till sexual maturity but tolerate the infection of the parasite, specifically
harmful to another animal and act as a source of infection of economically important animals is known as
reservoir host.
e.g. trash fish are source of infection of Ich disease. Dog is the reservoir host of Entamoeba species of
man.
Paratenic host
A host in which the immature parasite undergoes no development but remains infective to a definite host,
is called paratenic host.
e.g. Calyptospora funduli, the ingested sporozoites do not proliferate but undergo a kind of ‘maturing’, a
prerequisite for becoming infective.
Vectors
The hosts which carries and transmit the infective stage of parasite from one host to another are called as
vectors.
Host specificity
Host specificity can be defined as natural adaptability of a particular parasite to certain species or group
of host. Parasites can be very particular about which host species they will use.

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Antigen
an antigen is a molecule capable of inducing an immune response (to produce an antibody) in the host
organism. Sometimes antigens are part of the host itself in an autoimmune disease.
Antibody
An antibody ( Ab ), also known as an immunoglobulin ( Ig ), is a large, Y-shaped protein produced mainly
by plasma cells that is used by the immune system to neutralize pathogens such as pathogenic bacteria
and viruses . The antibody recognizes a unique molecule of the pathogen, called an antigen
Pathogen
in biology, a pathogen or a germ in the oldest and broadest sense is anything that can produce disease, the
term came into use in the 1880s. Typically the term is used to describe an infectious agent such as a virus
bacterium, protozoa, prion, a fungus, or other micro-organism.
Pathology
Pathology is a significant field in modern medical diagnosis and medical research, concerned mainly with
the causal study of disease, whether caused by pathogens or non-infectious physiological disorder.
Scolex
The knoblike anterior end of a tapeworm, having suckers or hook like parts that in the adult stage serve
as organs of attachment to the host on which the tapeworm is parasitic.
Probosics
The most common usage is to refer to the tubular feeding and sucking organ of certain invertebrates such
as insects (e.g., moths and butterflies), worms (including Acanthocephala, proboscis worms) and
gastropod molluscs.
Strobilla
Strobilla the chain of segments of a tapeworm
Larval parasite
An organisms parasitic larvae

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Corasidium
The ciliated first-stage aquatic embryo of pseudophyllid and other cestodes with aquatic cycles; within
the ciliated embryophore is a hooked larva, the hexacanth, which develops in the intermediate host, usually
an aquatic crustacean, into the next larval stage
Carcaria
The larval form of the parasite, it develops within the germinal cells of the sporocyst or redia. [4] A
cercaria has a tapering head with large penetration glands. [3] It may or may not have a long swimming
"tail", depending on the species. [4] The motile cercaria finds and settles in a host where it will become
either an adult, or a mesocercaria, or a metacercaria, according to species.
 Mesocercaria
A cercaria little modified but resting.
 Metacercaria
A cercaria encysted and resting.
Plerocercoid
Plerocercoid refers to last larval form, the infective form, found in the second intermediate host of many
cestoda with aquatic life cycles.
procercoid
The first stage in the aquatic life cycle of certain tapeworms, such as the pseudophyllideans (family
Diphyllobothriidae), following ingestion of the newly hatched larva (coracidium) by a copepod (water
flea). The procercoid develops into a tailed larva in the body cavity of the crustacean first intermediate
host; when the procercoid and its host are ingested by a fish, the procercoid enters the new host's tissues
and becomes a plerocercoid.
Sexual reproduction
Sexual reproduction is a form of reproduction where two morphologically distinct types of specialized
reproductive cells called gametes fuse together, involving a female's large ovum (or egg) and a male's
smaller sperm. Each gamete contains half the number of chromosomes of normal cells.

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Asexual reproduction
Asexual reproduction occurs when an organism makes more of itself without exchanging genetic
information with another organism through sex.
Parthenogenesis
Parthenogenesis a reproductive strategy that involves development of a female (rarely a male) gamete (sex
cell) without fertilization. It occurs commonly among lower plants and invertebrate animals
Spore
Spore a reproductive cell capable of developing into a new individual without fusion with another
reproductive cell. Spores thus differ from gametes, which are reproductive cells that must fuse in pairs in
order to give rise to a new individual.
Cyst
A cyst is a closed capsule or sac-like structure, usually filled with liquid, semisolid, or gaseous material.
Cysts usually occur within almost any type of the body's tissue; they vary in size from microscopic to
large structures that can displace internal organs
Hermaphrodite
A hermaphrodite is an organism with both male and female genitalia. In sexually reproducing organisms,
males have organs that produce male gametes, usually sperm. Females have different sexual organs that
produce female gametes, usually called eggs.
Dioecious
Dioecious having the male and female organs in separate and distinct individuals; having separate sexes.
 Direct life cycle
Parasitic life cycles occur in a variety of forms, all involving the exploitation of one or more hosts.
those that infect a single species have direct life cycles.
 Indirect life cycle
Parasitic life cycles occur in a variety of forms, all involving the exploitation of one or more hosts.
Those that must infect more than one host species to complete their life cycles are said to have
complex or indirect life cycles. those that infect a single species have direct life cycles.

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Fluke
A parasitic flatworm that has external suckers. Flukes are sometimes called trematodes.
Trematode
Parasitic flatworms or another name for fluke, taken from a Greek word that means having holes.
Worm
Any of various invertebrate animals having a soft, long body that is round or flattened and usually lacks
limbs. The term worm is used variously to refer to the segmented worms (or annelids, such as the
earthworm), roundworms (or nematodes), flatworms (or platyhelminths), and various other groups
Zoonosis
A zoonosis is any disease or infection that is naturally transmissible from vertebrate animals to humans.
Animals thus play an essential role in maintaining zoonotic infections in nature. Zoonoses may be
bacterial, viral, or parasitic, or may involve unconventional agents. As well as being a public health
problem, many of the major zoonotic diseases prevent the efficient production of food of animal origin
and create obstacles to international trade in animal products.
Epizoon
An animal that lives on the body of another animal, especially as a parasite.
Epizootic
Epizootic is a disease event in a nonhuman animal population, analogous 2n epidemic in humans.
Symbiosis
The living together in more or less intimate association or close union of two dissimilar organisms
Parasitism
It is defined as an intimate and obligatory relationships between two heterospecific organisms during
which the parasite, usually the smaller of the two partners is metabolically depended on the host.

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Phoresis
In biology, the term phoresis, also called phoresy, is an inter-species biological interaction in ecology and
refers to a form of symbiosis where the symbiont, termed the phoront, is mechanically transported by its
host. It is a type of commensalism; neither organism is physiologically dependent on the other.
Commensalism
Commensalism, in biology, a relationship between individuals of two species in which one species obtains
food or other benefits from the other without either harming or benefiting the latter.
The commensal—the species that benefits from the association—may obtain nutrients, shelter, support,
or locomotion from the host species, which is unaffected. The commensal relation is often between a
larger host and a smaller commensal. The host organism is essentially unchanged by the interaction,
whereas the commensal species may show great morphological adaptation. This relationship can be
contrasted with mutualism, in which both species benefit.
Mutualism
Mutualism association between organisms of two different species in which each benefits. Mutualistic
arrangements are most likely to develop between organisms with widely different living requirements.
Cleaning symbiosis
Cleaning symbiosis is a mutually beneficial association between individuals of two species, where one
(the cleaner) removes and eats parasites and other materials from the surface of the other (the client).
Cleaning symbiosis is well-known among marine fish, where some small species of cleaner fish,
notably wrasses but also species in other genera, are specialised to feed almost exclusively by cleaning
larger fish and other marine animals. Other cleaning symbioses exist between birds and mammals, and in
other groups.
Immunity
The ability of an organism to resist a particular infection or toxin by the action of specific antibodies.
Macrophage
Large cell capable of phagocytosis.

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Inflammation
A local tissue response to cellular injury marked by widening of blood capilaries, infiltration by white
blood cell etc.
Hyperplasia
An increase in the number of cell is called hyperplasia.
Metaplasia
Metaplasia is the abnormal change in the nature of a tissue.
Haemorrhage
Discharge of blood from the blood vessels, caused by injury is known as haemorrhage.
Anemia
Anemia is a decrease in the total amount of red blood cells (RBCs) or hemoglobin in the blood, or a
lowered ability of the blood to carry oxygen.
Chronic disease
An disease persisting for a long time or constantly recurring, of a very poor quality.
Acute disease
A disease or disorder that lasts a short time, comes on rapidly, and is accompanied by distinct symptoms.
Necrosis
The death of most or all of the cells in an organ or tissue due to disease, injury, or failure of the blood
supply is called necrosis

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Referrence
https://en.wikipedia.org/wiki/Fish_disease_and_parasite
http://www.wi-
afs.org/Portals/0/PDF/Training/FishParasitology.pdf
http://www.vetfolio.com/parasitology/parasitology-and-necropsy-
of-fish
https://www.fws.gov/policy/aquatichandbook/Volume_2/Chapter8
Parasitology.pdf
https://onlinelibrary.wiley.com/doi/10.1002/9781118222942.ch7
https://www.sciencedirect.com/science/article/pii/S0065308X0860
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