Fish diseases andFish diseases and
control measurescontrol measures
Sameer G ChebbiSameer G Chebbi
Dept. of ZoologyDept. of Zoology
Industrial fish and fisheriesIndustrial fish and fisheries
Karnatak Science College,Karnatak Science College,
DharwadDharwad

IntroductionIntroduction
 Like all other organisms, fish also get sick and isLike all other organisms, fish also get sick and is
affected by various kinds of diseases and pests,affected by various kinds of diseases and pests,
especially in the intensive and commercial fish culture,especially in the intensive and commercial fish culture,
resulting in huge loss to the farmers.resulting in huge loss to the farmers.
 Some of the diseases are epidemic and contagious andSome of the diseases are epidemic and contagious and
therefore, special precautions are needed to preventtherefore, special precautions are needed to prevent
them.them.
 Therefore, some basic theoretical knowledge about theTherefore, some basic theoretical knowledge about the
common diseases and their management practices iscommon diseases and their management practices is
essential for the growers to take precautions as well asessential for the growers to take precautions as well as
to treat the diseases.to treat the diseases.
 This knowledge is especially needed for the commonThis knowledge is especially needed for the common
people and the social workers who are promoting fishpeople and the social workers who are promoting fish
farming as an income generating programme among thefarming as an income generating programme among the
people.people.

 Fishes are infected by many disease causing organismsFishes are infected by many disease causing organisms
such as virus, bacteria, fungi, protozoa, nematodes, andsuch as virus, bacteria, fungi, protozoa, nematodes, and
internal parasites like tape worms, crustaceans etc.internal parasites like tape worms, crustaceans etc.
 Besides these, there are problems caused by harmfulBesides these, there are problems caused by harmful
insects, voracious fishes, amphibians, reptiles, birds andinsects, voracious fishes, amphibians, reptiles, birds and
mammals.mammals.
 In this chapter we will tried to enumerate the differentIn this chapter we will tried to enumerate the different
organisms causing diseases to the fishes, just to give anorganisms causing diseases to the fishes, just to give an
idea of the various sources and causes of diseases.idea of the various sources and causes of diseases.
 Each disease is very complicated and different fromEach disease is very complicated and different from
the other. Therefore, dealing with fish diseases is not asthe other. Therefore, dealing with fish diseases is not as
simple as people usually think.simple as people usually think.

 It is not possible to describe all the diseases that occurIt is not possible to describe all the diseases that occur
to the fishes as there are too many in number.to the fishes as there are too many in number.
 Only the most common diseases, that are affecting theOnly the most common diseases, that are affecting the
Indian and Chinese carps, a few diseases affecting theIndian and Chinese carps, a few diseases affecting the
eels and catfishes are de- scribed here.eels and catfishes are de- scribed here.
 It must be clear to person normally cannot identify allIt must be clear to person normally cannot identify all
the diseases of human beings and animals howeverthe diseases of human beings and animals however
much he tries to educate himself on those diseases somuch he tries to educate himself on those diseases so
also a fish farmer will be seldom able to identifyalso a fish farmer will be seldom able to identify
correctly each disease.correctly each disease.
 This booklet never intends to make anyone a specialistThis booklet never intends to make anyone a specialist
in fish diseases, but it is meant to introduce a commonin fish diseases, but it is meant to introduce a common
man into the whole world of fish diseases:man into the whole world of fish diseases:

 In the first two decades of post-independence, lot of interest was paid toIn the first two decades of post-independence, lot of interest was paid to InlandInland
fisheries and considerable amount of attention was paid to diseases infisheries and considerable amount of attention was paid to diseases in
cultivable fishes in various states. Fishes suffer from a wide variety ofcultivable fishes in various states. Fishes suffer from a wide variety of
diseases of infectious and non- infectious.diseases of infectious and non- infectious.
 Etiology in their natural environment. Number of literatures are available onEtiology in their natural environment. Number of literatures are available on
fish mortalities due to bacteria, parasites, fungus, nutritional deficiencies,fish mortalities due to bacteria, parasites, fungus, nutritional deficiencies,
metabolic disorders and faulty environmental conditions like oxygenmetabolic disorders and faulty environmental conditions like oxygen
deficiency, high or very low water temperature, chemical pollutants, overdeficiency, high or very low water temperature, chemical pollutants, over
crowding, mal-nutrition, algal blooms etc.crowding, mal-nutrition, algal blooms etc.
 In India, traditional aquacullure has in recent years turned into a scienceIn India, traditional aquacullure has in recent years turned into a science
based economic and commercial activity involving heavy inputs, andbased economic and commercial activity involving heavy inputs, and
therefore diseases of all kinds are now known to occur on an increasinglytherefore diseases of all kinds are now known to occur on an increasingly
larger scale.larger scale.
 However, fish mortality is not the only criterion to evaluate the effect of fishHowever, fish mortality is not the only criterion to evaluate the effect of fish
disease. Even the morbidity, which leads to weight losses and poor growth indisease. Even the morbidity, which leads to weight losses and poor growth in
surviving fish, contributes substantial losses to the farmers.surviving fish, contributes substantial losses to the farmers.
 Since last decade there is an increased realisation of the necessity to avoidSince last decade there is an increased realisation of the necessity to avoid
infectious agents to maintain healthy stocks to enhance production.infectious agents to maintain healthy stocks to enhance production.

Diseases of FishDiseases of Fish
 As already mentioned, diseases of fishes areAs already mentioned, diseases of fishes are
caused by various types of micro-organisms likecaused by various types of micro-organisms like
virus, bacteria, fungi, protozoa, etc. Hence, thevirus, bacteria, fungi, protozoa, etc. Hence, the
best way to study them is to study under thebest way to study them is to study under the
classification of causal organisms.classification of causal organisms.

A. Viral diseasesA. Viral diseases
 Virus is considered to be the lowest form of life and theVirus is considered to be the lowest form of life and the
link between the living and non-living. Some of thelink between the living and non-living. Some of the
important viral diseases of fish are briefly describedimportant viral diseases of fish are briefly described
here.here.
 Spring viremia of carp (SVC)Spring viremia of carp (SVC)
 Swim bladder inflammation (SBI)Swim bladder inflammation (SBI)
 Viral renal disease of eelsViral renal disease of eels
 Channel catfish viral diseaseChannel catfish viral disease
 . Pox disease of carps. Pox disease of carps
 Lymphocystis diseaseLymphocystis disease

Spring viremia of carp (SVC)Spring viremia of carp (SVC)
 Spring viremia of carp is also known as infectiousSpring viremia of carp is also known as infectious
dropsy of carp (IDC). This is caused by a virusdropsy of carp (IDC). This is caused by a virus
belonging to the Rhabdovirus group with ribonucleicbelonging to the Rhabdovirus group with ribonucleic
acid (RNA) structure and is calledacid (RNA) structure and is called Rhabdovirus caprioRhabdovirus caprio..
 It occurs in the spring when the water temperature isIt occurs in the spring when the water temperature is
raising (13 to 200 C) but it occurs most commonlyraising (13 to 200 C) but it occurs most commonly
when the temperature of the water is 170 centi- grade.when the temperature of the water is 170 centi- grade.
It is noticed that the outbreak ceases when theIt is noticed that the outbreak ceases when the
temperature exceeds 200 centigrade.temperature exceeds 200 centigrade.
 This disease usually occur in fish which are to one yearThis disease usually occur in fish which are to one year
old. It spreads fast and the mortality ranges between 80old. It spreads fast and the mortality ranges between 80
to 90 % in, 2 to 3 weeks time.to 90 % in, 2 to 3 weeks time.

 This disease is common among the carp in Europe andThis disease is common among the carp in Europe and
fortunately, it is not yet reported in our country. Because thefortunately, it is not yet reported in our country. Because the
virus cannot survive in temperatures above 20oC and ourvirus cannot survive in temperatures above 20oC and our
country mostly falls within the tropical and subtropical climates.country mostly falls within the tropical and subtropical climates.
 The affected fish show darkening of their body, and then tend toThe affected fish show darkening of their body, and then tend to
assemble at the water inlet. They exhibit sluggish breathing andassemble at the water inlet. They exhibit sluggish breathing and
finally tilt to one side. In the advanced stage of disease,finally tilt to one side. In the advanced stage of disease,
symptoms like abdominal distension, protrusion of the eyes,symptoms like abdominal distension, protrusion of the eyes,
reddening and swelling of the anus, anaemia and haemorrhagicreddening and swelling of the anus, anaemia and haemorrhagic
spots in the gills are seen.spots in the gills are seen.
 Various internal organs like intestine, spleen, kidney, etc, showVarious internal organs like intestine, spleen, kidney, etc, show
swelling and degradation.swelling and degradation.
 Scientists are of opinion that IDC is often mixed with bacterialScientists are of opinion that IDC is often mixed with bacterial
disorders. However use of antibiotics like chloramphenicol,disorders. However use of antibiotics like chloramphenicol,
streptomycin and oxytetracycline in the fish breeding ponds isstreptomycin and oxytetracycline in the fish breeding ponds is
found to be effective. The antibiotics are better, if given throughfound to be effective. The antibiotics are better, if given through
the artificial feed or through a bath or through injection.the artificial feed or through a bath or through injection.

Swim bladder inflammation (SBI)Swim bladder inflammation (SBI)
 It is caused by SBI virus belonging to the RhabdovirusIt is caused by SBI virus belonging to the Rhabdovirus
group with Deoxy ribo Nucleic Acid (DNA)group with Deoxy ribo Nucleic Acid (DNA)
chromosome structure. This is also a common diseasechromosome structure. This is also a common disease
in the Europe. Usually, young fishes up to two monthsin the Europe. Usually, young fishes up to two months
are infected more and the mortality could reach 100 perare infected more and the mortality could reach 100 per
cent. In the grown up fishes the incidence of thiscent. In the grown up fishes the incidence of this
sickness is rare.sickness is rare.
 Unlike the SVC/ IDC this disease occur at mediumUnlike the SVC/ IDC this disease occur at medium
temperatures. The suitable temperature range for thetemperatures. The suitable temperature range for the
replication SBI virus is found to be between 15 –28o Creplication SBI virus is found to be between 15 –28o C
and no growth takes-place above 33°C and below 5°and no growth takes-place above 33°C and below 5°
Centigrade.Centigrade.

 In the initial stages the inflammation occurs in the wall tissue of the swimIn the initial stages the inflammation occurs in the wall tissue of the swim
bladder, especially at the bottom of the swim bladder walls.bladder, especially at the bottom of the swim bladder walls.
 Gradually, bleeding spots appear and brown or black spots appear leading toGradually, bleeding spots appear and brown or black spots appear leading to
necrosis and the swim ' bladder is destroyed. By this time the infection wouldnecrosis and the swim ' bladder is destroyed. By this time the infection would
have extended to the other internal organs also.have extended to the other internal organs also.
 Administration of antibiotics either by injection or orally through feed isAdministration of antibiotics either by injection or orally through feed is
found to be effective to control this disease.found to be effective to control this disease.
 A dose of 40 mg of chloramphenicol per kilogram weight of the fish either asA dose of 40 mg of chloramphenicol per kilogram weight of the fish either as
abdominal injection or orally through feed is found to be effective.abdominal injection or orally through feed is found to be effective.
 In the case of yearlings 3 -4 administrations lasting for 10 days, and at 5-8 dayIn the case of yearlings 3 -4 administrations lasting for 10 days, and at 5-8 day
intervals 20 -30 mg of methylene blue per individual is reported to be useful.intervals 20 -30 mg of methylene blue per individual is reported to be useful.

Viral renal disease of eelsViral renal disease of eels
 The virus is identified as EV-E virus but to whichThe virus is identified as EV-E virus but to which
group it belongs is not yet confirmed. This disease isgroup it belongs is not yet confirmed. This disease is
particularly affecting the eels. It causes inflammationparticularly affecting the eels. It causes inflammation
mainly on the gills and kidneys and hence is called "gillmainly on the gills and kidneys and hence is called "gill
kidney in11ammation". Eventually the inflammationkidney in11ammation". Eventually the inflammation
leads to necrosis and degeneration of these organs andleads to necrosis and degeneration of these organs and
death of the eels.death of the eels.
 Fortunately, so far this disease is not yet reported in ourFortunately, so far this disease is not yet reported in our
country. Providing antibiotics through the feed ascountry. Providing antibiotics through the feed as
mentioned in the previous diseases described ismentioned in the previous diseases described is
probably the best way to control this disease.probably the best way to control this disease.

Channel catfish viral diseaseChannel catfish viral disease
 This disease is mainly affects the catfish and hence it is calledThis disease is mainly affects the catfish and hence it is called
catfish virus belonging to Herpes virus which has the DNAcatfish virus belonging to Herpes virus which has the DNA
structure of chromosomes. It usually affects the finger- lings ofstructure of chromosomes. It usually affects the finger- lings of
less than four months old during the period between June toless than four months old during the period between June to
September when the temperature exceeds 230 centigrade.September when the temperature exceeds 230 centigrade.
 The affected fish exhibit abnormal swimming patterns, circlingThe affected fish exhibit abnormal swimming patterns, circling
on their sides, exhibiting convulsions, sinking to the bottom ofon their sides, exhibiting convulsions, sinking to the bottom of
the pond and finally floating on the surface of the water and die.the pond and finally floating on the surface of the water and die.
They exhibit abnormal distension and protrusion of the anus inThey exhibit abnormal distension and protrusion of the anus in
the terminal stages. The disease is also characterized by thethe terminal stages. The disease is also characterized by the
protrusion of eyes and extreme fading of gills.protrusion of eyes and extreme fading of gills.
 Treatment with antibiotics as mentioned in the previous diseasesTreatment with antibiotics as mentioned in the previous diseases
is found to be effective besides the prophylactic measures likeis found to be effective besides the prophylactic measures like
cleanliness and proper maintenance of the pond.cleanliness and proper maintenance of the pond.

Pox disease of carpsPox disease of carps
 The virus causing the pox disease is identified as CarpThe virus causing the pox disease is identified as Carp
pox virus belonging to a group of virus called DNApox virus belonging to a group of virus called DNA
Herpes- virus. This is also called papilloma disease sinceHerpes- virus. This is also called papilloma disease since
it is characterized by the dense formation of papillomait is characterized by the dense formation of papilloma
in various sites on the trunk, head, and fins of carp fish.in various sites on the trunk, head, and fins of carp fish.
The papilloma are white or pink in colour.The papilloma are white or pink in colour.
 The disease does not seem to be fatal however, itThe disease does not seem to be fatal however, it
affects the growth and development of the fish. Theaffects the growth and development of the fish. The
virus is not yet isolated and hence its preventive andvirus is not yet isolated and hence its preventive and
curative measures are not finalized. However,curative measures are not finalized. However,
administration of antibiotics already mentioned throughadministration of antibiotics already mentioned through
feed is found to be effective.feed is found to be effective.

. Lymphocystis disease. Lymphocystis disease
 It is fairly certain that Lymphocystis is caused by virus. Though itIt is fairly certain that Lymphocystis is caused by virus. Though it
is commonly occurring in the wild fish the cultivated fishes areis commonly occurring in the wild fish the cultivated fishes are
also affected by it. However it is not reported to be really fatal.also affected by it. However it is not reported to be really fatal.
 Small blister-like swellings appear scatteringly or in clusters onSmall blister-like swellings appear scatteringly or in clusters on
the surface of the trunk, head, fins and other parts of the body.the surface of the trunk, head, fins and other parts of the body.
The disease occur in high temperatures (summer months) andThe disease occur in high temperatures (summer months) and
automatically disappear when the temperature becomes less.automatically disappear when the temperature becomes less.
 Antibiotics may be used at the beginning of the infection.Antibiotics may be used at the beginning of the infection.
However, proper sanitation and other prophylactic measures areHowever, proper sanitation and other prophylactic measures are
necessary to control the incidence of the disease.necessary to control the incidence of the disease.
 Proper feeding through the natural and artificial feeds is also aProper feeding through the natural and artificial feeds is also a
necessary element in the prevention and control of this disease.necessary element in the prevention and control of this disease.