Black Sea Journal of Agriculture
doi: 10.47115/bsagriculture.983345
Open Access Journal
e-ISSN: 2618 – 6578
Review
Volume 5 - Issue 1: 48-52 / January 2022
FUNGAL DISEASES IN FISH
Filiz ÖZCAN1*, Neval Berrin ARSERİM2
Dicle University, Veterinary Faculty, Department of Fisheries and Fisheries Diseases, 21280, Diyarbakır, Turkey
Dicle University, Veterinary Faculty, Department of Microbiology, 21280, Diyarbakır, Turkey
1
2
Abstract: Fungal diseases of fish have become increasingly important, over the past 20 years. The traditional ‘‘fungi’’ are comprised of
members from several different taxonomic kingdoms. An increasing number of other environmental fungi are being reported from
diseased fish, further testament to the opportunistic nature of many fungi. Active fungal agents living in waters cause infections in
juvenile and adult individuals in fish populations, leading to decay in eggs and larvae. Fungal infections that are generally observed as a
secondary infection in fish populations become established in lesions caused as a result of mechanical injury by bacterial, viral, and
parasitic primary agents, consequently causing a change in the prognosis of the disease. Fungi, however, can cause disease under a
variety of other circumstances. Some may be more aggressive and play a more primary role. Fungi can be external or internal, and
systemic. Fungi can cause problems during reproduction, for example, by infecting fertilized eggs in spawns. Certain species of fungi
can grow in poorly stored feeds and produce mycotoxins. Fungal diseases, in general, are very difficult to control or treat once they
have taken hold. Prevention is, as always, the best medicine. Increased knowledge of basic biology will help guide treatment and
control methods. This review study sought to provide insights into the fungal diseases of wild or farmed fish introduced onto the
market.
Keywords: Fish, Fungi, Mycotic diseases
*Corresponding author: Dicle University, Veterinary Faculty, Department of Fisheries and Fisheries Diseases, 21280, Diyarbakır, Turkey
E mail: filiz.ozcan@dicle.edu.tr (F. ÖZCAN)
Filiz ÖZCAN
https://orcid.org/0000-0003-4767-9893
Received: August 16, 2021
Neval Berrin ARSERİM
Accepted: October 07, 2021
Published: January 01, 2022
https://orcid.org/0000-0002-7097-0091
Cite as: Özcan F, Arserim NB. 2022. Fungal diseases in fish. BSJ Agri, 5(1): 48-52.
1. Introduction
The ever-increasing world population has led to
increasing demand for protein, a condition that has
generated a growing interest in fish meat as a source of
rich protein. Fish farming is of great importance in
meeting a particular part of the need for fish meat. Data
published by FAO in 2020 indicate that the total
aquaculture production in the world has reached an
amount of approximately 178.5 million tonnes (FAO,
2020). The aquaculture production in Turkey, on the
other hand, amounts to 314.537 tonnes, with the
rainbow trout (Oncorhynchus mykiss) produced in inland
waters having the greatest quota in the production with
103.192 tonnes (TUİK, 2018). The total global production
of this species, on the other hand, amounts to 848
thousand tonnes. Rainbow trout production represents
circa 50% of the total fish production in Turkey (TUİK,
2019). The problems producers experience in
aquaculture production also lead to economic losses,
inflicting financial and moral damages on enterprises
(Yilmaz et al., 2011). It is a fact that diseases account for
most of the burden arising from monetary losses. Fungal
infections represent an essential part of fish diseases.
There is a considerable amount of literature on fungal
diseases in fish (Silphaduang et al., 2000; Rand et al.,
2000; Blaylock et al., 2001). It is of prime importance to
define and isolate the related agent to understand the
BSJ Agri / Filiz ÖZCAN and Neval Berrin ARSERİM
biological characteristics of fungal disease and diagnose
and treat it. The present review study sought to provide
insights into the fungal infections that afflict fish
populations.
2. Saprolegniasis
Saprolegniasis is the most frequently seen and
economically most significant disease caused by fungi. It
is also called winter fungus or winter kill syndrome
(Durborow et al. 2003). It is known that Saprolegnia has
approximately 14 genera and between 126 and 146
species, among which S. parasitica and S. invaderis are
the most common. It is the fungal disease most
frequently seen in freshwater and marine fish
populations (Yarsan, 2020). The Saprolegnia genus
members belonging to the Oomycete family cause a
disease called Saprolegniasis (Beakers et al., 1994;
Roberts, 1989). Most of the fungal infections that affect
fish are categorized as opportunistic invasive infections.
Adverse environmental conditions and stress lead to
suppression in the immune system. With excessive
mucus secretion, fungi begin to settle secondary to
bacterial and viral infections (Khoo, 2000). However, it
has been observed that some Saprolegnia species cause
fatal and primary diseases, especially in catfish.
Saprolegnia is ubiquitous in freshwater ecosystems. It
damages the epidermal tissues in fish and can spread to
This work is licensed under Creative Commons Attribution 4.0 International License
48
Black Sea Journal of Agriculture
the whole body, starting from the head and fins (Kutama
et al., 2013). Among the Saprolegnia species, S. parasitica
is a highly virulent species that cause extensive fish kills
and decay in eggs in salmon and trout farming (Jiang et
al., 2013). The disease's lesions manifest themselves in
the skin, gills, and especially in fish eggs in the form of a
cotton wool puff (Figure 1).
Fungi colonies consist of heavily branched filaments
called hyphae. Many hyphae form a fungus network
called mycelium (Yarsan, 2020). As the mycelium is the
vegetative part through which a fungus absorbs
nutrients, lesions in diseases can be of different colours
due to mycelia. Since mycelia feed on algae, they may
appear red and brown. First attacking the gill,
Saprolegnia moves on to infect the eye, brain, liver,
spleen, kidney, and swim bladder (Neish and Hughes
1980; Ferguson, 1989). Research has reported limited
success in treatment. Water quality, particularly water
temperature, is vital in dealing with the disease.
Environmental conditions should be improved, and egg
and pond disinfection should be performed.
Research reports that 87 fish species have so far been
affected by EUS (Kamilya and Baruah 2014). It is seen
more frequently in juvenile individuals than in adult fish
(Pagrut et al., 2017). Normally, the skin of fish has the
function of a defense system. But changes in
environmental factors that lead to lower pH and lower
oxygen content influence the defense system, leading to
the suppression of the immune system and consequently
to EUS epidemic in some cases (Kiryu et al., 2005).
Infections begin with the attachment of motile zoospores
to damaged areas. The hyphae, composed of zoospores,
deeply invade the lower tissues, causing excessive
ulceration and destruction in the tissue. The occurrence
of skin lesions varies depending on the fish species.
Mildly infected fish show only minor inflammation
without external lesions, but also petechial
haemorrhages in the body, mouth, as well as on the anal
fin and exophthalmos (İberahim et al., 2018). Ulcers
appear as white areas on the fish’s skin, which turn
entirely red with a reddish center and later cause
external factors. As the disease progresses, the eyes
protrude, the body decays, and in some cases the head is
eroded, resulting in the death of the fish depending on
the severity of the disease (Podeti and Benarjee 2017).
Although Aphanomyces invidans is the causal agent of
EUS, it can be isolated from fish infected with other
pathogenic viruses (mostly rhabdovirus), bacteria
(mainly Aeromonas hydrophila), or parasitic protozoans
with A. invadans (Huchzermeyer et al., 2012). These
infections cause stress in fish and can render them more
vulnerable to diseases. Malachite green is important in
treatment. It has, however, been prohibited worldwide as
it affects the environment and people working in the
enterprises in the sector. It is a disease difficult to treat; it
is, therefore, important to provide proper nutrition, ideal
stock ratio, and optimum water quality conditions
(İberahim et al., 2018).
Figure 1. Saprolegnia infections (Chesser, 2020).
3. Aphanomycosis (Epizootic Ulcerative
Syndrome)
Aphanomyces was first described by Bary in 1860 and
was included in the Leptoleniaceae family by Dick et al.
(1999) due to its morphological similarity to this family.
It includes about 45 zoopathogenic species found in
freshwaters and marine environments. The most
reported species are Aphanomyces invidans infecting fish
populations, and Aphanomyces astaci that are mainly
observed in arthropods. Aphanomyces invidans that is the
causal agent of Epizootic Ulcerative Syndrome (EUS)
causes mortality up to 100% in aquaculture (Figure 2). It
was first defined in Japan in 1971 (İberahim et al., 2018).
BSJ Agri / Filiz ÖZCAN and Neval Berrin ARSERİM
Figure 2. Ulcers on the lateral and fins due to EUS effect
(FAO, 2020; Huchzermeyer et al., 2012).
49
Black Sea Journal of Agriculture
4. Branchiomycosis (Gill Rot Disease)
Branchiomycosis is a much-feared fungal disease in fish
farms (mainly in carp farms) and is in the gill epithelium
and capillaries. This fungal disease, called gill rot,
generally causes high fish mortality, being acute in some
freshwater fish (Judy, 2010) It is usually seen in regions
with a hot climate (Ramaiah, 2006) Water temperature,
the amount of organic matter, and the high amount of
ammonia in the ponds fertilized with organic fertilizers
are the critical factors that fundamentally influence the
prognosis of the disease. Branchiomycosis is an acute
infection of the gills that can cause high mortality and
respiratory distress in Koi, eel, perch, and many
freshwater fish species. It is also called gangrenous
bronchitis. Cases have been reported in Europe, Taiwan,
and the USA. There are two agents isolated from this
disease (Noga, 2010).). While Branchiomyces sanguinis
and B. demigrans. B. sanguinis affect carp and tench
populations, B. demigrans mainly affects the populations
of pike, sea bass, and tench (Riad et al., 2015). The two
species have significant distinguishing features. B.
demigrans can multiply and spread outside the blood
vessel. It differs from B. sanguinis in that it has thicker
hypha walls and larger spores (Patel et al., 2018). Both
species are seen in fish in environments with low
dissolved oxygen and low pH (5.8-6.5) as well as in those
being under stress. Respiratory distress, loss of appetite,
weakening of movements, and lack of feed are observed
in infected fish. This disease, which manifests itself with
the necrosis of the gills in fish, causes respiratory distress
in the infected gills and is characterized by high mortality
due to fungal spores falling from necrosed gills (Figure 3)
(Adeshina et al., 2019). There is no cure for
branchiomycosis. Dead fish must be removed from ponds
and disposed of. Surviving fish are carriers of the
infection and should never meet with intact fish in any
way (Lio-Po and Lim 2002, Chalmers, 2003). Poor
environmental conditions do constitute a vital stress
factor for Branchiomycosis induction in infected fish.
Water quality parameters, predominantly temperature,
dissolved oxygen, and nitrogenous wastes, should be
kept at optimum values (Ali, 2005).
skin and tail region (Figure 4) (Govind et al., 2012). An
emery-paper-like appearance is particularly noticeable
on the fungi granulomas due to epithelial loss. Besides, it
affects the central nervous system, particularly in
salmonids, as a result of which neurological symptoms
such as swimming and balance disorder, swaying
movement are observed in fish (Hodneland et al., 1997).
The disease mainly attacks the liver. Apart from the liver,
the spleen, heart, kidney, gonads, brain, gills, muscles,
and nerve tissues behind the eyes are severely affected.
Spinal curvature has been observed in some fish (Govind
et al., 2012). The prognosis of the disease varies
according to the host involved and environmental
conditions (Kocan et al., 2009). There is no cure for the
disease. The contaminated feed should be avoided, and
factors causing stress should be eliminated (Choudhury
et al., 2014).
Figure 3. Pale, necrotized, and obstructed gills caused by
branchiomycosis (Khalid Subhi, 2011; Riad et al., 2015).
5. Ichtyosporidis (Swinging Diseases)
It is a chronic, systemic granulomatosis internal fungal
disease, which is endemic in both freshwater and marine
fish and is mainly seen in trout. The causal agent of the
disease is Ichthyophonus hoferi (Choudhury et al., 2014).
The disease was first described by Hofer in 1893 in
brown trout. Cases have been reported in more than
eighty fish species (Zadeh et al., 2014). The agent
develops in low water temperatures. The optimum water
temperature likely to favor the development of the
disease has been reported as 10 °C. The spread of the
disease occurs through dead and infected fish, fungal
cysts in the feces and cysts free in the water, and foods
containing fungi. Internal nodules arise primarily in the
BSJ Agri / Filiz ÖZCAN and Neval Berrin ARSERİM
Figure 4. Granulomas formed in the liver and intestine as
a result of Ichtyosporidis (Huntsberger et al., 2017).
6. Conclusion
Fungal infections represent an essential part of fish
diseases. There is a considerable amount of literature on
fungal diseases in fish controlling fungal diseases is
necessary to ensure continued growth in the aquaculture
industry. It is important to continue studying the
underlying molecular processes of fungal – host fish
interactions.
50
Black Sea Journal of Agriculture
Author Contributions
All authors had equal contribution and all authors
reviewed and approved the manuscript.
Conflict of Interest
The authors declare that there is no conflict of interest.
References
Adeshina I, Amoka PO, Tiamiyu LO, Abubakar MI, Adesanmi O.
2019. Natural formation and pathological effects of
branchiomyces species in farm-grown African catfish (Clarias
gariepinus) in Ilorin metropolis. Harran Üni Vet Fak Derg,
28(2): 186-190.
Ali EH. 2005. Morphological and biochemical alternations of
Oomycetes fish pathogen Saprolegnia parasitica as affected
by salinity, ascorbic acid and their synergistic action.
Mycopathologia, 159(2): 231-43.
Beakers GW, Wood SE, Burr AW. 1994. Features which
characterize Saprolegniaisolates from salmonid fish lesions a
review. In Salmo saprolegniasis, Edited by G.J. Mueller.U.S.
Depart of Energy, Bonnevilla Power Administration, Portland,
Oregon, US, pp: 66.
Blaylock RB, Overstreet RM, Klich MA. 2001. Mycoses in red
snapper (Lutjanus campechanus) caused by two deutero
mycete fungi (Penicillium corylophilum and Cladosporium
sphaerospermum). Hydrobiologia, 460: 221-228.
Chalmers GA. 2003. Infectious diseases of silver carp,
Hypophthalmichthys molitrix (Valenciennes, 1844). Goldon A
Chalmers, DVM Lethbridge, Alberta, US, pp: 56.
Chesser B. 2020. Saprolegniasis, aquaculture, fisheries & pond
management.
URL:
https://fisheries.tamu.edu/2020/01/24/saprolegniasis/
(access date: April 11, 2021).
Choudhury TG, Singh SK, Parhi J, Barman D, Das BS. 2014.
Common fungal diseases of Fish: A review. Environ Ecol,
32(2): 450-456.
Dick MW, Vick MC, Gibbings JG, Hedderson TA, Lopez-Lastra
C.C. 1999. 18Sr DNA for species of Leptolegnia and other
Peronosporomycetes: justification for the subclasstaxa
Saprolegniomycetidae and Peronosporomycetidae and
division of the Saprolegniaceae sensulato into the
Leptolegniaceae and Saprolegniaceae. Mycol Res, 103: 1119–
1125.
Durborow RM, Wise JD, Terhune JS. 2003. Saprolegniasis
(winter fungus) and branchiomycosis of commercially
cultured channel catfish, 2003. Southern Regional
Aquaculture Publication No, 4700, Stoneville, US, pp: 4.
FAO. 2020. Food and Agriculture Organisation Global Fisheries
and Aquaculture Production Statistics. Fish Stat J Rome, Italy.
URL: http://www.fao.org (access date: April 20, 2021).
Ferguson HW. 1989. Systemic pathology of fish. Ames, IA, Iowa
University press 1, Iowa, US, pp: 263.
Govind P, Sharma M, Shrivastav AB. 2012. Overviews of the
treatment and control of common fish diseases. Int Res J
Pharm, 3(7): 123-127.
Hodneland K, Karlsbalck E, Skagen DW. 1997. Ichthyophonus
hoferi in Norwegian spring spawning herring (Clupea
harengus L.). IFM Report, 3: 28.
Huchzermeyer KDA, Van der Waal. 2012. Epizootic ulcerative
syndrome: Exotic fish disease threatens Africa’s aquatic
ecosystems. J South African Vet Assoc, 83: 1-6.
Huntsberger CJ, Hamlinb JR, Smolowitza RJ, Smolowitzb RM.
2017. Prevalence and description of Ichthyophonus sp. in
yellow tail flounder (Limanda ferruginea) from a seasonal
BSJ Agri / Filiz ÖZCAN and Neval Berrin ARSERİM
survey on Georges Bank. Fisheries Res, 194: 60-67.
İberahim NA, Trusch F, Pietervan W. 2018. Aphanomyces
invidans the causal agent of Epizootic Ulcerative Syndrome, is
a global threat to wild and farmed fish. Fungal Biology Rev,
32(3):118-130.
Jiang RH, de Bruijn I, Haas BJ, Belmonte R, Löbach L, Christie J,
Van den Ackerveken G, Bottin A, Bulone V, Díaz Moreno SM.
2013. Distinctive expansion of potential virulencegenes in the
genome of the oomycete fish pathogen Saprolegnia
parasitica. PLoS Genetics, 9: e1003272.
Judy S. 2010. Comparative pathology of fishes. Leger Sea World,
San Diego, US, October 20, 2010.
Kamilya D, Baruah A. 2014. Epizootic ulcerative syndrome
(EUS) in fish: History and current status of understanding.
Rev Fish Biol Fisher, 24: 369-380.
Khalid Subhi I. 2011. Isolation and pathological study of
Branchiomycosis from the commercial pond of common carp
(Cyprinuscarpio) fish, in Governorate of Duhok / Iraq. The
Iraqi J Vet Medicine, 35(1): 1-9.
Khoo L. 2000. Fungal diseases in fish. Avian and Exotic Pet
Med, 9(2): 102-111.
Kiryu Y, Blazer VS, Vogelbein WK, Kator H, Shields JD. 2005.
Factors influencing the sporulation and cystformation of
Aphanomyces invadans, etiological agent of ulcerative
mycosis in Atlantic menhaden, Brevoortiatyrannus.
Mycologia, 97: 569-575.
Kocan R, Hershberger P, Sanders G, Winton F. 2009. Effects of
temperature on disease progression and swimming stamina
in Ichthyophonus-infected rainbow trout, Oncorhynchus
mykiss (Walbaum). J Fish Diseas, 32: 835-843.
Kutama AS, Umar S, Fagwalawa LD, Ahmed MK, Bilkisu AI.
2013. Detection of fish saprolegniasis in thomas dam and
challawa commercial fish pond. Global Advanced Research J.
Agri Sci, 2(12): 315-321.
Lio-Po GD, Lim LHS. 2002. Infectious diseases of warm water
fish in fresh water. In: Diseases and Disorders of Finfish in
Cage Culture (Ed. by P. T. K. Woo, D. W. Bruno& L. H. S. Lim).
CABI Publishing, Wallingford, UK, pp. 231-281.
Neish GA, Hughes GC. 1980. Fungal diseases of fishes. THF
publication, Neptune, US, pp: 346.
Noga EJ. 2010. Fish disease: Diagnosis and treatment”; 2nd
Edition. Wiley-Blackwell, New York, US, pp: 536.
Pagrut NK, Ganguly S, Jaiswal V, Singh C. 2017. An overview on
epizootic ulcerative syndrome of fishes in India: A
comprehensive report. J Entomol Zool Stud, 5: 1941-1943.
Patel AS, Patel SJ, Bariya AR, Pata BA, Ghodasara SN. 2018.
Fungal diseases of fish: A review. J Vet Sci Res, 3(3): 000-164.
Podet KR, Benarjee G. 2017. Haematological changes in South
Indian fresh water murrel, Channa punctatus have both EUS
and A. hydrophila infection. J Parasitic Diseas, 41: 329-335.
Ramaiah N. 2006. A review on fungal diseases of algae, marine
fishes, shrimps and corals. Indian J Marine Sci, 35: 380-387.
Rand TG, Bunkley-Williams S, Williams EH. 2000. A
hyphomycetes mantar, Paecilomyceslilacinus, associated
with wasting disease in two species of tilapia from Puerto
Rico. J Aquatic Anim Health, 2: 149-156.
Riad H, Khalil Talaat T, Saad Talal A, AboSelema M, Hany MR.
Abdel-Latif A. 2015. Branchiomyces demigrans infection in
farm‐reared common carp (cyprinus carpio l.) and nile tilapia
(oreochromis niloticus) at different localities in egypt, with
special emphasis to the role of environmental stress factors.
Int J Innov Stud Aquatic Biol Fisher, 1(1): 15-23.
Roberts RJ. 1989. Fish pathology, Second edition. Bailiere
Tindall publishers, London, UK, pp: 467.
Silphaduang U, Hatai K, Wada S, Noga S. 2000. Cladosporium
51
Black Sea Journal of Agriculture
infection in tomato clown fish. J Zoo Wild Life Med, 31: 259261.
TÜİK. 2018. The Statistical Agency of Turkey, aquaculture
statistics 2018. URL: http://www.tuik.gov.tr (access date:
April 01, 2021).
TÜİK. 2019. Statistical Agency of Turkey, aquaculture efficiency
report. URL: http://www.tuik.gov.tr (access date: April 01,
2021).
BSJ Agri / Filiz ÖZCAN and Neval Berrin ARSERİM
Yarsan E. 2020. Balık hekimliği. Güneş Tıp Kitap Evi, Ankara,
Turkey, pp: 552.
Yilmaz E, Yilmaz A, Bilgin B. 2011. Alabalık kuluçkahanelerinde
görülen önemli hastalıklar ve tedavi yöntemleri, Türk Bil
Derlemeler Derg, (2): 37-39.
Zadeh MJ, Peyghan R, Manavi SE. 2014. The detection of
ichthyophonus hoferi in naturally infected fresh water
ornamental fishes. J Aquacul Res Develop, 5: 289.
52