Microorganisms: Parasite Diversity in A Freshwater Ecosystem
Microorganisms: Parasite Diversity in A Freshwater Ecosystem
Microorganisms: Parasite Diversity in A Freshwater Ecosystem
Article
Parasite Diversity in a Freshwater Ecosystem
Amana Shafiq 1, *, Farzana Abbas 1, *, Muhammad Hafeez-ur-Rehman 1 , Bushra Nisar Khan 2 , Ayesha Aihetasham 2 ,
Iffat Amin 3 , Hmidullah 4 , Ramzi A. Mothana 5 , Mohammed S. Alharbi 5 , Imran Khan 6 , Atif Ali Khan Khalil 7 ,
Bashir Ahmad 8 , Nimra Mubeen 1 and Muneeba Akram 1
Abstract: Parasites are a significant component of biodiversity. They negatively affect fish appear-
ance, growth, and reproduction. In this study, the prevalence of infection, diversity, and mean
intensity of parasites were examined in 9 freshwater fish species (45 samples per fish species).
Ecto-parasites were examined on the skin, gills, and fins with a hand lens. Wet mounts were
prepared using mucosal scrapings from all the external and internal organs of the sampled fish.
Microscopy, muscle compression, and the pepsin-HCL artificial digestion technique were also per-
Citation: Shafiq, A.; Abbas, F.; formed. In this study, 26 species of parasites were identified including three taxa belonging to
Hafeez-ur-Rehman, M.; Khan, B.N.; 9 species of protozoan parasites, 11 treamtodes, and 6 monogenean parasites. The identified pro-
Aihetasham, A.; Amin, I.; Hmidullah; tozoan parasites were Entamoeba histolitica, Chilodonella sp., Coccidia sp., Costia sp., Cryptobia sp.,
Mothana, R.A.; Alharbi, M.S.; Khan, Ichthyopthiris-multifilis, Microsporidia, Piscinoodinium sp., and Ichthyobodo necator. The identified trema-
I.; et al. Parasite Diversity in a tode parasites were Fasciola gigantica, Echinostoma revolutum, Fasciola hepatica, Haplorchis pumilio,
Freshwater Ecosystem.
Brachylaima cribbi, Echinostoma cinetorchis, Neascus sp., Deropegus sp., Trematode Soldier, Centrocestus
Microorganisms 2023, 11, 1940.
formosanus, and Clinostomum marginatum. The identified monogenean parasites were Dactylogyrus
https://doi.org/10.3390/
limipopoensis, Dactylogyrus anchoratus, Dactylogyrus myersi, Dactylogyrus vastator, Gyrodactylus salaris,
microorganisms11081940
and Ancyrocephalus. The diversity of parasites was maximum at the Okara site. The host’s organs
Academic Editors: Jarl Bøgwald, that were targeted for parasitic infection included the intestine, liver, gills, fins, skin, and kidneys.
Luca Villa, Aleksandra Uzelac and
The majority of the parasites were identified in Labeo rohita followed by Hypophthalmichthys molitrix,
Ivana Klun
Ctenopharyngodon idella, Oreochromis niloticus, Cyprinus carpio, and Wallagu attu. Two species appeared
Received: 3 July 2023 to be resistant species because none of the parasites were observed in Notopterus notopterus or Sperata
Revised: 11 July 2023 seenghala. This study also concluded that the prevalence of parasites increased with increasing length,
Accepted: 21 July 2023 size, and age of fish.
Published: 29 July 2023
Keywords: protozoa; monogeneans; trematodes; prevalence of infection; mean density; diversity
to the significance of fish health. The host’s tissues or digested gut contents are the pri-
mary sources of nutrition for fish parasites, and upon favorable conditions, the parasites
reproduce rapidly [2].
The rate of parasitic infection in fish is high among vertebrates, which is related to
the aquatic environment in terms of dispersion, life cycle, and reproduction [3]. Parasites
are ubiquitous in Asian countries and thus reduce aquaculture productivity, which is an
important source of employment in many countries [4]. Parasites enhance their trans-
mission in fish by altering the host’s eating, mating, and social behavior and migration
patterns [5]. They also influence the neurological system of their host, interfere with the
secretary functions of the alimentary canal and metabolism, and damage fish skin and
gills by causing sores, ulceration, and tissue deterioration [6]. Parasites can influence the
structure of fish communities [7]. Adult parasites are more dangerous, depending on
the parasite load and size of the host, as well as the form of attachment [8]. In certain
circumstances, parasites do not kill fish, but they have a negative impact on the population
and individual fish. Protozoans, trematodes, and monogeneans are the most common
parasites of fish species [9].
Protozoan parasites are of great importance as they vary in size and shape. Protozoan
parasites have diversified classification [10]. Among the protozoan parasites, Ichthyobodo
necator (Henneguy, 1883), Ichthyophthirius multifiliis (Fouquet, 1876), Trichodina sp. (Ehren-
berg 1831), and Trichophyra and Hexamita (J. R. Uzmann, J.W. Jesse 1963) are some of the
most significant pathogens that cause diseases in aquaculture [11]. They raise farm in-
puts due to increased handling costs and yield insufficient growth rates due to disease
outbreaks [12]. Protozoan parasites cause severe diseases in freshwater fishes all over the
world including ichtyobodiasis, coccidiosis, ichtyopthiariasis, and trichodiniasis [13]. The
mortality rate of infected fish can reach almost 100% [14]. Parasitic diseases have gained
much attention in research as fish consumption has increased in the last decade.
Fishbone trematodes cause serious infections in humans if they are consumed im-
properly [15]. Fish-borne trematodes affect the health of more than 40 million people in
the world [4]. In 2005, 56.2 million people were infected with foodborne trematodiasis,
including 7158 deaths [16]. Many farmers experience economic losses due to trematode
parasites [17]. Trematodes belong to the phylum Platyhelminthes. Adult trematodes
are obligatory parasites of many vertebrates. Trematodes complete their life cycle in
four hosts [18,19]. Trematodes of the family Heterophyidae are intestinal trematodes. Their
final hosts are mammals and birds. There are 22 species in the Heterophyidae family that
cause infection in humans worldwide. Some previous studies reported that Haplorchis
pumilio and Centrocestus formosanus were zoonotic species found in Sutchi catfish, but
some unidentified species were also found, suggesting that there is a need for further
investigation [20]. There is a need to record the distribution of parasites in relation to
host size, season, and farm management [21]. The effects of the trematode metacercariae
on fish include delayed growth of young fish and decreased immunity of fish, due to
which secondary infections may also occur. Some other diseases include black spot disease,
malformations in fish, inflammation of the liver, necrotic tissue change, displacement of
organs, functional morbidity, and severe gill damage [22].
Monogeneans are a typically diverse group of ectoparasites of freshwater and marine
fishes [23]. Monogeneans worms and their communities in cultured fish affect ecosystem
health [24]. Monogeneans cause an increase in fish mortality due to various infections such
as respiratory problems, anemia, and osmoregulatory dysfunction, and they also cause
secondary microbial infection. Mongenean infestations in fish aquaculture bring about
large financial losses [25]. The monogenean life cycle was found to rapidly increase in an
artificial environment, which caused injurious infection in their hosts [26]. Depending on
the fish species, monogeneans attach to the gills, the surface of the skin, fins, and eyes and
typically fed on the blood, mucus, and epidermal cells of their host. Small- to medium-sized
monogenean parasites complete their life cycle in a single host [27]. Different species of
monogenean have been involved in the death of wild and cultured fish such as tilapia [28].
Microorganisms 2023, 11, x FOR PEER REVIEW 3 of 16
typically fed on the blood, mucus, and epidermal cells of their host. Small- to medium-
Microorganisms 2023, 11, 1940 3 of 16
sized monogenean parasites complete their life cycle in a single host [27]. Different species
of monogenean have been involved in the death of wild and cultured fish such as tilapia
[28]. Members of Dactylogyridea, Ancyrocephalidae, and Gyrodactylidae have been re-
Members
ported inof Dactylogyridea,
cultured Ancyrocephalidae,
and wild fish. and Gyrodactylidae
Transmission of these parasites mostly have been
depends onreported
host-
into-host
cultured and wildalthough
interactions, fish. Transmission of these
parasites may parasites
also occupy mostly
a new host depends onwith
by drifting host-to-host
water
interactions,
currents or although
depending parasites
on water may also occupy
quality, a new host
which directly by drifting
affects with water
their infection currents
processes
or[29].
depending
In pollutedonwater,
waterparasitic
quality, infections
which directly affects
commonly their infection
increase, processes
and they provide an [29].
indi- In
cation ofwater,
polluted water parasitic
quality [30].
infections commonly increase, and they provide an indication of
water Relatively
quality [30].little research has been conducted on freshwater fish parasites. The identi-
fication of parasites is important
Relatively little research has for determining
been conductedthe on specific etiology
freshwater of sicknesses.
fish parasites. TheOnce
identifi-
cation of parasites is important for determining the specific etiology of sicknesses.and
the diversity of fish parasites is established, identification of the disease-causing agent Once
their
the pathogenicity
diversity will be easily
of fish parasites accessible.identification
is established, After the identification of parasites, the
of the disease-causing riskand
agent
of infection
their can be determined
pathogenicity will be easily using the prevalence
accessible. of parasites
After the in fishofand
identification differentthe
parasites, water
risk of
bodies. The present study was therefore designed to identify parasites of
infection can be determined using the prevalence of parasites in fish and different waterfreshwater fishes
in River
bodies. Ravi,
The Pakistan
present study was therefore designed to identify parasites of freshwater fishes
in River Ravi, Pakistan
2. Materials and Methods
2.2.1.
Materials and Methods
Study Site
2.1. Study Site
Fish samples were collected from 3 different harvesting sites (River Ravi Down-
stream
FishHead Balloki
samples District
were Kasur,
collected fromLower Bari Doab
3 different Canal District
harvesting Kasur,Ravi
sites (River and River Ravi
Downstream
TehsilBalloki
Head Okara)District
in RiverKasur,
Ravi. Samples were
Lower Bari collected
Doab Canalduring theKasur,
District harvesting season
and River (2020–
Ravi Tehsil
2021). in River Ravi. Samples were collected during the harvesting season (2020–2021).
Okara)
Laboratory
Microorganisms 2023, 11, x FOR PEER of Fisheries and Aquaculture, University of Veterinary and Animal
REVIEW 4 of Sciences,
16
Ravi campus.
2.3.1822),
Examination of Protozoan
Hypophthalmichthys Parasites
molitrix (Valenciennes, 1844), Ctenopharyngodon idella (Valenci-
2.3.1. Study
ennes, of Cirrhinus
1844), External mrigala
Protozoan Parasites
(Hamilton, 1822), Cyprinus carpio (C. Linnaeus, 1758), Wal-
lagu attulength
The (Bloch and
and Schneider,
weight of1801),
all theNotopterus
fish werenotopterus
recorded.(Pallas,
For 1769), Sperata
the study ofseenghala
ectoparasites,
(Sykes, 1839), and Oreochromis niloticus (Linnaeus, 1758). The samples were
external organs of the fish such as skin, scales, fins, tails, etc., were examined examined
with a hand
physically
lens. Permanent to assess
and the
wetgeneral
mounts health
werestatus of theby
prepared fish. For further
scraping investigation, surface
the dorsolateral fish of
samples were kept in plastic bags within ice boxes after labeling and then transported
a fish with the dull side of a scalpel blade. Scrapings were obtained from near the base
immediately to the Laboratory of Fisheries and Aquaculture, University of Veterinary and
of all the fins [31]. To observe gill parasites, the operculum was removed from the fish.
Animal Sciences, Ravi campus.
In the case of a small fish, the entire gill arch was removed, transferred to a slide, and
examined under a microscope. In the case of a larger fish, the bony arch was also removed
and examined under a stereomicroscope. Furthermore, the gills were also dissected from
the branchial cavity and placed in a mixture of 1:4000 formalin solution for one hour.
The decanted sediments were placed in a Petri dish and analyzed for protozoan parasites
under a stereoscopic microscope at low and high magnifications [32]. Photographs of the
identified external protozoan parasites are shown in Figure 1a.
(Entamoeba Histolitica)
(Coccidia) (Chilodonella)
Figure 1. Cont.
Microorganisms
Microorganisms 2023,
2023, 11,
11, x1940
FOR PEER REVIEW 5 5ofof 16
16
(Fasciola
(Fasciola gigantica) (Echinostoma revolutum) hepatica)
Figure 1. Cont.
Microorganisms 2023, 11, 1940 6 of 16
Table 1. Cont.
stereomicroscope by compressing a longer section of the intestine between the glass slides.
Wet mounts were prepared using a scraping from the affected fish after fixing it in a 10%
buffered neutral formalin solution. These samples were then stained with hematoxylin
and counter-stained with eosin for examination under a microscope at both low and high
magnification [32]. Photographs of the identified internal protozoan parasites are shown in
Figure 1a.
Prevalence = no. of individual of a host infected with a particular parasite species ÷ no. of hosts examined × 100
Microorganisms 2023, 11, 1940 9 of 16
3. Results
During the harvesting season (2020–2021), nine species of freshwater fish were sam-
pled from the three study sites. In total, 405 freshwater fish from these nine fish species
(45 samples per fish species) were examined, including carp, catfish, and tilapia. The
weight of the fish that were examined during this study was between 100 g and 3000 g. The
results revealed that parasite prevalence was high in large-sized fish compared to small- or
medium-sized fish.
Table 1: In total, 9 species of protozoan parasites, 11 species of trematodes, and
six species of monogenean parasites were identified in different organs from seven fresh-
water fish species. Protozoan parasites were observed on the external and internal organs
of fish such as the intestine, liver, kidneys, skin, and fins. Trematodes were found only
in the intestine and gills. Monogeneans were found only on the external organs of fish,
i.e., the skin, gills, and fins. Two fish species, Sperata seenghala and Notopterus notopterus,
were identified as resistant species as none of the parasites was observed in either of these
fish species.
Table 2: In total, 573 parasites were identified in 405 fish consisting of 210 protozoan
parasites, 185 trematode parasites, and 178 monogenean parasites. The rate of parasite
infection was calculated by counting the total number of parasite species for each class at
a specific site. The chi-square (X2 ) statistic was used to analyze the relationship between
parasites and a specific site. The level of significance was set at p < 5% (Table 2). The
statistical analysis revealed that there was not any association between parasites and a
specific site. The existence of parasites was not site-specific.
Table 2. The rate of parasite infection at three different study sites in River Ravi.
Table 2. Cont.
Table 3 lists the infection rate of individual fish species for each protozoan parasite in-
cluding Chilodonella, Coccidia, Costia, Cryptobia, Entamoeba histolitica, Icthyophthirus multifillus,
Microsporidia, Piscinoodinium, and Ichthyobodo necator. The number of infected fish with a
certain number of protozoan parasites is also listed. The prevalence of infection, mean
intensity, and mean abundance were calculated using the formulas mentioned in Section 2.6.
Photographs of each protozoan parasite are shown with their names in Figure 1a.
Table 3. Infection rate of each fish species for each protozoan parasite.
Table 3. Cont.
Table 4 lists the infection rate of individual fish species for each trematode parasite
including Brachylaima cribbi, Centrocestus formosanus, Clinostomum marginatum, Deropegus sp.,
Echinostoma cinetorchis, Echinostoma revolutum, Fasciola hepatica, Fasciola gigantica, Haplorchis
pumilio, Neascus, and Trematode Soldier. The number of infected fish with a certain number
of trematode parasites is also listed. The prevalence of infection, mean intensity, and mean
abundance were calculated using the formulas mentioned in Section 2.6. Photographs of
each trematode parasite are shown with their names in Figure 1b.
Table 4. Infection rate of each fish species for each trematode parasite.
Table 5 lists the infection rate of individual fish species for each monogenean parasite
including Ancyrocephalus sp., Dactylogyrus sp., Gyrodactylus sp. The number of infected fish
with a certain number of monogenean parasites is also listed. The prevalence of infection, mean
intensity, and mean abundance were calculated using the formulas mentioned in Section 2.6.
Photographs of each monogenean parasite are shown with their names in Figure 1c.
Microorganisms 2023, 11, 1940 12 of 16
Table 5. Infection rate of each fish species for each monogenean parasite.
4. Discussion
The significance of continuous surveillance of foodborne parasites and their epidemio-
logical dispersion cannot be overstated in developing countries. Parasites cause pathogenic
effects and financial damage to fish farming. The data in this study indicated the dis-
tribution of parasites in freshwater fish that were collected from three study sites along
River Ravi (shown on the map). The fish diagnosed for parasite infestation were Labeo
rohita, Hypophthalmichthys molitrix, Ctenopharyngodon idella, Cirrhinus mrigala, Cyprinus carpio,
Wallagu attu, Notopterus notopterus, Sperata seenghala, and Oreochromis niloticus. During the
fish investigation, nine protozoan parasites, 11 trematode parasites, and 6 monogenean
parasites were observed under the microscope. A similar study was conducted in Turkey
on the host–parasite relationship, which examined protozoa (14 species), monogenean (12),
and trematode (15) parasites and some other taxa [11]. Similarly, another investigation was
carried out in Bangladesh on the prevalence of protozoan and monogenean parasites in fish
(H. molitrix, C. idella, C. carpio, B. gonionotus, C. catla, L. rohita and C. cirrhosis) by [1], and
two species of protozoan parasites (Trichodina and Chilodonella) and one species of mono-
genean parasites (Dactylogyrus) were examined. The results of the preSSsent study showed
some dissimilarities with [1] because Trichodina was not observed in any fish, and some
other parasites were also identified in our study. Another study was performed by [40] on
large-sized silver and common carp. Their findings identified two protozoans (Trichodina
and Ichthyophthirius multifiliis), two monogeneans (Dactylogyrus and Gyrodactylus), and
two crustacean parasites, which is pertinent to this study because the majority of parasites
were seen in large-sized fish. The photographs of parasites in Figure 1 were similar to the
findings of [9,31,33,35–38]. In this study, the majority of parasites were found in L. rohita,
followed by H. molitrix, C. idella, O. niloticus, C. carpio, and W. attu.
This study examined protozoan parasites including Coccidia, Piscinoodinium, Microsporidia,
Icthyophthirus multifillus, Costia, Ichthyobodo necator, Cryptobia, Chilodonella, and Entamoeba
histolitica. The prevalence of infection, mean intensity, and abundance of protozoan para-
sites that infected the fish is mentioned in Table 3. In [41], an investigation was carried out
on 11 protozoan parasites that had infected Clarias gariepinus. Out of the eleven protozoan
parasites, four parasites were also identified in this study, including Piscinoodinium, Coccidia,
Chilodonella, and Microsporidians. Another protozoan parasite, Costia, was also identified
in the findings of [13,41]. In [42–48], it was reported that Trichodina and Ichthyophthirius
multifiliis were the prevalent protozoan parasites on the skin and gills of cyprinid fish.
In the present study, Ichthyophthirius was observed in rohu and silver carp. In [49], the
authors described chronic infections of catfish by the protozoan parasite Ichthyophthirius
on skin and gills, Ichthyobodo and Chilodonella on the skin, and Cryptobia in the stomach
and intestine. As compared to [49], the present study identified that Ichthyophthirius was
Microorganisms 2023, 11, 1940 13 of 16
present in intestine, Chilodonella was identified on skin, and Cryptobia was identified in
the intestine. In [11], the authors identified harmful protozoan parasites and their infections,
such as Trichodina, Tetrahymena, Ichthyophthirius, and Ichthyobodo necator. This work
showed closeness with the current study because the protozoan parasite Ichthyophthirius
and its prevalence was identified in different fish species. Our results relate to the findings
of [50], which found most protozoan parasites in the intestine. A decline in protozoan
parasites in the stomach was found to be due to the acidic nature of the stomach because
protozoan parasites occupy a specific pH medium [51,52].
This study examined monogenean parasites including Dactylogyrus limipopoensis,
Dactylogyrus anchoratus, Dactylogyrus myersi, Dactylogyrus vastator, Gyrodactylus salaris,
and Ancyrocephalus (mentioned in Table 3). The highest prevalence of parasites was ob-
served in Labeo rohita. Gyrodactylus salaris was first discovered in farmed salmonids in
Romania [53,54]. In the present study, Gyrodactylus was observed in carp. According
to [47], 70 species of Dactylogurus were reported in both wild and farmed common carp in
Iran. In the present study, four species of Dactylogyrous (D. limipopoensis, D. anchoratus,
D. myersi and D. vastator) were observed in the following freshwater fish from River Ravi:
Hypophthalmichthys molitrix, Labeo rohita, Cyprinus carpio, and Oreochromis niloticus. A study
by [44] reported that D. anchoratus and D. extensus were observed within a specific range
of water quality parameters. Furthermore, [55] described that infection with a monoge-
nean parasite could be dangerous and harmful for fries in hatcheries. The results of the
present study also coincide with the findings of [40], which reported that two monogeneans,
Dactylogyrus ssp. and Gyrodactylus, were observed in H. molitrix and C. carpio. These results
are in conformance with [46], who investigated Dactylogyrus sp. and Gyrodactylus in Channa
pleurophtalma in terms of their dominance on the gills.
This study examined trematode parasites including Fasciola hepatica, Trematode Soldier,
Haplorchis pumilio, Brachylaima cribbi, Echinostoma cinetorchis, Clinostomum marginatum,
Deropegus sp., Neascus sp., Fasciola gigantica, Echinostoma revolutum, and Centrocestus for-
mosanus. A microscopic examination of endoparasites of commercially important fish
from Egypt was performed by El-shahawy, in which only one trematode and two cestodes
were identified, while in the present study, none of the cestodes was observed. A study
by [35] identified the infection of many fish species with metacercariae from four species
of trematodes. In the present study, two trematode parasites were identified in freshwa-
ter fish that resemble the findings of [35], including Haplorchis pumilio in the intestine of
grass carp [56] and Centrocestus formosanus in the intestine of silver carp [57]. Haplorchis
pumilio was detected in the intestine of grass carp from the Lower Bari Doab Canal. Thien
et al. (2009) analyzed the same parasites in catfish. Metacarcaria of C. formosanus were
also observed in fish during a study by [58–60]. Two species belonging to two genera of
zoonotic trematode parasites were recorded with different prevalence rates (Centrocestus
formosanus, Centrocestus sinensis, Haplorchis taichui, and Haplorchis pumilio) in various fresh-
water fish species from local markets in northern Vietnam [61], while in the present study,
only one species from both genera was observed. Two trematode parasites, Clinostomum
marginatum and Neascus sp., observed in the present study also relate to the findings of [62].
In the present study, it was also found that large-sized fish had more parasites than smaller
fish. This parasitic load in bigger fish was suggested to result from being exposed to a
variety of parasites while foraging for food [42]. It was also found that the majority of
parasites was observed at the Okara site.
5. Conclusions
A wide diversity of protozoan, trematode, and monogenean parasites was observed in
different organs of freshwater fish species. The highest burden was of protozoans in carps,
which can cause serious detrimental effects on fish health and the economy. Documentation
of these parasites is important to determine their ecological role and the economic value of
the losses they cause in natural waters. The identification of fish parasites and their density
Microorganisms 2023, 11, 1940 14 of 16
and diversity is very important to correctly determine the infectious agents and to assess
the safety techniques used to improve natural fauna and flora in better way.
Author Contributions: Methodology, B.N.K., A.A., I.A., H., M.S.A., I.K., A.A.K.K., B.A., N.M. and
M.A.; Software, R.A.M.; Investigation, A.S.; Resources, M.H.-u.-R.; Supervision, F.A. All authors have
read and agreed to the published version of the manuscript.
Funding: The authors extend their appreciation to Researchers Supporting Project number (RSP2023
R119), King Saud University, Riyadh, Saudi Arabia, for funding this work.
Institutional Review Board Statement: All methods in this work were carried out in accordance with
the “National Biosafety Guidelines” of the Pakistan Environmental Protection Agency, Ministry of
Environment, Government of Pakistan. URL: http://www.environment.gov.pk/images/guidelines/
BiosftyGlines2005.pdf (accessed on 10 July 2023). All experimental protocols were approved by the
Ethical Review Committee, University of Veterinary and Animal Sciences (UVAS), Pakistan. URL:
http://www.uvas.edu.pk/doc/directorates/2014/Research/Guidelines-Protocols.pdf (accessed on
10 July 2023).
Data Availability Statement: Not applicable.
Conflicts of Interest: The authors declare no conflict of interest.
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