INTRODUCTION:
Cold-blooded vertebrates, or aquatic organisms with the greatest diversity, are the fishes (Phylum: Chordata). Fins are used for swimming, and gills are used for breathing. According to Tedesco et al. (2017), a variety of fish species have effective bodies that allow them to move convincingly in water and defend themselves with scales. According to Leveque et al. (2008), there are approximately 28,900 species of fish worldwide. Of these, 13,000 are classified as freshwater species and are found in rivers, lakes, and other bodies of water. These freshwater species comprise 170 families and 2,513 genera. The other 16,000 species are found in saltwater environments, which make up 70% of the planet’s surface. The parasitic risks that fish farms face globally are discussed in this chapter.
Parasitic fauna of fish;
Various parasites can damage fish directly or indirectly, leading to a high mortality rate within this species. Fish infections are mostly caused by four primary types of parasites: nemathelminthes, acanthocephala, platyhelminthes (monogenean, digenean, cestodes), and protozoa (ciliates, flagellates, microsporidians, and myxozoans). Fish physiology contributes to the spread of deadly infections that cause large-scale deaths (Al Marjan and Abdullah 2009; Lerssutthichawal et al. 2015). Additionally, gastrointestinal (GI) helminths, which are major fish parasites and cause significant losses to the fish industry, are among the many parasites that host fish.In addition to seriously harming the neurological system and preventing fish from reproducingnormally, parasites also interfere with the nutrition, metabolism, and secretory processes of thedigestive system. The main cause of the fish population decline is the threat posed by parasites.(Habib, 2007).Parasitic fauna infecting various systems of fish is given in Table 1
Parasites of vascular system;
| 1 | Sanguinicola | Heart | Perca jlavescens | Sanguinicoliasis | (Muzzall 2000) |
| 2 | Paradeonta cylix | Heart | Greater amberjack | Blood fluke disease | (RepullésAlbelda 2008) |
| 3 | Cardicol | Blood | Northern Bluefin tunna | Blood fluke disease | (Shirakashi 2016) |
| 4 | Trypanoplasma sp. | Vascular system, kidneys | Blue tilapia fish | Blood fluke disease | (Carrington 2017) |
| 5 | Crassiphiala | Blood | Vermont fish | Blood fluke disease | (Achatz 2019) |
| 6 | Aporocotylid digenean | Heart, Gills, Cranial & mesenteric Blood vessels | Fresh and marine water fish | Black grub | (ddubnaya2021) |
Parasites of viscera and musculature;
| 1 | Contracaecum rudolphii | Body Cavities & visceral | All types of fishes | Whirling disease | (Alexander 2020) |
| 2 | Sphaerospora renicola | Kidneys | Cyprinids | Renal dropsy | (Eszterbauer and Székely 2004) |
| 3 | Posthodiplostomu mcuticula | Viscera, Heart & Posterior kidney | Freshwater fishes | Black spot disease | (Ondračková 2004) |
| 4 | Diphyllobothrium latum (Broad fish tapeworm) | Viscera & Musculature | Fresh water fishes | Diphyllobothriasis | (Scholz 2009) |
| 5 | Proteocephalus ambloplitis | Ovary | Freshwater fishes | Diphyllobothriasis | (Scholz 2019) |
| 6 | Bolbophorus confuses | Skeletal muscle & Viscera | Channel catfish | Channel virus disease or enteric septicemia like condition | (Doffitt 2020) |
| 7 | My. cerebralis / M. cerebralis | Head, Cartilage & backbone | Salmon and trout | Whirling disease |
| 1 | Glugea (Gl.) hertwigi & Gl. Stephani | Submucosa of GI & Mesentery | Smelt, marine flatfishes | Nonfunctional, granulomatous bulged out abdomen | (Ogawa 1998) |
| 2 | Bothriocephalus acheilognathi | Intestine | Carps and other cyprinids | Haemorrhagic enteritis/ Gowkongensis Gowkongensis | Maldonado2003 |
| 3 | Cryptobia iubilans | Stomach | African cichlids | Cryptobiosis | (Woo 2003) |
| 4 | Balantidium | Intestinal lumen | Marine and Fresh-water fish | Catarrhal enteritis and ulceration | (González 2005) |
Parasites of the alimentary canal;
| 5 | Goussia (G.) subepithelialis, G. Carpelli | Intestinal epithelial cells | Carps, | Coccidiosis | (Pasnik 2005) |
| 6 | Cryptosporidium | Stomach | Marine tropical fish | Cryptosporidiosis | (MéndezHermida 2007) |
| 7 | CeratomyxaShasta | PosteriorIntestine | Salmonids | Ceratomyxosis | (Bjork 2010) |
| 8 | Pseudophyllid | Intestine | Wild and cultivated salmonids | Chronic haemolytic Anaemia | (Hoole 2010) |
| 9 | Spironucleus | Intestin | Salmonids, All cichlids, bettas, gouramis, other aquarium snd freshwater fishes | “Hole in the head” disease | (Williams 2011) |
| 10 | Caryophyllidea | Intestine | Cyprinid and catostomid fish | Intestinal nodules and ulcer | (Barčák 2014) |
| 11 | Contracaecum | Alimentary tract | Largemouth bass, centrarchids | Anisakidosis | (Younis 2017) |
| 12 | Camillanus | Alimentary tract | Largemouth bass, other centrarchids | Anisakidosis | (Manickam 2018) |
| 13 | Philometra | Body cavity, Tissues & Ovaries | Marine fish | “Parasitic Castration” in female fish | (Ali 2018) |
| 14 | Eustrongylides | Viscera & Muscles | Angelfish | Eustrongylidosis | (Guagliardo 2019) |
| 15 | Capillaria | Intestine | Angelfish, discus, other aquarium fish | Capillariasisis | (AbdelRahman 2019) |
| 16 | Crepidostomum Palearctic regions | Intestine | Salmonids In the Nearctic and | Enteritis | (Picard‐ Sánchez 2020) |
| 17 | Enteromyxum (E.) leei, E.scophthalmi | IntestinalEpithelium | Tiger puffer fish, marine and freshwater fish | Enteritis | (Picard‐ Sánchez 2020 |
| 18 | Acanthocephalus | Intestinal lumen | Wildcaught freshwater | Necrotic haemorrhagic Ulcers | (Nakao 2021) |
Helminths parasites of fish;
The majority of parasites that infect fish are called helminths. Both freshwater and marine fish are being infected by more than 30,000 different helminth species, a number of which are known to cause severe diseases in fish or to pose a significant risk to public health (Williams and Jones 1994). The three main types of helminth parasites are Platyhelminthes (flatworms: cestodes, monoge-neans, and digeneans), Nemathelminthes (roundworms: nematodes), and Acanthocephalan (thorny-headed worms).(Nguyen et al. 2020)
Trematodes;
Trematodes are a class of helminths that are further divided into monogeneans and digeneans. Flatworms and flukes are other names for this group of organisms. The skin, fins, and gills of freshwater and brackishwater teleosts are the sites of infection for these organisms. (Antar and Gargouri 2018).
Monogeneans;
Monogeneans are host-specific by nature (Saad-Fares 1992). They have sensitive systems, a mouth with or without auxiliary suckers, unique glands, and clamps for attaching to the host at the anterior end. They are hermaphrodites. They mostly live on the host’s body surface, such as the nares, branchiostegal membranes, lip folds, scales, fins, and gills. They do not require an intermediary host to participate in their direct life cycle.(Buchmann 2002).The parasite that infects carp fry fish is called Dactylogyrus (D.) vastator. It causes epithelial hyperplasia in the gills of the host, interfering with the respiratory system and ultimately killing the animal. Additionally, D. extensus is a lethal parasite that affects both adult and juvenile fish (Dzika 2009). D. groschefti has demonstrated that young Clarias gariepinus have mortality rates of almost 90%. (Hansen 2003).The majority of farmed fish affected by macroglossidactylus include the species of Clarias, Lates niloticus, and Anabantidae (Iyaji 2008). An infestation of parasites is influenced by various chemical and physical variables. The pond’s depth and temperature are examples of its physical characteristics; its salinity and oxygen concentrations are its primary chemical characteristics. Seasonal parasite prevalence is primarily influenced by temperature (Gopko 2020).
Nematodes;
In Africa, there are forty different types of nematodes that seriously infect different fish species’ digestive systems. Typically, adult nematodes live in the digestive system of fish. However, depending on the specific nematode species and infected fish, distinct life stages may be present in the swim bladder, the inner organs, coelomic cavity, exterior muscle layers, inside the skin, or inside the fins (Dick and Choundury 1995). From 15 different species of fish found along the Karachi coast, 13 different species of nematodes—eight of which are new—were found in Pakistan. Anisakis simplex, Tetrahymena corlissi, and Camallanus cotti were the most often observed nematodes in the intestine of wild marine animals. (Khan and Begum 1971). Nematodes are frequently found in small quantities in healthy fish, but their population can grow to the point of grave sickness or even death. The nematode will enter another organism, usually a marine invertebrate such as a side swimmer, side copepod, or insect larva, if the fish is the ultimate or final host. There, it will grow until it is consumed by a fish. Nematode species infect fish and undergo sexual maturation and reproduction after ingestion. The fish is identified as the ultimate or final host in this scenario. (Ali et al. 2014)
Some significant parasites of fish;
Cryptocaryon irritans;
Numerous fish species have been documented to contract Cryptocaryon infections, and distinct strains of the virus have been identified from throughout the globe. Many of them are outside of the previously stated “normal” ranges, even if some of them share many traits, such as life cycles and salt tolerances. (Yambot et al. 2003).As it ages, the tomont splits into different tomites. The length of the entire life cycle can vary based on a number of variables, such as the fish host, temperature, salinity, and parasite strain (Yambot et al. 2003; Rigos et al. 2013). The life cycle has been shown to last an average of one to two weeks, but it can last up to eleven weeks. Tomont maturation uncertainty is the reason for this diversity in the life cycle.(Dickerson 2006). Due to the variety of C. irritans strains, the temperature and salinity of the water, or perhaps because different fish species act as hosts, the amount of time needed and the size at different life cycle phases may vary. Most Cryptocaryon strains thrive best in temperatures between 23 and 30 degrees Celsius.(Wang et al. 2018).
Trichodinas;
One of the frequent parasites that live in freshwater and marine environments on fish, whether they are cultivated or wild, is Trichodina. According to Martins and Ghiraldelli (2008), these parasites are also referred to as ciliated protozoans and ecto-commensals. Almost 300 different kinds have been documented worldwide thus far, originating from various habitats (Tang and Zhao 2012).
Ichthyophthirius multifiliis
The ciliated protozoan Ichthyophthirius (I.) multifiliis is an obligatory parasite that inhabits warm, humid environments in freshwater fish. Its eruptions occur between 15 and 25 °C (Noga 2014). High mortality and financial ruin are the results for different food fish raised inaquaculture. Additionally, it has an impact on a number of aquaculture species, such as ornamental fish, hatcheries, striped catfish, snow trout, rainbow trout, channel catfish, and grass carp (Mallik et al. 2015, Kumar et al. 2018).
Brooklynella hostilis;
The cause of Brooklynellosis, often known as slime-blotch or clownfish illness, is Brooklynella (B.) hostilis. Most teleosts in a marine aquarium are infected with B. hostilis. It is a kidneyshaped creature with bands of cilia that range in length from 60 to 80 µm. B. hostilis is a member of the monotypic Brooklynella genus, which has just one species, in the order Hartmannulidae. It requires dead skin to reproduce, damages gills severely, and replicates via binary fission (Fioravanti and Florio 2017). The parasite multiplies quickly and is easily transferred to a new host. These microscopic protozoa have the ability to enter a more developed host or, more often, they attach themselves to the host that their parents were living on(Anshary 2020).
Myxozoan parasites;
Myxozoans are protozoan parasites that inhabit both fresh and saltwater environments and mostly impact the gastrointestinal tract of different species of fish. Enteromyxum (E.) leei is the parasite that is most prevalent among these. E. scophthalmi is another significant myxozan parasite that is known to transmit directly and that generates similiar intestinal conditions in the gastrointestinal tract of turbot fish species (Redondo et al. 2004).
Contracaecum rudolphii;
A nematode parasite called Contracaecum rudolphii affects a number of fish species, including Gobio gobio, Cyprinus carpio, Alburnoides bipunctatus, Anguilla anguilla, Barbatula barbatula, Perca fluviatilis, Phoxinus phoxinus, Poecilia reticulata, and Tinca tinca (Moravec 2009). It can infect fish either directly or indirectly, for example, by infecting copepods that the fish eat. There are three larval phases in its life cycle, with the parasite’s infectious stage occurring in the third stage. It enters the bodily cavity through the intestinal wall and encysts the visceral organs (Baruš 2001).
Refrences;
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Leveque et al., 2008. Global diversity of fish (Pisces) in freshwater. Hydrobiologia 595: 545-567.
Lerssutthichawal et al., 2015. Monogeneans of potentially cultured Tilapias and first record of Cichlidogyrus mbirizei in Thailand. Journal of Science and Technology 13: 543-553.
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Occurrenceof Sanguinicola occidentalis in Perca flavescens and Campeloma decisum from a Michigan creek. Journal of Parasitology 86: 1360-1362.
Repullés-Albelda AM, 2008. Speciation of the Paradeontacylix spp. (Sanguinicolidae) of Seriola dumerili. Two new species of the genus Paradeontacylix from the Mediterranean. Parasitology International 57: 405-414.
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Achatz TJ, 2019. Phylogenetic relationships expanded diversity and distribution of Crassiphiala spp. (Digenea, Diplostomidae), agents of black spot disease in fish. Parasitology Research 118: 2781-2787.
Eszterbauer E and Székely C, 2004. Molecular phylogeny of the kidney-Parasitic Sphaerospora renicola from common carp (Cyprinus carpio) and Sphaerospora sp. from goldfish (Carassius auratus auratus). Acta Veterinaria Hungarica 52: 469-478.
Hoole DC, 2010. Ligula intestinalis (Cestoda: Pseudophyllidea): An ideal fish-metazoan parasite model? Parasitology 137: 425-438. Williams CF, 2011. Spironucleus species: Economically important fish pathogens and enigmatic single-celled eukaryotes. Journal of Aquaculture Research and Development DOI:10.4172/2155-9546.S2-002.
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