Myxozoan Infestation in Freshwater Fishes in Wetlands and Aquaculture in Punjab ( India )

| This article reviews the work done on the myxozoan parasites infesting freshwater fishes in 3 wetlands of Punjab i.e. Harike, Kanjali, Ropar wetlands and also aquaculture fishes in Punjab. A recent study conducted by author and co-workers have reported many pathogenic species infesting aquaculture fishes in Punjab. A large number of important commercial fishes in natural and cultured habitat are vulnerable to various infestions, out of which myxozoans are emerging as the major group. Infestion rate has been recorded to be 34.71% in wetlands and 26.28% in aquaculture. Predominate genera are Myxobolus Buetschli, 1882 followed by Thelohanellus Kudo,1933 infesting gills, operculum, buccal cavity, nasal chamber, eye ball, skin of snout, fins, scale, gall bladder and wall of the alimentary canal. The present document provide the tabulated list of host and myxozoan parasites infesting carp and catfishes in wetlands and cultured ponds of Punjab, India. The most susceptible fish host has been recorded to be Labeo rohita infested with as many as 18 species of myxozoans followed by Cirrhinus mrigala (14 species), Catla catla (12 species), Labeo calbasu (11 species) and Cirrhinus reba (8 species). Fishes in Kanjali wetland have been found to be more infested (29.6%) in comparison to Harike wetland (24.4%) followed by Ropar wetland (20.4%).

Myxozoans are one of the economically important groups of microscopic metazoan parasites as they infest edible fish.New myxosporean pathogens are continually emerging and threatening the development of pisciculture all over the world.They cause production losses and some fish have to be discarded because they are unsightly and not considered to be fit for human consumption.Myxozoans undergo a complex, multicellular development, culminating in the formation of

Historical review
There had been lots of twist and turns in the classification of these organisms.Early classifications by Buetschli, 1882 andDogiel, 1965 placed myxozoans with the Microspora and with parasites now comprising the phylum Apicomplexa (Levine, 1970), together in the class Sporozoa.As the complexities of life cycle were better understood, the class Sporozoa was subsequently referred only to the apicomplexans while the Microspora and Myxozoa remained together in the phylum Cnidospora (Doflein, 1901).More recently, following recognition of profound differences in the ultra-structural composition of these parasites, the Microspora (Sprague, 1977) was raised to the rank of phylum and was found by molecular phylogenetic techniques, to be representative of one of the earliest branching eukaryote lineages (Vossbrinck et al., 1987;Sogin et al., 1989).This had left Myxozoa to stand alone as a phylum without obvious phylogenetic affinities to other protists.Recent developments in myxozoan biology rekindled interest in this group, as it has now been well documented that parasites that were once thought to comprise 2 separate classes, Myxosporea (Butschli, 1881) and Actinosporea Noble in Levine et al. (1980), the latter in fact represented the alternating developmental stage in the life history of a single species.Wolf and Markiw (1984) established that the actinosporean genus "Triactinomyxon" is an alternating stage in the life history of species of Myxobolus.The repeatability of these findings led to a complete reconsideration of the systematics of the group, heralded by Kent et al. (1994) as the "demise of a Class of Protists," namely the class Actinosporea.Smothers et al. (1994) made phylogenetic analysis of the first myxozoan based on SSU rDNA confirming the marginalized suppositions of earlier authors (Stolc, 1899;Weill, 1938) that myxozoa are multicellular organisms and placed myxozoans within the metazoan.Siddall et al. (1995) remarked that phylogenetic position of the myxozoa within the metazoan was uncertain due to the weakness of SSU rDNA data.There is still debate as to which metazoan group myxozoans are most closely related, whether to radially symmetrical cnidarians such as jellyfish, corals etc. (Smothers et al., 1994;Siddall et al., 1995;Hanelt et al., 1996;Siddall and Whitting, 1999) or to the bilateral animals such as nematodes, flatworms etc. (Okamura et al., 2002;Zrzavy and Hypsa, 2003) as they have characteristics of both of them.Monteiro et al. (2002) discovered that Buddenbrockia plumatellae, a worm-like parasite, is a myxozoan and strengthened the case for its bilateral origin, as body plan was superficially similar.However, Siddall et al. (1995) emphasized that functional relationships between polar capsule/filaments and nematocysts argue more for an association with cnidarians.According to National Center for Biotechnology Information, myxosporeans are currently classified as the Myxozoa and are closely related with phylum Cnidaria (Szczepaniak et al., 2010).

life cycle
The life cycles of only 25 myxozoan parasites are known (Kent et al., 2001).Wolf and Markiw (1984) discovered myxosporean life cycles alternating between two host species.With few exceptions, the life cycle of myxozoans include two alternating hosts, an aquatic invertebrate (an oligochaete or a polychaete worm or a bryozoan and a vertebrate host, mainly teleost fish.The myxospore is ingested by an annelid/bryozoan, which undergo schizogony and gametogony and develop in to an actinospore, a triradiate stage.The waterborne actinospores are released from oligochaetes and infect fish via gills or skin.Amoeboid sporoplasm containing the infective secondary cells leaves the actinospore valve, construct and actively penetrate the host integument.In the respective tissue, sporoplasm released from the actinospore divide by endogony and undergo presporogonic multiplication.

spore MorpHology
The vegetative structures offer no distinctive morphological features, classification has been based solely on the structure of spores (Lom and Arthur, 1989).Myx- ozoan spores have proteinaceous shell valves, nematocysts-like polar capsule(s) with coiled extrusible polar filament(s) and an amoeboid infective sproplasm.Spores are uniformly small sized, 10-25µm long but valvular extension(s) attain lengths of 30-60 µm and have 2-3 shell valves.Valves are joined along a thickened suture which is sinuous or straight.The actinospore may have size up to 300µm.The polar filament(s) are for anchoring function.

classification
More than 2,180 species in 60 genera belonging to the Class Myxosporea of the Phylum Myxozoa has been described (Lom and Dykova, 2006).However, three more genera i.e.Soricimyxum fegati from liver of Sorex araneus Prunescu et al., 2007, Gadimyxa atlantica from urinary system of Gadus morhua Koie et al., 2007 and Thelohanelloid bengalensis from gall bladder of Arius sagor Sarkar, 2009 have been described subsequently.Myxobolus is the most common genus reported worldwide which include 744 species (Eiras et al., 2005).The second Class i.e.Malacosporea include only two genera (Tetracapsuloides and Buddenbrockia) with total four described species (Table 1).
Myxobolus is the genus with the greatest number of species and many of these are reported as pathogenic to fish (Kent et al., 2001;Feist and Longshaw, 2006).
Probably the most frequently cited example of myxozoan parasitism is the whirling disease, caused by M. cerebralis (Hedrick et al., 1998).In this case, the parasite infects the cartilages of the host's head and spine, causing deformities that result in the characteristic whirling behaviour.Others that are associated with host mortalities are Tetracapsuloides bryosalmonae, the cause of proliferative kidney disease in Pacific salmon (Kent et al., 2001), Enteromyxon leei, an intestinal parasite of Mediterranean sea bream (Diamant, 1992) and Henneguya ictaluri in pond-reared catfish (Pote et al., 2000).Importance of genus Henneguya as pathogen of freshwater fish has been described by several authors such as Pinto (1928a,b), Jakowska and Nigrelli (1953), Dykova andLom (1978), Kalavati and Narasimhamurti (1985), Martins and Souza (1997), Martins et al. (1999), Hallett and Diamant (2001).Hemananda et al. (2008) reported Henneguya manipurensis as the main cause of ulcerative disease syndrome in freshwater fish Anabas testudineus of Manipur, (India).
Recently, Kaur et al., (2013 a, b;2014) reported pathogenic effects of some myxozoan parasites affecting gills of cultured carps.Multilocular gill infections were found which were of two types viz., intralamellar (LV) and intrafilamental vascular type (FV) causing necrosis, hemorrhage, reduction in respiratory surface (about 15-20% of total gill filament).In the case of infection in the scales the plasmodia were embedded within the layers and, in the case of fins and fin rays the plasmodia were located on the surface as well.

Fetherman et al. (2014) introduced resistant varieties of trout by crossing the German rainbow (GR) and
Colorado River rainbow (CRR) and demonstrated that these could survive and reproduce in rivers with high prevalence of M. cerebralis.

Zoonosis
As regard to the zoonosis of myxozoans they are not considered to be of human health risk, because they do not have been shown to infect human beings.

MYXOZOAN PARASITES OF FRESHWATER FISHES IN PUNJAB
In North India, Gupta and Khera (1987a, 1988a,b,c,d, 1989a,b, 1990, 1991) (1986).Gupta and Khera (1987b) reviewed the genus Henneguya to remove the existing confusion in the literature giving the basic differences between genus Henneguya and Unicauda.Some of the species which were misplaced under the genus Unicauda were transferred to Henneguya.Gupta and Khera (1988c) also transferred all the 18 species belonging to the Myxosoma from Indian freshwater fishes to the genus Myxobolus.

CONCLUSIONS
Existing knowledge on the phylum Myxozoa-an enigmatic group of organisms is fragmentary, inadequate and incomplete in many parts of India especially in the state of Punjab having rich fish biodiversity.
There is great need to identify, describe and satisfactorily classify these parasites both morphologically and at the molecular level.It is evident that study on this group is also important in identification of the pathogenic species which can pose serious threat to fisheries in state of Punjab.This knowledge will help in diagnostics, management and treatment of the diseases caused by these parasites in freshwater fishes.

REFERENCES
• );Madhavan et al. (2013)  have contributed significant number of species from freshwater and marine fishes belonging to genera Myxobolus, Thelohanellus, Myxidium and Henneguya.Basu and

Advances in Animal and Veterinary Sciences September 2014 | Volume 2 | Issue 9 | Page 491
Lomosporus indicus found infecting gills of freshwater fish Labeo calbasu, however, Lom and Dykova (1992) later on synonymised it as the genus Neothelohanellus Das and Haldar recorded 25 species belonging to genera Henneguya, Myxidium, Thelohanellus and Unicauda infesting freshwater fishes.In addition, they also reported a new genus

in Animal and Veterinary Sciences September 2014 | Volume 2 | Issue 9 | Page 497
Two new species of myxosporidians, Myxosoma channai n. sp. and Myxobolus tripathii n. sp., from freshwater NE US