Skip to main content
NCBI home page
Journal of Parasitic Diseases: Official Organ of the Indian Society for Parasitology logoLink to Journal of Parasitic Diseases: Official Organ of the Indian Society for Parasitology
. 2018 Oct 30;43(1):14–21. doi: 10.1007/s12639-018-1031-x

First report of Posthodiplostomum minimum metacercariae and resulting histopathological changes in Bagrus bajad from Lake Nasser, Egypt

Awatef H Hamouda 1, Eman K A Bazh 2,✉
PMCID: PMC6423241  PMID: 30956440

Abstract

Parasitological studies of 100 Bagrus bajad fish were collected from Lake Nasser, Aswan, Egypt. Out of them 75 were infected with metacercariae in two forms; encysted in most visceral organs and free only in air bladder. These were identified morphologically as Posthodiplostomum minimum metacercariae (Strigeidida: Diplostomidae). The intensity of white grub in B. bajad was high in the intestine (30 encysted metacercariae/g). The highest prevalence season observed in summer and the lowest in winter. The histopathological examination revealed encysted metacercariae of different sizes within the intestinal musculature accompanied with granular infiltration with eosinophilia. Degenerative changes were observed in liver and kidney cells, as well as congestion of hepatic sinusoids. Spleen showed both lymphoid and melanomacrophages cells depletion.

Keywords: Metacercariae, Diplostomidae, Posthodiplostomum minimum, White grub, Bagrus bajad, Histopathology

Introduction

Diplostomidae are worldwide distributed digeneans parasites of high importance, required three different hosts to complete their life cycle; snails and a wide range of fish as first and second intermediate hosts respectively as well as, piscivorous birds and mammals as final hosts (Choudhary et al. 2017). This family contains different species of Posthodiplostomum (Dubois 1936). The metacercariae of Posthodiplostomum cuticola causing “neascus” or “black spot” disease in fish (Karimian et al. 2013) and Posthodiplostomum minimum (MacCallum 1921) encysts in viscera and sometimes in musculature of fish given what is known “white grub” (Grizzle and Goldsby 1996; Lane and Morris 2000; Lane et al. 2015; Boone et al. 2018). The penetration of large numbers of the P. minimum cercariae into a fish may cause its death especially during the first few days after infection (Meade and Bedinger 1967). Fish mortality is expected when the liver is damaged by the metacercariae (Lane and Morris 2010).

P. minimum grubs have an adverse effect on the fish; reducing their growth rate, loss the condition of the infected fish and impair the immune functions leave the fish more susceptible to a variety of secondary diseases (Grizzle and Goldsby 1996) as well as, visible P. minimum parasites render the fish undesirable by the consumers.

Bagrus bajad (Forsskål 1775) is a siluriformes freshwater fish in the family: Bagridae, inhabits many lakes, swamps and rivers in Africa including River Nile. B. bajad lives and feeds on or near the bottom. Adults are piscivorous, prey on small fish, particularly Alestes spp. Also, B. bajad feeds on insects, crustaceans, mollusks and vegetable matter. It is an important food fish in addition to its flesh is of good quality and of economic importance commonly sold as food (Pauly and Froese 2007).

Despite records of P. minimum infections in several fish species, the identification and pathogenesis of this parasite in B. bajad are lacking. So the aim of this study is to characterize the P. minimum of B. bajad, recording the clinical signs, postmortem lesions, predilection sites of metacercariae, intensity of infection in each organ, seasonal prevalence and histopathological features of infected fish.

Material and methods

Study area and fish samples

Lake Nasser is an artificial lake created after the construction of Aswan High Dam on the River Nile in Egypt in the 1960s. It extends 300 km within the Egyptian borders, with a shoreline of about 7000 km and lies between Lat 22°00′–23°58′N and Long 31°19′–33°19′E. It represents the main source of freshwater in Egypt.

100 B. bajad (25 fish/season) of different sizes; total length (30–50) cm and weights (600–1000) gm were collected, alive and randomly, from different localities of Lake Nasser during the period of May 2017 to April 2018. The collected fish were kept in glass aquaria in the laboratory of Fish Diseases, Faculty of Fish and Fisheries Technology, Aswan University.

Clinical, postmortem and parasitological examinations

The investigated fish were subjected to the full clinical examination. They were euthanized rapidly by severance of the head and brain from the spinal cord followed by brain pithing according to AVMA (2013). The procedures complied with local and national animal welfare laws, guidelines and policies.

Detection of the external, internal gross lesions and parasitological examination for detection of free or encysted metacercariae (EMC) were performed according to (Lucky 1977; Woo 1995; Noga 2010).

The body surface, fins, gills, liver, spleen, kidney, stomach, intestine, heart, brain, eyes, air bladder, urinary bladder, gall bladder, mesentery and musculature were examined separately in separate petri dishes containing 0.9% physiological saline with a dissecting microscope. Parts of these organs were examined microscopically by direct compression between two glass slides for any parasitic nodules. The collected parasites were washed, fixed, stained and permanently mounted according to the methods described by (Lucky 1977; Woodland 2006). The density of infection with encysted metacercariae was recorded by taking several slices (1 g) from different parts of each organ tissue. Compress it between two glass slides and count the metacercariae in each gram then calculate the mean (El-Naffar and El-Shahawi 1986). The density of infection with free metacercariae in air bladder was recorded by counting them in each dissected fish then calculate the mean. The obtained results were statistically analyzed using the mean and the standard error of the mean (SEM) by using the SPSS software (SPSS 2007).

The detected free and encysted metacercariae were identified according to (Gibson 1996).

Histopathological examination

Sections of intestines, liver, kidney and spleen of the infected fish were preserved immediately in 10% formalin and processed for histopathological evaluation, using the routine paraffin embedding method as described by Bancroft and Gamble (2007).

Results

Grossly examination of B. bajad revealed the presence of several wounds on the infected fish skin (Fig. 1). While internally, the presence of numerous white small cysts; P. minimum encysted metacercariae in different organs of the infected fish (intestine, stomach, urinary bladder, mesentery, liver, spleen and the kidney) were recorded. Parasitic cyst wall was thin, and delicate. The encysted form was not larger than 1 mm and they reside in and around the fish’s organs. They were not found in the musculature, heart, brain and eyes (Fig. 2). The free metacercariae were isolated only from the air bladder.

The metacercariae were belonging to:

Superfamily Diplostomoidea (Poirier 1886)

Syn. Strigeoidea (Railliet 1919)

Family Diplostomidae (Poirier 1886)

Subfamily Crassiphialinae

Genus: Posthodiplostomum (Dubois 1936))

P. minimum (MacCallum 1921) (Dubois 1936) (metacercaria)

Syn.: Neascus vancleavei (Agersborg 1926).

Fig. 1.

Fig. 1

Open in a new tab

Bagrus bajad from Lake Nasser infected with Posthodiplostomum minimum showing hemorrhagic patches on the caudal peduncle (black arrows)

Fig. 2.

Fig. 2

Open in a new tab

Bagrus bajad showing white spots scattered all over the intestinal tract (arrows) and congested intestine and stomach

The body of free metacercaria was linguiform, obviously divided into two distinct regions by annular constriction; anterior part was scoop-shaped with distinct ventral concavity and posterior part (hind body) was oval to spherical. A pseudosucker was absent. The oral sucker was present normally, while the ventral one may be small. Primordiums of gonads were occasionally visible (Fig. 3). The encysted metacercariae of P. minimum were round or oval in shape, surrounded by two layers; the inner layer being of parasitic origin and the outer layer formed by the host. 1–3 metacercariae may be enclosed in the same cyst. The density of metacercariae per gram was high in the intestine (30/g) and in the urinary bladder (25/g) as in Table 1 and Fig. 4.

Fig. 3.

Fig. 3

Open in a new tab

Posthodiplostomum minimum (free metacercariae). a Unstained specimen × 220, b stained specimen (Carmine stain) × 132. Scale bar = 100 µm. OS oral sucker, CC calcareous corpuscles, VS ventral sucker, PH pharynx, INT intestine, HO hold fast organ, HiB hind body, GP genital primordia, BC bursa copulatrix

Table 1.

Site and density of free and encysted metacercariae of Posthodiplostomum minimum in Bagrus bajad from Lake Nasser during the period of May 2017 to April 2018 (number of infected B. bajad = 75)

Parasite type Site of infection Density/g (M ± SEM)
P. minimum encysted metacercariae Intestine 30 ± 0.4
Urinary bladder 25 ± 0.3
Mesentery 15 ± 0.5
Stomach 10 ± 0.4
Liver 9 ± 0.4
Kidney 8 ± 0.3
Spleen 6 ± 0.5
P. minimum free metacercariae Air bladder Density/dissected fish (M ± SEM)
5 ± 0.3
Open in a new tab

Data represent the metacercariae (as the M (mean) ± SEM standard error of the mean)

Fig. 4.

Fig. 4

Open in a new tab

Posthodiplostomum minimum encysted metacercariae in the urinary bladder wall. X 200. Scale bar = 100 µm. Unstained specimens

The overall prevalence of white grub; P. minimum metacercariae (free or encysted) in the fish was 75%. Intestine, urinary bladder, mesentery, stomach, liver, kidney and spleen were infected with encysted metacecraiae. The free P. minimum metacercaria was collected from the air bladder only. The intestine showed the highest (71%) prevalence of encysted metacercariae while air bladder showed the highest prevalence (70%) of free metaceracariae. spleen showed the lowest infection rate (38%) (Fig. 5) Seasonal occurrence of metacercariae was found to be the highest during summer and the lowest during winter as shown in Table 2.

Fig. 5.

Fig. 5

Open in a new tab

Prevalence of Posthodiplostomum minimum metacercariae in Bagrus bajad from Lake Nasser during the period of May 2017 to April 2018 (examined number = 100)

Table 2.

Seasonal prevalence of free and encysted metacercariae of Posthodiplostomum minimum in Bagrus bajad from Lake Nasser (n = 25/season) during the period of May 2017 to April 2018

Infected organ Season
Spring Summer Autumn Winter
No. % No. % No. % No. %
Intestine 18 72 22 88 16 64 15 60
Urinary bladder 17 68 20 80 15 60 14 56
Mesentery 16 64 20 80 14 56 13 52
Stomach 14 56 18 72 13 52 11 44
Liver 13 52 16 64 12 48 9 36
Kidney 12 48 15 60 11 44 8 32
Spleen 10 40 13 52 9 36 6 24
Air bladder 20 80 23 92 17 68 10 40
Open in a new tab

These numbers means one or more organs were infected in a single B. bajad. Musculature, Heart, brain and eye were free totally from infection

No. number of infected fish

The most prominent histopathological alterations were represented with the presence of different sized encysted metacercariae within the musculature of the infected intestine mostly subserosal. Sections of metacercarial cysts revealed that there were two layers, enclosed them as well as, they may contain more than one metacercariae in the same cyst. The cysts were also seen within normal tissue or associated with deep necrotic changes which mostly associated with inflammatory cells infiltration as eosinophilic granular cells, lymphocytes and macrophages. Other organs such as liver, kidney and spleen showed other secondary degenerative changes. Liver revealed marked ballooning of hepatocytes with peri-portal hepatic necrosis. The spleen showed marked congestion of the hepatic sinusoids with depletion of both lymphoid elements and melanomacrophages cells. Kidney demonstrated features of interstitial nephritis associated with degeneration and necrosis of the renal tubules and infiltration of inflammatory cells including eosinophilic granular cells, lymphocytes and macrophages (Figs. 6, 7).

Fig. 6.

Fig. 6

Open in a new tab

Intestine of Bagrus bajad showing a necrotic changes within the muscle layer accompanied with granular eosinophilic cells infiltration (arrowhead), b parasitic encysted metacercaria burdened within the muscle layer (arrowhead) c parasitic encysted metacercaria burdened within the muscle layer mostly towards the serosal layer (arrow), d live encysted metacercaria within the muscle layer (arrowhead), H&E, X100. Scale bar = 100 µm

Fig. 7.

Fig. 7

Open in a new tab

a Liver of Bagrus bajad showing marked hepatic vacuolation associated with marked fatty degeneration (arrow), b liver showing marked hepatic degeneration mostly within the periportal area (arrow), c kidney showing interstitial nephritis (arrowhead), d Spleen showing marked both lymphoid (arrowhead) and melanomacrophages cells (arrow) depletion, H&E, X200. Scale bar = 100 µm

Discussion

Parasitic fish diseases constitute about 80% of fish diseases in Egypt (Eissa 2006). Which may have negative consequences on fish health by reducing weight gain and increasing mortality rates (Barber and Svensson 2003).

Actually, parasitological studies of B. bajad from Lake Nasser are very scarce and no reports on Posthodiplostomum metacercariae infection among this fish species in the lake. This grub does not attract as much attention as the yellow grub caused by Clinostomum sp. This may be due to it is smaller and encysts in the visceral organs (e.g. the stomach, the intestine, the kidneys, the liver…etc.) rather than throughout the branchial cavity or skin.

Gross examination of B. bajad revealed the presence of several wounds on the fish skin resulted from invasions of cercariae. Posthodiplostomum spp. in fish are complicated infections; need snails as an intermediate host of their propagation and transmission to fish; therefore hemorrhagic patches, wounds and ulcers on different parts of the fish’s body due to blood congestion and hemorrhage at the point of cercaria penetration were always found on the infected fish (Spall and Summerfelt 1970; Ritossa et al. 2013 and Hamouda 2014).

Lane et al. (2015) recorded “white grub” P. minimum metacercariae in many fish species. Boone et al. (2018) detected white grub (P. minimum) metacercariae in the visceral organs of many centrarchids freshwater fishes. Kvach et al. (2017) detected Posthodiplostomum cf. minimum centrarchi (Strigeiformes: Diplostomidae), from seven localities in Europe, recording the cysts in the mesentery and internal organs of two fishes (Lepomis gibbosus and Micropterus salmoides) from sites in Bulgaria, the Czech Republic and Portugal. Zhang et al. (2018) found internal P. minimum cysts in the livers tissues in many North Americans freshwater fishes.

Interestingly, metacecariae of P. minimum were found free unencysted in the air bladder of B. bajad and this was somewhat similar to that reported by Kalogianni et al. (2017) who isolated Posthodiplostomum species from the freshwater fishes in Greece which occurred in two forms; excysted and encysted in the abdominal cavity.

The morphological description of the recovered unencysted P. minimum metacercariae was typically similar to that recorded in Japan by (Nguyen et al. 2012). Also, (Athokpam and Tandon 2014) described the typical morphological features of the genus Posthodiplostomum (e.g. distinctly bipartite body and tribocytic organ was disc-shaped with a median slit) and showed well-developed gonads and anlagen of some genital organs, but no melanin. (Boone et al. 2018) mentioned that P. minimum metacercariae has limited morphological variation among a wide range of hosts.

The recorded results revealed that 75% of the examined B. bajad were infected with P. minimum and this may be due to the abundance of the snails and the presence of piscivorous birds around Lake Nasser all over the year, explains the high prevalence of P. minimum in B. bajad in this area. “White grub” is the metacercarial stage of a fluke (P. minimum) that occurs in many fish species, in 2 centrarchid hosts, bluegill (Lepomis macrochirus) with 100% prevalence and white crappie (Pomoxis annularis) 57%, from Spring Lake in McDonough County, Illinois (Lane et al. 2015). While, in Lower Egypt, at Dakahlyia Governorate (Mansour et al. 2003) did not record any Posthodiplostomum sp. infection in the examined B. bayad which collected from River Nile. McAllister et al. (2016) detected P. minimum in a Redspot Chub (Nocomis asper) from Oklahoma with prevalence of 25%. García-López et al. (2016) recorded P. minimum from different organs of infected fish with prevalence ranged from (2.7--31.60)  %. Calhoun et al. (2018) recorded P. minimum in the liver, heart, kidney and body cavity of some freshwater fishes from California with prevalence of 36.09%. The differences between the obtained results with many studies may be due to, the different localities from which the examined fish were collected and the different water hydrochemistry in each area. Rossiter and Davidson (2018) found that the strongest predictors of P. minimum infection intensity were fish collection site, host body mass and species identity.

The highest prevalence of infection with metacercariae of P. minimum was recorded in summer. This result was of great agreement with Saleh et al. (2009) who recorded encysted metacercariae other than P. minimum from muscle, liver, gonads and gills of B. bayad at Port Said province, Egypt at 77.2% reporting high prevalence in summer, spring, autumn then winter. Also, (Schaaf et al. 2017) suggested that the warmer temperatures are associated with the increase black spot disease prevalence in threatened Steelhead trout in California due to some environmental and biotic conditions.

The intensity of infection in organs was variable ranged from 30/g in intestine and about 5/dissected fish in air bladder of B. bajad. (Mitchell et al. 1982) recorded massive infection of (Pimephales promelas) fish with more than 2000 P. m. minimum metacercariae. On the other hand, (Rabaldo et al. 1999) recorded 6 parasites per tissue section as the high intensity of cysts infection.

The histopathological studies associated with digenean larval stages of P. minimum infection in fish are very scarce. our results showing several changes in the infected organs (intestine, liver, kidney) as inflammatory cells infiltration (eosinophilic granular cells, lymphocytes and macrophages). The infected liver with marked congestion of hepatic sinusoids. This agreed to the results recorded by (Mitchell et al. 1982) who recorded an intensive inflammatory response had resulted from the infection with Posthodiplostomum m. minimum in fathead minnow; Pimephales promelas fish in USA. Mladineo (2006) recorded lymphocytic infiltrations around the parasitic cysts of the digenea Didymocystis spp. declaring that the intensity of observed reaction was depended mainly on the size of the cyst and on the infected tissue. Ramos et al. (2012) recorded that visceral infection of Lepomis gibbosus fish with P. minimum centrarchi revealed numerous cysts present in spleen, liver and kidney which surrounded by a cellular inflammatory response (macrophages, eosinophils and polymorphonuclear neutrophils).

(Reddy and Benarjee 2014) reported that the intestine of Channa punctatus infected with the trematode Genarchopsis goppo showed damage of the villi, inflammation, fibrosis associated with hyperplasia and metaplasia epithelial necrosis.

Liver of infected B. bajad with P. minimum showing marked ballooning of hepatocytes with periportal hepatic necrosis. The degeneration and necrosis of the hepatocytes was resulted from the pressure atrophy of the encysted metacercariae in liver cells and the toxic waste products excreted by these cysts (Ramadan et al. 2002; Shareef and Abidi 2015; Maghrabi 2017).

In the present results, kidney demonstrated features of interstitial nephritis with degeneration and necrosis of the renal tubules and infiltration of inflammatory cells. This agreed with (Shareef and Abidi 2015) who recorded that the infected kidney with digenetic trematode; Euclinostomum heterostomum from Channa punctata showed dilation of renal tubules, vacuolar degeneration, tubular epithelial cells with hypertrophy and hyperplasia, occlusion of tubules, fibrosis, hemorrhage, and congestion of glomeruli.

Conclusion

It is of great interest that, B. bajad from Lake Nasser possess P. minimum metacercariae either encysted in vital organs as liver, spleen, kidney, intestine, stomach, urinary bladder and mesentery or free in air bladder. These metacercariae have adverse effects on these organs which confirmed histopathologically for the first time. P. minimum predispose the infected fish to other diseases (bacterial, fungal, viral) by creating portals of entry when cercariae penetrate the skin to infect fish. The edible part of the fish (musculature) was free from parasitic infection and safe completely for human consumption. This study will be a helpful tool for further investigations about the effects of P. minimum infection on gross rate, fecundity, immunity and survival of this fish species.

Ethics approval

This work was approved by the ethics approval form (3/2017).

Conflict of interest

Authors declared that there is no any conflict of interest.

References

  1. Athokpam VD, Tandon V. Morphological and molecular characterization of Posthodiplostomum sp. (Digenea: Diplostomidae) metacercaria in the muscles of snakeheads (Channa punctata) from Manipur, India. Helminthologia. 2014;51(2):141–152. doi: 10.2478/s11687-014-0221-z. [DOI] [Google Scholar]
  2. AVMA . American Veterinary Medical Association: guidelines for the euthanasia of animals. 2013. Schaumburg: American Veterinary Medical Association; 2013. [Google Scholar]
  3. Bancroft JD, Gamble M. Theory and practice of histological techniques. 5. London: Churchill Livingstone; 2007. pp. 125–138. [Google Scholar]
  4. Barber I, Svensson PA. Effects of experimental Schistocephalus solidus infections on growth, morphology and sexual development of female three-spined sticklebacks, Gasterosteus Aculeatus. Parasitology. 2003;126(4):359–367. doi: 10.1017/S0031182002002925. [DOI] [PubMed] [Google Scholar]
  5. Boone EC, Laursen JR, Colombo RE, Meiners SJ, Romani MF, Keeney DB. Infection patterns and molecular data reveal host and tissue specificity of Posthodiplostomum species in centrarchid hosts. Parasitology. 2018 doi: 10.1017/S0031182018000306. [DOI] [PubMed] [Google Scholar]
  6. Calhoun D, McDevitt-Galles D, Johnson P. Parasites of invasive freshwater fishes and the factors affecting their richness. Freshw Sci. 2018;37(1):134–146. doi: 10.1086/696566. [DOI] [Google Scholar]
  7. Choudhary K, Tripathi A, Pandey KC, Agrawal N. Morphological and molecular characterisation of three Indian Neascus-type metacercariae (Digenea: Diplostomidae) Parasitol Int. 2017;66(5):652–659. doi: 10.1016/j.parint.2017.06.007. [DOI] [PubMed] [Google Scholar]
  8. Eissa IAM. Parasitic fish diseases in Egypt. Cairo: Dar El-Nahda El-Arabia Publishing; 2006. [Google Scholar]
  9. El-Naffar MK, El-Shahawi GAZ. Studies on the metacercariae of the Nile fishes at El-Mini Province, A.R. Egypt. Assiut Vet Med J. 1986;15(30):46–58. [Google Scholar]
  10. García-López M, Salguero-Vargas G, García-Prieto L, Osorio-Sarabia D, Pérez-Ponce de León G. Endohelminths of some species of fishes from Lake Xochimilco, Mexico. Revista Mexicana de Biodiversidad. 2016;87(2016):1360–1364. doi: 10.1016/j.rmb.2016.06.018. [DOI] [Google Scholar]
  11. Gibson DI (1996) Guide to the parasites of fishes of Canada. In: Margolis L, Kabata Z (eds) Canadian special publication of fisheries and aquatic sciences 124. Part IV, Trematoda
  12. Grizzle JM, Goldsby MT., Jr White grub Posthodiplostomum minimum centrarchi metacercariae in the liver of largemouth bass: quantification and effects on health. J Aquat Health. 1996;8:70–74. doi: 10.1577/1548-8667(1996)008<0070:WGPMCM>2.3.CO;2. [DOI] [Google Scholar]
  13. Hamouda AH (2014) Studies on the trematodal and cestodal diseases in cultured freshwater fish in Kafr El-Sheikh Governorate. Ph.D. Thesis, Faculty of Veterinary Medicine, Kafrelsheikh University, Egypt
  14. Kalogianni E, Kmentová N, Harris E, Zimmerman B, Giakoumi S, Chatzinikolaou Y, Vanhove M. Occurrence and effect of trematode metacercariae in two endangered killifishes from Greece. Parasitol Res. 2017;116:3007–3018. doi: 10.1007/s00436-017-5610-z. [DOI] [PubMed] [Google Scholar]
  15. Karimian E, Ghorbani R, Hajimoradlou A. First occurrence and intensity of Posthodiplostomum cuticola (Nordmann 1832) (Digenea; Diplostomatidae) metacercariae in monkey goby (Neogobius pallasi Berg 1916) in the Zarringol stream, Golestan Province, Iran. Global Vet. 2013;10(5):505–510. [Google Scholar]
  16. Kvach Y, Jurajda P, Bryjová A, Trichkova T, Ribeiro F, Přikrylová I, Ondračková M. European distribution for metacercariae of the North American digenean Posthodiplostomum cf. minimum centrarchi (Strigeiformes: Diplostomidae) Parasitol Int. 2017;66(5):635–642. doi: 10.1016/j.parint.2017.06.003. [DOI] [PubMed] [Google Scholar]
  17. Lane RL, Morris JE. Biology, prevention, and effects of common grubs (digenetic trematodes) in freshwater fish. Tech Bull Series (Iowa State Univ) 2000;115:1–6. [Google Scholar]
  18. Lane RL, Morris JE (2010) Biology, prevention, and effects of common grubs (digenetic trematodes) in freshwater fish. NCRAC Technical Bulletins. 14
  19. Lane B, Spier T, Wiederholt J, Meagher S. Host specificity of a parasitic fluke: is Posthodiplostomum minimum a centrarchid-infecting generalist or specialist? J Parasitol. 2015;101(1):6–17. doi: 10.1645/14-584.1. [DOI] [PubMed] [Google Scholar]
  20. Lucky Z. Methods for the diagnosis of fish diseases. New Delhi: Amerind Publishing Co, PTV. LTD; 1977. [Google Scholar]
  21. Maghrabi O. Histopathological effects of some helminthic parasites on the liver of serranid fish. Res Rev J Zool Sci. 2017;5(1):36–43. [Google Scholar]
  22. Mansour MFA, Hassan SH, Khidr AA, Ghanem MA. General survey on certain helminth parasites infecting some Nile fishes at El-Mansoura, Egypt. Egypt J Aqual Biol Fish. 2003;7(4):423–446. doi: 10.21608/ejabf.2003.1801. [DOI] [Google Scholar]
  23. McAllister CT, Bursey CR, Robison HW, Connior MB, Trauth SE. New records of Helminth Parasites (Trematoda, Cestoda, Nematoda) from fishes in the arkansas and red river drainages, Oklahoma. Proc Okla Acad Sci. 2016;96:83–92. [Google Scholar]
  24. Meade TG, Bedinger CA., Jr Posthodiplostomum minimum in fishes of Madison County, eastern Texas. Southwest Nat. 1967;12:334–335. doi: 10.2307/3669123. [DOI] [Google Scholar]
  25. Mitchell AJ, Smith CE, Hoffman GL. Pathogenicity and histopathology of an unusually intense infection of white grubs (Posthodiplostomum m. minimum) in the fathead minnow (Pimephales promelas) J Wildl Dis. 1982;18(1):51–57. doi: 10.7589/0090-3558-18.1.51. [DOI] [PubMed] [Google Scholar]
  26. Mladineo I. Histopathology of five species of Didymocystis spp. (Digenea: Didymozoidae) in cage-reared Atlantic blue fin tuna (Thunnus thynnus thynnus) Vet Res Commun. 2006;30(5):475–484. doi: 10.1007/s11259-006-3207-6. [DOI] [PubMed] [Google Scholar]
  27. Nguyen TC, Li YC, Makouloutou P, Jimenez LA, Sato H. Posthodiplostomum sp. Metacercariae in the trunk muscle of the northern snakeheads (Channa argus) from the Fushinogawa River, Yamaguchi, Japan. J Vet Med Sci. 2012;74(10):1367–1372. doi: 10.1292/jvms.12-0025. [DOI] [PubMed] [Google Scholar]
  28. Noga EJ (2010) Fish diseases, diagnosis and treatment. 2nd edn. Iwa State University, Press, Ames
  29. Pauly D, Froese R (2007) (eds) Bagrus bajad. In: FishBase. Aug 2007 version
  30. Rabaldo RB, Monserrat J, Cousin JCB, Bianchini A. Effects of metacercariae (Digenea: Microphallidae) on the hepatopancreas of Chasmagnathus granulata (Decapoda: Grapsidae) Dis Aquat Org. 1999;37:153–157. doi: 10.3354/dao037153. [DOI] [Google Scholar]
  31. Ramadan RM, Saleh FS, Refaat ME. Suez Canal. Vet Med J. 2002;5:657–667. [Google Scholar]
  32. Ramos, Fonseca P, Branco I, Alexandre-Pires S, Graça (2012) Visceral infection of pumpkinseed sunfish (Lepomis gibbosus) with Posthodiplostomum minimum centrarchi – ultrastructural study. Bulgarian Journal of Veterinary Medicine 15(Suppl 1)
  33. Reddy BL, Benarjee G. Histopathology of intestine of trematode helminth infected fish. Int J Curr Microbiol App Sci. 2014;3(2):330–334. [Google Scholar]
  34. Ritossa L, Flores V, Viozzi G. Life-cycle stages of a Posthodiplostomum species (Digenea: Diplostomidae) from Patagonia, Argentina. J. Parasitol. 2013;99(5):777–780. doi: 10.1645/12-170.1. [DOI] [PubMed] [Google Scholar]
  35. Rossiter W, Davidson HM. Extrinsic and intrinsic predictors of variation in infection by Posthodiplostomum minimum MacCallum 1921 (Trematoda) in Sunfishes (Lepomis Rafinesque 1819) from Eastern Ohio. J Parasitol. 2018;104(3):202–209. doi: 10.1645/17-131. [DOI] [PubMed] [Google Scholar]
  36. Saleh RS, Abou-Eisha AM, Fadel HM, Helmy YH (2009) Occurrence of encysted metacercariae of some zoonotic trematodes in freshwater fishes and their public health significance in Port Said Province. Abbassa International Journal For Aquaculture, Special Issue for Global Fisheries & aquaculture Research Conference, Cairo International Convention Center, 24–26 October 2009, pp 341–351
  37. Schaaf CJ, Kelson SJ, Nusslé SC, Carlson SM. Black spot infection in juvenile steelhead trout increases with stream temperature in northern California. Environ Biol Fish. 2017 [Google Scholar]
  38. Shareef PAA, Abidi SMA. Studies on the epidemiology and histopathology of Euclinostomum heterostomum (Trematoda; Digenea) infection in Channa punctata from North India. Arch Pol Fish. 2015;23:133–140. doi: 10.1515/aopf-2015-0015. [DOI] [Google Scholar]
  39. Spall RD, Summerfelt RC (1970) Life cycle of the white grub, Posthodiplostomum minimum (MacCallum 1921: Trematoda, Diplostomatidae) and observations on host-parasite relationships of the metacercariae in fish. In: Snieszko SF (ed) A symposium on the diseases of fish and the shellfishes, pp 218–230. Bethesda, Maryland: American Fisheries Society. Special Publication 5 [Google Scholar]
  40. SPSS (2007) SPSS for Windows, version 16.0. Release 16.0.0. Chicago, IL
  41. Woo PTK (1995) Fish diseases and disorders. Volume I: protozoan and metazoan infections. CAB International, Wallingford, Oxon, UK
  42. Woodland J (2006) National Wild Fish Health Survey—Laboratory Procedures Manual. 3.1 Edition. U.S. Fish and Wildlife Service, Pinetop, AZ
  43. Zhang L, Vanderhorst K, Kyser K, Campbell L. Diet assimilation trends and host-parasite relationships in two species of sunfish (Lepomis) revealed by stable isotope analyses of multiple tissues. Parasitol Res. 2018 doi: 10.1007/s00436-018-5781-2. [DOI] [PubMed] [Google Scholar]

Articles from Journal of Parasitic Diseases: Official Organ of the Indian Society for Parasitology are provided here courtesy of Springer

RESOURCES