Background

The genus Gnathostoma (Nematoda) comprises 17 species, Nematodes of genus Gnathostoma are nematode parasites mostly found in the stomach wall of certain vertebrate hosts, specimens are zoonotic agents of wild animals, the larvae are also pathogenic in humans and certain animals (Daengsvang, 1981). When the infected copepods are ingested by various intermediate or paratenic hosts such as fishes, amphibians, reptiles, the larvae develop further to become advanced third-stage larvae (AL3) that infect the definitive hosts. Cyclopoid copepods play a crucial role in maintaining the life cycle of Gnathostoma. In Thailand, 4 species of cyclopoid copepods, Mesocyclops leuckarti, Eucyclops agilis, Cyclops Varicans, and Thermocyclops sp. were proven experimentally to be first intermediate hosts of M. aspericornis, the pan tropical freshwater cyclopoid copepod widely distributed in Asia, America and Africa (Van de Velde, 1984; Rocha and Botelho, 1998).

The Sillaginidae fish family are marine, many species inhabit estuarine environments fishes are grown to an average of about 20 cm and 100 g (Kuiter, 1993). All species occupy mostly sandy, muddy substrates, often using seagrass or reef as a home (Krishnayya, 1963).

The nematode fauna of the Iraqi marine waters is still poorly known, the reports on nematodes of marine fishes included those from Khor Abdullah (Bannai, 2002; Awad et al., 2003), Khor Al-Ummaia (Moravec and Ali, 2005; Ali, 2008; Al-Salim and Ali, 2010; Al-Salim and Ali, 2011; Al-Salim and Ali, 2012; Ali et al., 2012; Ali and Al-Salim, 2013; Moravec and Ali, 2013) and the coastal marine waters (Al-Ataby, 2012; Moravec et al., 2012; Jassim, 2013; Ghadam et al, 2017). More than 45 species are described. The aim of the present study is to identify gnathostomidae nematodes in Iraqi marine waters and the geographical distribution, the feeding habits, and stomach contents of their host's.

1 Materials and Methods

Seventy-five specimens of Sillago sihama and 6 specimens of Argyrops spinifer (Forsskål, 1775, King soldier bream) were collected from from Khor Abdullah, the Arabian Gulf (Figure 1) during the survey of nematode parasitic fauna in the year of 2017. After the biometric analysis, fish organs were removed, placed in a Petri dish with saline solution, and examined. The recovered helminths were fixed in AFA (93 parts 70% ethyl alcohol, 5 parts formaldehyde, and 2 parts glacial acetic acid). For morphological analysis, the nematodes were dehydrated in an ethanol series, clarified with lactophenol, placed on a microscope slide under a coverslip as a temporary mount, observed using a light microscope, and photographed using a Canon camera microscope with an imaging capture system. Measurements are shown in micrometers. Parasite identified according to Yamaguti (1961) and DA Silva Pinheiro et al. (2017), and Almeyda-Artigas (1991). For the study of food and feeding habits and their relationships with infections, fish stomachs were analyzed for their fullest and the stomach contents were discharged into Petri dishes and examined qualitatively and quantitatively. Food contents were grouped into 7 categories, i.e. Teleosts, Shrimp, Echinoderms, Crustaceans, Annelids, Miscellaneous, Nematodes. All the points gained by each food item were summed up and scaled to give a percentage composition of food of all fish examined.

2 Results and Discussion

1-Taxonomic summary

Family: Gnathostomatoidea Railliet, 1895

Genus: Gnathostoma Owen, 1836

A-Gnathostoma binucleatum (Almeyda-Artigas, 1991) (Figure 2A)

Host: Argyrops spinifer (Forsskål, 1775, King soldier bream)

Infection site: Intestinal

Location: Khor Abdullah, Iraqi marine coastal water, Arabian Gulf (29°58,33N, 48°28,20E)

Prevalence: 8.77% (5 of 57 hosts infected)

Description based on 3 third-stage larvae (L3) nematode, medium-sized nematodes, body unarmed, cylindrical, 52 mm long by 0.6 mm wide at greatest width. Cephalic bulb 422 long by 646 wide, six discontinuous circles of spines containing I: 31-35, II: 34-39, III: 38-40, IV: 34-37, V: 30-35, and VI: 30-33 spines, respectively, increasing in size posteriorly (Figure 1). Nerve ring 2 mm at level of cephalic bulb, from anterior end. Esophagus divided near midpoint into anterior muscular and posterior glandular regions 6%, 1.6 mm long by 283 widths; Tail conical, with blunt unornamented tip.

2-Gnathostoma sp., (Figure 2B)

Host: Sillago sihama (Forsskal, 1775, Sillaginidae)

Infection site: Intestinal

Location: Khor Abdullah, Iraqi marine coastal water, Arabian Gulf (29°58,33N, 48°28,20E)

Prevalence: 8.77% (5 of 57 hosts infected)

Of the 57 specimens of Sillago sihama that were collected, one was parasitized by third-stage larvae (L3) a of a nematode encysted in the intestinal serosa; this larva presented characteristics of species of the genus Gnathostoma. Gnathostoma sp. (Third-stage larvae) (Figure 2B).

Description based on 5 third-stage larvae (L3) nematode. Medium-sized nematodes, body cylindrical, measuring 11 mm × 300 widths. Circular oral cavity surrounded by two lateral lips with paired papillae. Cephalic bulb 313 (270 × 320, six discontinuous circles of spines containing I: 30, II: 34, III: 38, IV: 35, V: 35 and VI: 32 spines, respectively. Nerve ring located at the level of cephalic bulb, from the anterior end. Muscular esophagus 2.60 mm, occupying 25% of body length. Two pairs of transparent contractile sacs in the anterior half of the body.

2.1 Clinic-pathology in the Sillago sihama (Forsskal, 1775, Sillaginidae)

The clinical pathology studies of the larvae encysted in the skeletal muscle of fishes show histological lesions from hyperplasia of fibrous connective tissue around the worm, with the infiltration tissue of macrophages in the interstitial infection. The inflammatory response in muscle tissue included granulomatous lesions.

2.2 The relationship between fish length, food items and infection Sillago sihama (Forsskal, 1775, Sillaginidae)

Fifty-seven specimens of Sillago sihama were examined. The length of infected adults was 15-25 cm long. The major food items found in the stomach are shown in Table 1. The largest groups of food items observed were animal parts, i.e. appendages, Chela, parts of the carapace of crustaceans during all months. Juveniles appear to feed mainly on crustaceans and the adults on crustaceans, molluscs, polychaetes, echinoderms teleosts, among other items. A few nematodes were also observed in a stomach of a few fishes (Table 1). The occurrence of various food items was distinctly different according to the fish size. However, it was clear that the juveniles feed mainly on crustaceans and the adults mainly feed on crustaceans, molluscs, polychaetes, echinoderms teleosts, and others (Figure 3).

The monthly occurrence of different food items in the stomach of S. sihama shows that a high percentage of occurrence of a miscellaneous group of food was recorded in all months of the years with the highest percentage in April and May (Table 1). While crustaceans were the second ranking food items, the highest percentage occurred during five months of the year. Shrimp was detected in all months and the summer season showed the height percentage, Animals (eggs, scales, insect and crustacean appendages, etc.) were detected in all month of the years with varying percentages.

The morphological characterizations of structure the cephalic bulb are the main important characteristics used for the differentiation of members of family Gnathostomatidae (Miyazaki, 1960). Genus Gnathostoma (Owen, 1836) are comprising of 17 species: G. spinigerum Owen, 1836; G. gracile Diesing, 1839; G. socialis Leidy, 1858; G. hispidum Fedtschenko, 1872; G. turgidum Stossich, 1902; G. doloresi Tubangui, 1925; G. americanum Travassos, 1925; G. didelphis Chandler, 1932; G. procyonis Chandler, 1932; G. nipponicum Yamaguti, 1941; G. minutum Schuurmans-Stekhoven, 1943; G. brasiliense Ruiz, 1952; G. miyazakii Anderson, 1964; G. vietnamicum Le-Van, 1965; G. malaysiae Miyazaki & Dunn, 1965; G. binucleatum Almeyda-Artigas, 1991; and G. lamothei Bertoni-Ruiz et al., 2005. Miyazaki (1954) suggested that the number, shape, and size of the spines; of the shape of the cephalic bulb; and the location of the cephalic papillae and excretory pore are the main specific characteristics that distinguish different species of the genus Gnathostoma.

The nematodes founded encysted in the intestinal serosa in this study have characteristics of species of genus Gnathostoma, similar with Gnathostoma binucleatum are described by Almeyda-Artigas (1991) by including the presence of a cephalic bulb armed with spines, a circular oral cavity surrounded by two lateral lips with a pair of papillae on each. This study has designated these larvae, as being third-stage larvae because this is usually the stage found in fish. However, third-stage larvae usually are smaller than 10 mm in length; the ones reported herein are 10-14 mm in length, a size more typical of fourth-stage larvae. There are many reports of larvae of Gnathostoma naturally parasitizing fish in Iraqi marine water of Arabian Gulf fishes and this study consider Gnathostoma binucleatum as a new record in Arabian gulf fishes. The present study is the third report of Gnathostoma and the fishes S. Sihama and Argyrops spinifer (Forsskål, 1775, King soldier bream) as a new intermediate host that participate in the life cycle of members of this genus.

Histopathology study caused by adult worms of genus Gnathostoma has been down in many regions of the world for several host species, in the dogs (Nayar et al., 1978), cats (Beveridge et al., 1978), weasels (Ashizawa et al., 1979), and pigs and boars (Chen et al., 2001). Pathogenic changes by advanced third stage larvae of Gnathostoma have only been studied in fish-eating birds (García-Márquez et al., 2001). Host-parasite interaction determines the type of inflammatory reaction; the characterization of the different levels of this response, described by Vazquez-Nunez et al. (2004), the useful guide to analyze the lesions caused by parasites as Gnathostoma to provide us the basic understanding principles of the pathogenesis and pathology of gnathostomiasis.

Analysis structure of stomach contents of S. sihama in our study showed the presence of 4 groups of food items: Molluscs, Crustaceans, Polychaetes and Miscellaneousblue. The study of Shamsan and Ansari (2008) pointed out that the crustaceans are the most important food item in the Stomach of S. sihama in Zuari Estuary of India. Norris (2004) studies from the waters of Thailand, Philippines and Australia have shown that polychaetes, varieties of crustaceans, molluscs and to a lesser extent echinoderm and fish are the predominant prey items of the family. In this study show that the copepods and crabs were dominant in spring and summer. Feeding activity of the S. sihama in the Iraqi marine water fish distribution was strongly reduced during the summer months. The maximum number of empty stomachs was recorded during the summer. The abdominal cavity is fully occupied by the ripe gonads and so stomachs were always empty during the summer (Kariman et al., 2009). Commonly taken crustaceans included decapods, copepods and isopods, while the predominant molluscs taken were various species of bivalves, especially the unprotected siphon filters that protrude from the shells. These results suggest that the summer is not the time for infection of parasites.

3 Conclusion

More study needed to recognize on the larval stage parasite infection and their clinical pathology to provide a basic understanding of the general principles of the pathogenesis and pathology of gnathostomiasis, and the relationship between fish length, food items and infection.

Acknowledgements

This project was supported by the Department of Marine Vertebrate, Marine Science Center, University of Basrah. Iraq. Am thankful to Omar Amin Institute of Parasitic of Diseases, Scottsdale, USA for his support of the paper corrected and publishing.

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