Comparative study of Helminth community and their effect on Xenentodon cancila (Hamilton, 1822) and Polynemus paradiseus (Linnaeus, 1758)

Abstract

In the present study, a total of 321 Xenentodon cancila and 321 Polynemus paradiseus were examined during the period of January 2017 to December 2018 (both from Swarighat, Dhaka) for the investigation of parasite infestation, DNA barcoding of parasites, proximate composition and pathological effects on the hosts. A total of 9 species of parasites were collected and identified from X. cancila, of which two were trematodes (Bolbocephalus sp, Isoparorchis hypselobagri); four nematodes (Metaquimperia bagari, L 3 larva of Gnathostoma spinigerum, Camallanus ophiocephali, Porrecaecum trichuri.) and three acanthocephalans (Neoechinorhynchus prolixum, Acanthocentis nigeriensis, Pallisentis ophiocephali). From Polynemus paradiseus, a total of 10 species of parasites were recovered and identified. Among them, four were trematodes (Prosogonotrema bilabiatum, Uterovesiculurus hamati, Thaparotrema vittalani, Hypohepaticola callionymi); two cestodes (Nybelinia lingualis, Parachristianella trygonis); two nematodes (L 4 larva of Dujardinascaris sp., Metaquimperia bagarii) and two acanthocephalans (Neorhadinorhynchus aspinosum, Pallisentis ophiocephali). Acanthocephalan parasites showed the highest infestation rate (57%) whereas no Cestoda was found in X. cancila. Trematode parasites showed the highest prevalence (68%) in P. paradiseus. Among the total helminth parasites recovered, the most numerically dominant and highly prevalent acanthocephala was Pallisentis ophiocephali (23% with mean intensity 1.14 in X. cancila and 4% with mean intensity 1.17 in P. paradiseus) and trematode was Prosogonotrema bilabiatum (23% with mean intensity 1.03) in P. paradiseus.

The prevalence of infestation of parasites was 60% in X. cancila (192 specimens) with mean intensity 1.14 per infested fish while in P. paradiseus, 49% was infested (158 specimens) with mean intensity 1.09. Regarding the organal distribution, most of the parasites were found to favour the intestine of both host fish. The prevalence of infestation in X. cancila was observed higher during winter while in P. paradiseus, it was higher during rainy season. The maximum intensity of parasites of X. cancila was recorded during rainy season and in P. paradiseus, it was recorded during summer.

The effects of modifying factors such as sex, season, length, climate and diet of the hosts on the abundance of parasites were also studied. Among the main food items, small fishes comprised the greatest proportion (37%) in X. cancila, whereas, it comprised only 19% in P. paradiseus; the crustacean food item was 28% in X. cancila while in P. paradiseus, it was 31%; the mollusks comprised the highest proportion (35%) in P. paradiseus, whereas, in X. cancila, it comprised of 5%. X. cancila and P. paradiseus also consumed aquatic insects, tadpoles, annelids as additional food. Presence of large variety of small fishes, crustacean and other invertebrates in the stomach and intestine indicated their possibility as “carrier host” of these parasites in both host fish.

Helminth parasites especially immature stages caused tissue damages through formation of tunnels by lysing and ingestion of tissues. This is followed by moisture accumulation, tissue destruction, hemorrhage and massive melanization in different parts and organs of the hosts. Infected liver and kidney showed incipient vacuolation and massive melanization. Massive pigmentation was also noted in viscera of X. cancila due to the infection of juvenile Isoparorchis hypselobagri. The present observation on biochemical analysis presented small variation in nutrient contents between X. cancila and P. paradiseus. Protein, fat, and ash level were higher in noninfected X. cancila and P. paradiseus than those of infected.

DNA barcoding is a widely spread technique for species identification. An attempt has

been

made to molecular identification of acanthocephalan parasites based on mitochondrial cytochrome oxidase I (COI) gene as marker. In this study, one acanthocephalan species (Pallisentis ophiocephali) was identified. A total of three sequences of one species was generated. The species was identified by adopting DNA barcoding of mitochondrial cytochrome c oxidase subunit I (COI) gene. Genetic divergence was observed 0% within species and 22% between species. Phylogenetic tree was established where individuals belonging to the same species were grouped under same clade. The species Pallisentis ophiocephali has been newly recorded. The study showed the efficiency in identifying acanthocephalan species which might work as a referral study for molecular identification of parasites in Bangladesh.