Parasite diversity and their effects on histological and biochemical components of Wallago attu (Bloch-Schneider, 1801) and Rita rita (Hamilton-Buchanan, 1822)

Abstract

In the present investigation, a total of 250 W. attu and 350 R. rita were examined during January 2011 to December 2012 (both from Swarighat, Dhaka) for the investigations on parasite infestation, proximate composition and pathological effects on the hosts. A total of 11 species of parasites collected and identified from W. attu, one ecto-parasite (Argulus foliaceus) and 10 endo-parasites of which three were trematodes (Isoparorchis hypselobagri, Macrolecithus gotoi, Magnacetabulum trachuri); two nematodes (Contracaecum L3 larva, Cosmoxynemoids aguirrei); one cestode (Polyoncobothrium polypteri) and four acanthocephalas (Echinorhynchus kushiroense, Pallisentis ophiocephali, Acanthocephalus aculeatus, Pallisentis umbellatus). From R. rita, a total of 9 species of parasites recovered and identified, among them, one ecto-parasite (Lernaea cyprinacea) and 8 endo-parasites of which four trematodes (Notoporus leiognathi, Saccacoelium obesum, Sterrhurus musculus, Clinostomum piscidium); one nematode (Ascaroid larva) and three acanthocephalas (Cavisoma magnum, Corynosoma alaskense, Corynosoma strumosum). The parasite community in both W. attu and R. rita was dominated by trematodes and acanthocephalans comprising 33.31% and 47.9% of the total number of parasites from W. attu and 59.12% and 31.99% of those in R. rita. Among the total helminth parasites recovered, the most numerically dominant acanthocephalan was Pallisentis ophiocephali (14.58%) in W. attu and trematode Notoporus leiognathi (18.26%) in R. rita. The prevalence of infestation of ecto-parasite was 23.6% in W. attu (59 specimens) and mean intensity of parasite was 3.11 ± 1.47 per infested fish while in R. rita, 24.8% were infected (87 specimens) with a mean intensity of parasites was 3.34 ± 1.62. The prevalence of infestation of endo-parasites was 34.4% in W. attu (86 specimens) and mean intensity of parasites was 1.66 ± 0.24 per infested fish while in R. rita, 64.57% were infected (226 specimens) with a mean intensity of parasites was 2.64 ± 1.12. Regarding the organal distribution, most of the parasites were found to favour the intestine of the fishes, except Isoparorchis hypselobagri was harboured the swim bladder. The prevalence of infestation in W. attu was observed higher during winter season while in R. rita, the prevalence of infestation was higher in rainy season. The maximum intensity of parasites of W. attu was recorded in winter and in R. rita, that was found in summer. The effects of modifying factors such as sex, season, length, climatic factors and diet of the hosts on the abundance of parasites were also studied. Among the main food items, small fishes comprised the greatest proportion (27.2%) in W. attu, whereas, in R. rita, it was 18.3%; the crustacean food item was 17.6% in W. attu while in R. rita, it was 4.8%. W. attu and R. rita also consumed aquatic insects, mollusks as additional food. Presence of large variety of small fishes and other invertebrates in the stomach indicated their possibility as “carrier host” of these parasites in both the hosts. Juvenile Isoparorchis hypselobagri caused massive tissue damages resulting in erosions and formation of tunnels in the musculature, accumulation of moisture, connective tissue dislocation, massive melanization and mixed inflammatory responses in W. attu. The infected liver showed incipient vacuolation, accumulation of melanin macrophage centers and hemopoietic tissue degeneration. Massive pigmentation was also noted in swim bladder of W. attu due to the infection of juvenile Isoparorchis hypselobagri. The present observation on biochemical analysis presented small variation in nutrient contents between W. attu and R. rita. Protein, fat, moisture, carbohydrate and ash level were higher in non-infected W. attu and R. rita than those of infected.