Unpredictable Repeated Stress in Rainbow Trout (Oncorhynchus mykiss) Shifted the Immune Response against a Fish Parasite
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Farmed fish are regularly subjected to various stressors due to farming practices, and their effect in the context of a disease outbreak is uncertain. This research evaluated the effects of unpredictable repeated stress in rainbow trout challenged with the ciliate Ichthyophthirius multifiliis, known to cause white spot disease in freshwater fish. Before and after the pathogen exposure, fish were handled with a random rotation of three procedures. At 7 days post-infection (dpi), the parasite burden was evaluated in fish and in the tank’s water, and the local and systemic immune responses were investigated in the gill and spleen, respectively. The fish mortality was recorded until 12 dpi, when all the fish from the infected groups died. There was no statistical difference in parasite burden (fish and tank’s water) and infection severity between the two infected fish groups. The immune gene expression analysis suggested a differential immune response between the gill and the spleen. In gills, a T helper cell type 2 immune response was initiated, whereas in spleen, a T helper cell type 1 immune response was observed. The stress has induced mainly upregulations of immune genes in the gill (cat-1, hep, il-10) and downregulations in the spleen (il-2, il-4/13a, il-8). Our results suggested that the unpredictable repeated stress protocol employed did not impair the fish immune system.Keywords:
Ichthyophthirius multifiliis
Four specimens of this parasite were collected from the gills of about two dozen Dussumieria acuta , a fish which is of market value in Madras. Of the four specimens, two were female and two were male; no two were found in the same fish. Both the males were 1·5 mm. long, while the two females measured 2·6 and 2·5 mm. respectively.
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The dependence of immunological reactions of fishes infected with Ichthyophthirius multifiliis infusoria was elucidated. The invasion of the parasite results in the activation of the immune system, increased phagocytosis and a growth of the activity of oxydase enzymes. With the increased number and sizes of parasites a decrease of the above parameters below the control values is observed. Changes of the immunological values are most dynamic at high (20-25 degrees) and they are slower at low (10 degrees) temperatures.
Ichthyophthirius multifiliis
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Ichthyophthirius multifiliis Fouquet, 1876 usually infected the skin, gills, fins and barbels of largemouth bronze gudgeon (Coreius guichenoti (Sauvage Dabry), 1874). The parasitization on gills was classified into three degrees:(1) slight parasitization, i. e., I. Multifiliis parasitized on epithelia and gills filaments didn't fuse together; (2) heavier parasitization, i. e. , gills filaments fused together and the filament configuration could be discerned; and (3) heaviest parasitization, i. e. , the gills filaments were seriously damaged, and their configuration could hardly be distinguished. The parasite caused hyperplasia of the host epidermis, and was surrounded by the hyperplastic tissues. When the mature parasite broke walls consisting of the hyperplastic tissues, it resulted in lesions of the parasitic sites and secondary infection of bacteria. Therefore, some infected sites were usually congestive and ulcerated. Infected barbels were ulcerated and sometimes gradually disappeared. Infected fins were also ulcerated and their rays were extruded or distorted by the trophonts of the parasite.
Ichthyophthirius multifiliis
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The protozoan parasite Ichthyophthirius multifiliis is an economically important parasite for the aquaculture- and ornamental fish industry. The parasite is abundant worldwide and infects the skin, gills and fins of freshwater fish species. For approximately the last fifty years the innate and protective immune mechanisms induced by I. multifiliis have been in focus in different fish hosts. By utilizing transgenic zebrafish, new tools to investigate this have emerged. The aim of this study was therefore to elucidate early immune responses in zebrafish larvae by using gene expression and in vivo imaging of neutrophil and macrophage behavior during infection. For the first time, zebrafish larvae were infected with the parasite and infection dynamics, parasite size and host-parasite interactions were investigated. Results showed that the larvae responded with mild inflammation and that the 12 compared to 5 days post fertilization larvae were significantly less susceptible. It was furthermore observed that neutrophils and macrophages were attracted to the parasites and that neutrophils reacted with neutrophil extracellular traps (NETs) when fighting the parasite. The parasite was rotating vigorously, presumably to impede the neutrophils and macrophages from attaching to it but on rare occasions, neutrophils and macrophages were able to kill the parasite. Based on these observations, we concluded that the parasite uses the rotation as an immune evasive strategy and that the zebrafish larvae respond with high activity from neutrophils and macrophages locally but systemically only with mild inflammation.
Ichthyophthirius multifiliis
Protozoan parasite
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Vacuolization
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This study established ex vivo conditions suitable for studying early trophont development in excised tissues of channel catfish Ictalurus punctatus within the first 48 h. Infective theronts of Ichthyophthirius multifiliis were added to freshly excised channel catfish fin, gill, and skin and established fin cells (BF-2) of bluegill Lepomis macrochirus. The early development of trophonts, including growth, rotation speed, attachment, and survival (%), was studied in different tissues and at different times. In all, 86–92% of the theronts attached to fish tissues in an enter, leave, and reenter pattern within the first 10 min. Theront attachment was more than 88% in fins, gills, and skin 1 h post exposure (PE). Attachment and shape transformation of theronts were not observed on BF-2 cells. Trophonts grew to a size of 30.0 ± 3.1 μm in diameter 4 h PE in the gills, an increase of 9.6%/h. The size increase of trophonts was 1.2%/h in the gill between 4 and 8 h. Trophonts grew slowly and increased in diameter 0.5%/h from 8 to 48 h after addition to the gills. The mean volumes of trophonts at 1, 24, and 48 h PE in gills were 1,072.6 ± 3,131.6, 20,373.6 ± 8,357.4, and 28,102.3 ± 4,740.0 μm3, respectively. No difference in trophont rotation speed was found in different tissues between 1 and 24 h PE. At 48 h, the rotation speed of trophonts was significantly slower (P < 0.01); the average speed was 819.3 ± 195.7 μm/min. Most trophonts were alive 8 h PE; survival was higher than 97%. The mean survival was 67.8% at 24 h and 8.4% at 48 h PE in all tissues. The viability of excised tissues without theronts was considerably higher than that in tissues with theronts after 48–72 h in culture.
Ichthyophthirius multifiliis
Lepomis macrochirus
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Ichthyophthirius multifiliis
Fresh water fish
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Ichthyophthirius multifiliis
Danio
Protozoan parasite
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Fresh water fish
Bioconcentration
Freshwater ecosystem
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Histopathological changes in gills of a native fish Capoeta aculeata, naturally-infected with parasites were studied. The specimens (15.5 to 22.8 cm) were collected from Choghakhor lagoon in West Iran. 35 (11%) of the total 318 studied fishes were infected with gill parasites. Overall, six protozoan and metazoan parasite species were collected from fishes including Ichthyophthirius multifiliis, Trichodina sp., Myxobolus musayevi, Dactylogyrus extensus, Gyrodactylus sp. and Copepod stage of Lerneae cyprinacea . The gills of infected fish were fixed and processed for routine histological investigations. Histopathological changes and tissue reactions included hyperplasia, congestion and mucous cell proliferation of the gill epithelium and damaged primary and secondary lamellae. Histopathological changes induced by the parasites adversely affected the proper functioning of the gills of the host fish. Key words: Gill parasites, histopathology, Capoeta aculeata, Choghakhor lagoon.
Trichodina
Ichthyophthirius multifiliis
Histopathology
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