Parasitic diseases

image of Parasitic diseases
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Many of the huge number of parasites recorded from fish are capable of inducing significant mortalities among captive and wild stocks. Accurate identification of parasites is important, in order that a build-up of parasite numbers can be prevented. This chapter describes protistan parasites, myxozoan parasites and metazoan parasites.

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Figure 21.2 An example of a sp. can be seen amongst the nucleated erythrocytes in this stained blood smear. (May-Grünwald–Giemsa stain.)
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Figure 21.3 Large numbers of parasites (arrowed) attached to the surface of the gill. (H&E stain.)
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Figure 21.4 observed by phase contrast. Note the elongate body and presence of flagella. (Wet mount preparation.)
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Figure 21.5 sp. The heart-shaped organism and its longitudinal striations are visible. (Wet mount preparation, DIC microscopy.)
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Figure 21.6 Example of sp. The radial denticles used in species differentiation can be seen clearly. (Wet mount preparation, DIC microscopy.)
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Figure 21.7 Three trophonts on the fin of a goldfish. Note the presence of a horseshoe-shaped nucleus in the trophont. Some monogeneans sp. are also present in this sample. (Wet mount preparation.)
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Figure 21.8 Typical amoebae (arrowed) present in loose association with the tips of the gill filaments. (H&E.)
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Figure 21.9 Squash preparation of in kidney tissue from a gudgeon. (Wet mount preparation, DIC microscopy.)
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Figure 21.10 Coccidia (arrowed) are present in the epithelial cells of the intestine in this histological section. (ZN stain.)
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Figure 21.11 A microsporean xenoma in a histological section of the gastrointestinal tract. Note the presence of numerous refractile spores within the xenoma. (H&E stain.)
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Figure 21.13 spores (arrowed) in the kidney tubules of carp. Compared with uninfected renal tubules, parasitized tubules are greatly dilated. (Giemsa stain.)
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Figure 21.14 Histological section of the kidney from a goldfish with kidney enlargement disease. Massive numbers of parasites are present within the lumen and hyperplastic epithelial cells of the renal tubules. (H&E stain.)
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Figure 21.15 Examples of myxozoan parasites. (a) ; (b) ; (c) ; (d) ; (e) .
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Figure 21.17 Example of sp. attached to the fin of a goldfish. The parasite is firmly attached by the opisthohaptor. The uterus contains a juvenile and is clearly visible in the middle of the body. (Wet mount preparation, DIC microscopy.)
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Figure 21.18 sp. removed from the skin of a marine fish. The round opisthohaptor, typical in capsalid monogeneans, is used to secure the parasite to the host. (Wet mount preparation.)
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Figure 21.19 Characteristic tetrahedral eggs with fine threads used for attachment to fish and other objects. (Wet mount preparation) (© W.H. Wildgoose.)
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Figure 21.20 , a polyopisthocotylean monogenean, isolated from the gills of trout. Unlike the adult forms, this immature specimen contains three pairs of clamps (arrowed), rather than four. Breakdown products of host blood can be seen as dark deposits at the periphery of the parasite. (Wet mount preparation.)
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Figure 21.21 Typical species-dependent life cycle of monogeneans, showing the two alternative pathways.
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Figure 21.22 A typical digenean. Note the presence of an apical (a) and a ventral (v) sucker (arrowed). (Wet mount preparation.)
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Figure 21.23 Simplified life cycle of digenean parasites.
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Figure 21.24 Photomicrograph of sp. in the lens of a fish. (Wet mount preparation.)
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Figure 21.25 Simplified life cycle of cestode parasites.
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Figure 21.26 Histological section through the intestine of a carp infected with a cestode. (H&E stain.)
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Figure 21.27 Head region of a nematode ( sp.) showing mouthpart detail (Wet mount preparation.)
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Figure 21.28 Simplified life cycle of nematode parasites.
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Figure 21.29 Proboscis of the acanthocephalan , showing numerous spines. (Wet mount preparation, DIC microscopy.)
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Figure 21.30 Simplified life cycle of acanthocephalan parasites.
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Figure 21.31 . The holdfast, or ‘anchor’, is normally buried under the skin of the host. The distal portion, showing two egg strings (arrowed), is normally the only part of the parasite that is visible externally. Scale in millimetres. (Wet mount preparation.)
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Figure 21.32 The branchiuran isolated from the skin of a carp. (Wet mount preparation.)
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Figure 21.33 Two examples of a gnathid isopod: (a) a juvenile stage (praniza), which is parasitic; (b) a large adult, which is not normally parasitic.
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