Internal disorders

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In contrast to those of farmed fish, internal disorders of ornamental fish have long been overlooked. Much of the early literature was written with an emphasis on identification of external diseases and occasional speculation about internal disorders. This chapter looks at anatomy, investigations, systemic approach, oral lesions, abnormal body shape, diseases of the vent and emaciation.

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Figure 16.1 The internal anatomy of a carp. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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Figure 16.2 Many fine peritoneal adhesions are found in normal koi and other carp.
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Figure 16.3 Severe ‘mouth rot’ due to bacterial infection in a goldfish. There is extensive necrosis of the soft tissues and exposure of the facial bones.
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Figure 16.4 A papilloma on the lip of a 3-year-old carp that was kept in an indoor aquarium. Most of the tumour was surgically removed but localized epidermal hyperplasia remained around the mouth.
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Figure 16.5 A large granulomatous mass (arrowed) in the pharynx of a porcupine pufferfish. The lesion also contained liquid pus and was thought to be due to penetration by prawn exoskeleton in the diet.
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Figure 16.6 Dislocation of the bones on the left side of the mouth in this adult koi caused partial obstruction and poor closure. The fish had difficulty eating a pellet diet and had laboured respiration. The cause was unknown.
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Figure 16.7 A 14-year-old goldfish that had a large tumour on its dorsal surface for 3 years. Histological examination identified this deeply invasive mass as a melanoma.
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Figure 16.8 An adult koi with a severe spinal deformity that was thought to be congenital in origin. There is also a large tumour causing distension of the posterior abdomen and displacement of the swim-bladder.
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Figure 16.9 A lionfish with a fractured spine. The injury is thought to have developed following an electric shock from a faulty water heater. A dorsoventral radiograph revealed fracture and displacement of the vertebral column. The injury produced a marked scoliosis, debilitating the fish to a degree where euthanasia was required. (© National Aquarium in Baltimore.)
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Figure 16.10 Vertebral fracture (arrowed) in a young orfe following bath treatment with an overdose of a proprietary medicine containing formalin. There is lateral deviation and haemorrhage at the fracture site.
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Figure 16.11 An adult koi with a massive gonadal tumour that accounted for one-third of its bodyweight.
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Figure 16.12 A fancy goldfish with abdominal swelling due to abnormal fluid collection in the swim-bladder. A mixed infection of pseudomonads and was isolated from the translucent yellow fluid.
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Figure 16.13 Abdominal swelling in a fancy goldfish that developed excessive positive buoyancy.
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Figure 16.14 Dorsoventral radiograph of the goldfish in Figure 16.13 , showing displacement of the posterior chamber of the swim-bladder and some unilateral abdominal swelling on the opposite side.
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Figure 16.15 Polycystic lesions in the kidneys of the goldfish in Figure 16.13 . The kidneys in severe cases may occupy up to 90% of the abdominal cavity.
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Figure 16.16 A young red-tailed catfish that swallowed an irregularly shaped piece of slate. The sharp anterior end penetrated the body wall but was removed successfully through the mouth while under anaesthesia.
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Figure 16.17 Severe abdominal swelling in this 12-year-old koi had been present for 1 year. Half of its bodyweight was due to intra-abdominal fluid and there were two cystic neoplastic masses.
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Figure 16.18 An adult koi with abdominal swelling for 6 months. In addition to a large liver tumour (large arrow), the bilobed sacks of the gonad (small arrows) were filled with translucent yellow fluid.
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Figure 16.19 Ruptured ovary in a common goldfish that had severe abdominal enlargement for several months. A large volume of ascitic fluid and degenerating eggs were present in the abdominal cavity.
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Figure 16.20 In freshwater fish, abnormal faeces may be long, white and stringy (left) or pale in colour (centre). Normal faeces from a goldfish are dark coloured and found in short fragments (right).
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Figure 16.21 Ova of with characteristic bipolar ‘plugs’, in a faecal sample from freshwater angelfish experiencing chronic mortalities in a breeding unit.
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Figure 16.22 are thin red nematodes found commonly in livebearers such as this platy. The parasites are only visible when protruding from the anus to release their live larvae.
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Figure 16.23 Juvenile koi with wasting of the dorsal musculature. Both fish are affected but the one on the left exhibits severe weight loss. Atrophic pancreatic cells thought to be a result of chronic malnutrition were found on histological examination. The other similarly affected fish in the group recovered on an improved diet.
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