Environmental disorders

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Deviant environmental factors are often the trigger to a cascade of events leading to unhealthy fish. In many cases, these result from poor husbandry and can be divided into water quality disorders and exogenous factors. This chapter explores water quality disorders, nitrogenous compounds, salinity, dissolved gases and exogenous factors.

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Figure 25.1 Heavy algal bloom in an outdoor pond. The effects of photosynthesis produced pH 10.5 at midday, resulting in corneal oedema, skin lesions and mortality. (© W.H. Wildgoose.)
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Figure 25.2 Excess detritus in a single chamber filter unit used on a garden pond. The brown sediment was only noticed after the water was drained out. This thick sediment blocked the filter medium, preventing any biological activity and causing poor water quality. (Courtesy of W.H. Wildgoose.)
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Figure 25.3 The capillary tube at the top is from a catfish suffering from methaemoglobinaemia. The distinctive brown coloration is clearly visible when compared with the other tube, which contains blood from a normal fish. (Courtesy of Lester Khoo, VMD.)
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Figure 25.5 Fish crowding around a water inlet in a pond with poor aeration. The decomposition of dead algae (brown sediment) in the pond further depletes dissolved oxygen levels. (© W.H. Wildgoose.)
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Figure 25.6 The overgrowth of surface plants reduces the surface area for gas exchange. This causes environmental hypoxia and prevents the growth of aquatic algae. (© W.H. Wildgoose.)
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Figure 25.7 ‘Gas bubble disease’ affecting the eye of a mummichog. Gas bubbles are visible in the dorsal periorbital tissue. (© National Aquarium in Baltimore.)
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Figure 25.8 Dorsoventral radiograph of a koi following lightning strike. The fish exhibited a stiff swimming motion and inability to fully flex the caudal peduncle, due to the severe fracture and dislocation of the vertebral column. (Courtesy of Alex Barlow.)
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Figure 25.9 Sunburn on the dorsum of a koi in a shallow outdoor pond. The generalized inflammation and petechiation affected only the white areas on the dorsal surfaces. (© W.H. Wildgoose.)
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