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Created page with "==Introduction== The nitrogenous cycle converts toxic nitrogenous waste into relatively non-toxic compounds and is carried out by a mixed population of bacteria present in the bi..."
==Introduction==
The nitrogenous cycle converts toxic nitrogenous waste into relatively non-toxic compounds and is carried out by a mixed population of bacteria present in the biological filter and in surface biofilms. Ammonia is oxidised first to nitrite then to nitrate.
Both ammonia and '''nitrites''' are very toxic to fish, nitrate is less toxic but should not be left to accumulate to high levels.
Nitrite is transported across the gills where it enters the bloodstream and oxidises '''haemaglobin to methaemaglobin'''. This leads to tissue hypoxia.
Nitrate toxicity is particularly a problem in '''newly-established recirculating systems''', in which insufficient numbers of bacteria are present in the biological filter. This can also be a problem when the biological filters have been damaged by the interruption of water supply, '''excessive cleaning''' or '''antibacterial administration'''.
Species susceptibility to nitrate is '''variable''' and is linked to '''chloride uptake''' by the gills. Nitrite competes for chloride absorption, therefore fish with a high chloride uptake such as the rainbow trout, the perch, the pike and the catfish are more susceptible to nitrite. In contrast, the largemouth and smallmouth bass, bluegill and green sunfish are resistant to high concentrations of nitrite.
==Clinical Signs==
Fish with nitrite toxicity will present with '''tan to brown-coloured gills''' and show signs of '''hypoxia''' such as gathering at the water inlet or surface.
Changes in oxygen affinity and blood pH increase the movement of oxygen to the swim bladder. This can lead to '''buoyancy problems'''.
==Diagnosis==
Diagnosis relies on the '''measurement of nitrite levels''' in the system or tank water, and some gross evidence of methaemaglobinaemia.
Toxicity levels vary between species of fish, but it is preferable to keep levels as low as possible in all cases.
==Treatment and Prevention==
Nitrite is much less toxic when '''chloride''' is present, possibly because chloride inhibits nitrate absorption across the gills.
'''Sodium chloride''' is the most available and cheapest source of chloride.
Haemaglobin levels should return to normal within 12-24 hours. If severe anaemia is present '''recovery may take weeks'''.
The original cause of the nitrate toxicity should be resolved and levels of nitrate in the water can be reduced through '''water changes, biological filtration and decreased feeding'''.
Prevention involves ensuring an '''adequate levels of chloride''' in the water at all times. Most waters already have enough chloride and prophylactic treatment is unnecessary.
{{Learning
|flashcards = [[Ornamental Fish Q&A 13]]
}}
==References==
Noga, E. (2010) '''Fish Diseases: diagnosis and treatment''' ''John Wiley and Sons''
Gupta, R. (2007) '''Veterinary toxicology: basic and clinical principles''' ''Academic Press''
Dietrich, H. W. (2009) '''Essential Zebrafish Methods: Genetics and Genomics''' ''Academic Press''
[[Category:To Do - Helen]]
[[Category:To Do - Review]]
The nitrogenous cycle converts toxic nitrogenous waste into relatively non-toxic compounds and is carried out by a mixed population of bacteria present in the biological filter and in surface biofilms. Ammonia is oxidised first to nitrite then to nitrate.
Both ammonia and '''nitrites''' are very toxic to fish, nitrate is less toxic but should not be left to accumulate to high levels.
Nitrite is transported across the gills where it enters the bloodstream and oxidises '''haemaglobin to methaemaglobin'''. This leads to tissue hypoxia.
Nitrate toxicity is particularly a problem in '''newly-established recirculating systems''', in which insufficient numbers of bacteria are present in the biological filter. This can also be a problem when the biological filters have been damaged by the interruption of water supply, '''excessive cleaning''' or '''antibacterial administration'''.
Species susceptibility to nitrate is '''variable''' and is linked to '''chloride uptake''' by the gills. Nitrite competes for chloride absorption, therefore fish with a high chloride uptake such as the rainbow trout, the perch, the pike and the catfish are more susceptible to nitrite. In contrast, the largemouth and smallmouth bass, bluegill and green sunfish are resistant to high concentrations of nitrite.
==Clinical Signs==
Fish with nitrite toxicity will present with '''tan to brown-coloured gills''' and show signs of '''hypoxia''' such as gathering at the water inlet or surface.
Changes in oxygen affinity and blood pH increase the movement of oxygen to the swim bladder. This can lead to '''buoyancy problems'''.
==Diagnosis==
Diagnosis relies on the '''measurement of nitrite levels''' in the system or tank water, and some gross evidence of methaemaglobinaemia.
Toxicity levels vary between species of fish, but it is preferable to keep levels as low as possible in all cases.
==Treatment and Prevention==
Nitrite is much less toxic when '''chloride''' is present, possibly because chloride inhibits nitrate absorption across the gills.
'''Sodium chloride''' is the most available and cheapest source of chloride.
Haemaglobin levels should return to normal within 12-24 hours. If severe anaemia is present '''recovery may take weeks'''.
The original cause of the nitrate toxicity should be resolved and levels of nitrate in the water can be reduced through '''water changes, biological filtration and decreased feeding'''.
Prevention involves ensuring an '''adequate levels of chloride''' in the water at all times. Most waters already have enough chloride and prophylactic treatment is unnecessary.
{{Learning
|flashcards = [[Ornamental Fish Q&A 13]]
}}
==References==
Noga, E. (2010) '''Fish Diseases: diagnosis and treatment''' ''John Wiley and Sons''
Gupta, R. (2007) '''Veterinary toxicology: basic and clinical principles''' ''Academic Press''
Dietrich, H. W. (2009) '''Essential Zebrafish Methods: Genetics and Genomics''' ''Academic Press''
[[Category:To Do - Helen]]
[[Category:To Do - Review]]