Animal Science

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Unit

• Animal Science

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Problem Area

• Aquaculture

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Lesson

• Microbial Cycling of Nitrogen

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Student Learning Objectives

• 1. Describe the steps of the nitrogen cycle in
  an aquaculture system.
• 2. Identify forms of nitrogen that are harmful
  to aquaculture species.
• 3. Identify factors which influence the toxicity
  of nitrogen in an aquaculture system.
• 4. Explain procedures for controlling harmful
  levels of nitrogen in an aquaculture system.

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Terms

• Ammonia
• Ammonia toxicity
• Ammonification
• Ammonium
• Denitrification
• Nitrate
• Nitrification

• Nitrification
• Nitrite
• Nitrite toxicity
• Nitrobacter
• Nitrogen gas
• Nitrosomonas
• Total ammonia nitrogen

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What is the nitrogen cycle in an aquaculture
system?

• Nitrogen is cycled through the biosphere
  constantly.
• A. In aquaculture facilities four forms of
  nitrogen are likely to be found ammonia (NH3 ),
  ammonium (NH4 ), nitrite (NO2 ) and nitrate (NO3
  ).
• B. Ammonia compounds in water are produced as a
  result of decomposing organic matter through the
  ammonification process. Sources of organic matter
  in an aquaculture system include uneaten feed,
  fish waste, decaying plants and bacteria. Ammonia
  is converted to nitrite by nitrosomonas bacteria
  by the process of nitrification. Gaseous ammonia
  can be lost into the atmosphere by diffusion.

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• C. Nitrite is converted to nitrate by the
  nitrobacter bacteria through an oxidation
  reaction. Nitrates are converted to nitrogen gas
  (N2 ) in anaerobic conditions and diffused into
  the surrounding atmosphere. This process is known
  as denitrification.
• D. Nitrates that are not denitrified are used by
  phytoplankton, higher plants and bacteria as a
  nutrient source. Fish can then consume these
  organisms beginning the cycle again.

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What forms of nitrogen are harmful to aquaculture
species?

• A. Total ammonia nitrogen (TAN) levels are
  considered when determining ammonia toxicity. TAN
  includes unionized ammonia (NH3 ) and ammonium
  (NH4 ), the ionized form. Ammonia is 75100
  times less toxic than ammonium. Death can occur
  when ammonia levels reach 2 ppm and losses
  increase when above 7 ppm. Brain damage, increase
  susceptibility to disease, and slower growth are
  often seen when ammonia toxicity occurs.

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• B. Nitrite causes the hemoglobin in blood to
  oxidize rendering it unable to absorb and carry
  oxygen. This is a similar to the Blue Baby
  Syndrome in humans. Nitrite toxicity occurs at
  much lower levels than ammonia. Nitrite levels
  greater than 1 ppm can cause fish death.

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What factors influence the toxicity of nitrogen
in an aquaculture system?

• Temperature, pH and chloride concentrations are
  factors that influence the toxicity of nitrogen
  in an aquaculture system.
• A. Unionized ammonia is more toxic at warmer
  water temperatures and at high pH. Ionized
  ammonia and unionized ammonia exist in
  equilibrium. As pH increases more unionized
  ammonia is present.
• B. Nitrite toxicity is reduced by the presence of
  chlorides in water. The addition of sodium
  chloride or calcium chloride can reduce the
  nitrite poisoning.

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What procedures are used to control harmful
levels of nitrogen in an aquaculture system?

• Methods of controlling nitrogen levels include
  cultural and chemical means.
• A. Cultural methods of controlling nitrogen
  levels include the population density control,
  proper feeding, removing excessive organic
  material, adding fresh water, and monitoring pH
  levels.
• B. Chemical means includes the addition of acidic
  compounds to maintain the proper pH and the
  addition of chloride compounds to decrease the
  toxicity of nitrite.

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Review/Summary

• What is the nitrogen cycle in an aquaculture
  system?
• What forms of nitrogen are harmful to aquaculture
  species?
• What factors influence the toxicity of nitrogen
  in an aquaculture system?
• What procedures are used to control harmful
  levels of nitrogen in an aquaculture system?