Monitoring ammonia

Ammonia monitoringAmmonia is the major waste product of protein or nitrogenous metabolism in fish and other aquatic organisms. The major source of nitrogen compounds in fishpond culture is the protein contained in the feed. Therefore, the rate of ammonia production of fish is proportional to the feeding rate. It is excreted primarily across the gills, and in urine and faeces. Ammonia is also produced during the aerobic decomposition of organic matter by bacteria.

In water, the total ammonia-nitrogen (TAN) occurs in two forms, unionised ammonia (NH3) which is toxic to fish, and the ammonium ion (NH4) which is relatively non-toxic, except at extremely high concentrations. Ammonia can change from one form to the other creating a balance between the two forms. Water pH and temperature influence the proportion of total ammonia occurring as the toxic (NH3) form.

Consequently, water samples are taken for TAN levels in the afternoon when pH and temperature are at the daily maxima. Ammonia levels then decrease during the night. To determine the concentration of the toxic NH3 form, a simple formula is applied using a chart showing the percentage of TAN in the NH3 form at different temperatures and pH values (Table 1). For example when the temperature is 20°C and the pH is 9.4, 50% of the TAN is present as NH3 if TAN is 2.0 mg/l, NH3 is 1.0 mg/l.

Silver perch can be successfully grown between levels of 0 - 0.1 mg/l NH3; prolonged exposure to concentrations over 1.0 mg/l adversely affects growth, and concentrations of 1.0 mg/l and higher may be lethal.

Signs of High Ammonia:

  • abnormal swimming behaviour including lethargy
  • reduced feeding
  • congregation around water inlet or pond edges
  • fish showing the above signs in the afternoon but recovering during the night.

Effects of High Ammonia:

  • gill damage
  • reduced growth rate
  • increased susceptibility to diseases
  • elevated blood pH
  • tissue and internal organ damage
  • poor osmoregulation
  • death.

Causes of High Ammonia:

  • high feeding rates
  • decomposition of organic matter by bacteria.

High Ammonia - What can I do?

  • reduce or stop feeding
  • flush pond
  • reduce the stocking density
  • aerate the pond
  • in emergencies - reduce pH of pond.

Table 1 Percentage of total ammonia-nitrogen (TAN) in the toxic unionised form NH3 at different temperature and pH values. From Boyd (1982) "Water quality management for pond fish culture".

pH

Temperature ( °C)

 

8

12

16

20

24

28

32

7.0

0.2

0.2

0.3

0.4

0.5

0.7

1.0

8.0

1.6

2.1

2.9

3.8

5.0

6.6

8.8

8.2

2.5

3.3

4.5

5.9

7.7

10.0

13.2

8.4

3.9

5.2

6.9

9.1

11.6

15.0

19.5

8.6

6.0

7.9

10.6

13.7

17.3

21.8

27.7

8.8

9.2

12.0

15.8

20.1

24.9

30.7

37.8

9.0

13.8

17.8

22.9

28.5

34.4

41.2

49.0

9.2

20.4

25.8

32.0

38.7

45.4

52.6

60.4

9.4

30.0

35.5

42.7

50.0

56.9

63.8

70.7

9.6

39.2

46.5

54.1

61.3

67.6

73.6

79.3

9.8

50.5

58.1

65.2

71.5

76.8

81.6

85.8

10.0

61.7

68.5

74.8

79.9

84.0

87.5

90.6

10.2

71.9

77.5

82.4

86.3

89.3

91.8

93.8

 

Example: To obtain the concentration of NH3: water at pH 8.4, 28°C and 2 mg/l of TAN (TAN has already been determined by sampling) contains:
15% of 2 mg/l
2 mg/l x 15.0 (from chart) ¸ 100 = 0.3 mg/l of NH3