Fish depend on their aqueous environment to provide oxygen and nutrition to support respiration and growth. However, the water that supplies materials for growth is simultaneously receiving waste products like carbon dioxide and ammonia from the fish.
Water quality management in aquaculture maintains the balance between the life support and waste disposal functions of water.
To be a successful fish farmer, you must routinely determine if the water quality is suitable for fish culture and what treatments may be required to correct poor water quality.
A fish farmer’s most valuable tool in water quality management is chemical testing. Routine testing helps prevent fish losses that result from poor water quality or stress-induced disease that results from marginal water conditions.
In addition, monitoring water quality provides the grower with valuable information about natural chemical cycles, daily and seasonal, that are operative in the system.
Chemical test kits provide simple, inexpensive analytical methods adapted for field use. Manufacturers offer combination kits that can perform a complete water quality profile as well as single-function kits for special needs or more simplified testing requirements.
Test kits vary in price, quality, and accuracy varying from semi-quantitative visual comparators and drop titrators to research grade electronic colorimeters, dissolved oxygen (DO) and pH meters.
In selecting a test kit, it is important to determine the level of accuracy you require and the number of tests to be performed daily. Whatever test kit you select, a complete water quality profile can usually be performed for less than a dollar per day in 15 minutes or less.
What to Test:
Critical Chemistry. Includes chemicals that are most likely to cause fish mortalities.
- Dissolved oxygen (DO) - Highly variable with temperature, wind activity, phytoplankton photosynthesis and night respiration.
- Ammonia - A direct excretory product of fish. The toxic unionized form increases with temperature and pH.
- Nitrite - An intermediate in the nitrogen cycle. Bacteria (Nitrosomonas sp.) convert ammonia to nitrite; nitrite may then be converted to nitrate (Nitrobacter sp.) which is not toxic.
Water Condition Factors. Chemistry that can indirectly influence toxicity.
- Alkalinity - Includes the bicarbonate concentration of the water. An indication of the buffering capacity or the water’s ability to resist changes in pH.
- Hardness - The calcium and magnesium concentration of the water. Low calcium can interfere with development of some species.
- pH - The acidic or basic condition of water. A range of 6-9 is fairly common in low alkalinity ponds.
Some fish farmers may find additional testing is necessary. For example, at high fish densities, carbon dioxide can be a problem. In other cases, monitoring iron, chlorides or hydrogen sulfide may be necessary.
Depending on the frequency of testing, many fish farmers find that electronic analytical instruments are helpful; for example, DO and pH meters can be invaluable in operations that require frequent testing of a number of ponds. In some fish farming operations, testing can be simplified.
The trout grower using water from a limestone spring is less interested in alkalinity and hardness than the hybrid striped bass grower using a recirculation system so testing for these factors could be reduced or eliminated.
Frequency of Testing:
How often you should test can vary with the aquaculture system. For example, a recirculation system supporting one pound per gallon of hybrid striped bass will require more frequent monitoring than an open pond system containing 1,000 pounds per acre of channel catfish.
Components of critical chemistry should be monitored frequently. Under conditions where DO is likely to be limited (e.g., high water temperature, high fish stocking density, excessive algae growth), oxygen tests may be required several times during the night and day.
It is advisable to check ammonia and nitrite levels daily during start-up or until the operator has gained some familiarity with the variation of nitrogen components in the system. Although pH in the range of 6-9 is not likely to be directly toxic to fish, pH levels determine the concentration of the unionized or toxic form of ammonia and should be measured at the same time.
The water condition factors alkalinity and hardness are less variable than the critical chemicals. At high alkalinity (100 ppm), pH is less variable due to the buffering capacity of bicarbonate. In open pond systems, weekly testing of alkalinity and hardness is sufficient; recirculation systems may require more frequent testing.
Treatments:
Testing provides information that can be used to determine if water chemistry is unsuitable for fish culture and to determine the treatment necessary to correct water quality problems. A regular testing program and careful use of corrective treatments will minimize the risk of fish loss to poor water quality and secondary losses to stress induced disease.
Treatment chemicals suggested are commonly used in other agricultural applications. Check with your local farm supply store for availability and pricing.
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