Aquaculture enterprises have always faced difficulties due to ammonia.
Controlling ammonia is of the utmost importance to aquaculture as even moderately high ammonia levels can have a detrimental effect on fish flavor, it can lead to higher than acceptable rates of mortality, and it can have an extremely negative effect on the bottom line. Taking control of ammonia levels requires a basic understanding of why ammonia levels build up and how they can be removed.
Ammonia is a free nitrogenous compound, others are nitrate and nitrite. In natural rivers and lakes, levels of free nitrogenous compounds tend to be low. These compounds are locked up in the plant and animal life of the river. In an aquaculture pond, however, the density of the fish population is much higher than would ever occur in nature and this leads to potential problems with free nitrogenous compounds, especially ammonia.
The primary means of Nitrogen contamination and the primary source of ammonia in aquaculture ponds is fish waste. As fish wastes are broken down by heterotrophic bacteria, ammonia is created. In environments where plant life including algae is discouraged, there is little that will absorb the ammonia from the water. The concentration will rise until the fish become comatose and die unless some form of action is taken to remove it from the water.
High Ammonia Levels
High ammonia levels are evidenced in aquaculture ponds in a number of ways.
Algae tend to bloom when there are excessive free nitrogenous compounds, making the water green as a result of the algae presence. Fish from ponds with excess ammonia will have poor flavor. The fish will be prone to disease, may appear stressed, and mortality rates are likely to increase beyond their usual levels. Finally, oxygen levels will decrease. From the severity of the above symptoms, it is quite obvious that ammonia is not a mild water chemistry issue but rather a major threat to the productivity and profitability of any aquaculture enterprise.
How Much Ammonia is too Much?
A common question with relation to ammonia levels is, "how much is too much?"
It is actually rather a complicated question to answer as there are vast differences in the concentrations of ammonia that different fish species can handle. This is further complicated by the fact that there is significant variation in toxicity depending on pH and water temperature.
Lower temperatures and higher pH will make lower levels of ammonia toxic to fish. Certain fish are extremely vulnerable to elevated ammonia levels and will be adversely affected by levels that other species can tolerate.
For freshwater species the range of 0.53 to 22.8 mg/L is generally regarded as toxic, but problems will begin to occur from amounts greater than 0.1 mg/L. At over 0.1 mg/L skin, eye, gill and internal organ damage can occur.
Some experiments have shown gill injury from
rates as low as 0.002 mg/L in salmon fingerlings
when they are exposed for six weeks or more.
As ammonia levels within the safe level increase,
growth rates and hatch rates will be reduced.
How much ammonia is too much? One might argue
that any ammonia is too much.
to Part 2 >>