Ammonia control in aquaculture - taking steps to prevent ammonia related health problems

Limited water exchange, high stocking density, and high protein feed to maximize growth rates; modern intensive aquaculture ponds often have problems with ammonia, nitrite, and other pollutants that stress the animals and open the door to disease. With several requests for an immediate ammonia response in problem ponds, I wanted to detail how to prevent the problem by good maintenance and how "nitrifiers" or AOB with their short shelf life and refrigeration requirements are not a good thing to add in almost all ponds.

First, ammonia in aquaculture comes from problems in the pond nitrogen cycle. As in nature, decaying animal wastes and excess feed (found in the pond bottom sludge) convert from organic nitrogen into ammonia. Ammonia can kill an aquaculture pond outright while still at less than 10 mg/L. Even at "manageable" levels, ammonia stresses the organisms which lowers feed conversion rates and weight gain. 

Ammonia can be removed from water in several ways from greatest to least important

• Algae thrives when given ammonia as a nutrient 
• Heterotrophic microbes use ammonia to fuel growth and make proteins
• Chemotrophic ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) exist in low concentrations in biological floc

So how do I see ponds likely to have ammonia problems during the grow out? Look at bottom sludge. This sludge is reservoir that continues to produce ammonia as organic solids decay. Of course overfeeding high protein feeds can exacerbate the problem. Now for the solution:

• Check pond bottom sludge levels prior to stocking 
• Ensure aerators are in working order 
• Use the correct feed composition and feeding rates
• Stock at appropriate density
• Adding heterotrophic waste degrading bacteria from the start of the season helps (adding before you get highly polluted water is key).
  
  

Benefits of adding heterotrophic bacteria:

• Organic wastes, including sludge, are consumed by microbes. This happens naturally, but often with high stocking density & feeding, you have waste buildup and start of problem anaerobic conditions (often seen as black sludge with hydrogen sulfide). 
• Microbes under low oxygen conditions (pond bottom) use nitrate/nitrite as alternative electron acceptor - this prevents inhibition of AOB/NOB activity
• Microbes in quality products also help reduce pathogenic bacteria growth via competitive exclusion
• Beneficial immune stimulation by select probiotic cultures 
• Promotes green algae (eukaryotic) organisms growth. Remember these microbes remove more ammonia from pond water than any other organisms.

We have done studies on the microbiome of successful aquaculture systems and found which microbes are associated with healthy ponds. The bacteria we selected for aquaculture products are not "superbugs" or GMO - they are concentrates of the beneficial microbes found in healthy ponds. Sometimes, the natural balance seen in healthy ponds is upset by stocking densities and feed rates. We just help restore the balance.
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Key point is to monitor the pond for pH, Dissolved Oxygen, Sludge Layer frequently. If stocking at high density, adding microbes early on in the grow out season will prevent pollution problems later in the season.

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