Table 1.5 Stepwise determination of un‐ionized ammonia.
| STEP | ACTIVITY |
|---|---|
| 1 | Measure pond TAN with commercial test kit |
| 2 | Measure Pond temperature |
| 3 | Measure Pond pH |
| 4 | Find the multiplication actor in Table 1.1 using the pond temperature and pH |
| 5 | Multiply TAN and factor from step 4 to determine un‐ionized ammonia nitrogen |
TAN, total ammonia nitrogen.
1.5.1 Biofilms
Millions of bacteria and viruses are found in every milliliter of water in a healthy aquasystem and on every surface, and they comprise very complex ecosystems called biofilms. The relationship between beneficial and pathogenic organisms is very complex. Culturing bacteria only identifies less than 1% of the bacteria in water. Current technologies such as quantitative polymerase chain reaction are demonstrating a vastly diverse microbial ecosystem. A managed system demonstrated over 890 genera and over 2500 species of bacteria which only accounted for 69% of the bacterial DNA; the rest were unidentified (Stamper, 2015).
Aquatic microorganisms occur in two realms: planktonic and sessile. The planktonic state is fairly straightforward, whereas the sessile biofilm ecology is extremely complex. Biofilms include organisms beyond bacteria and comprise fungi, algae, protozoans and metazoans. An intricate ecological process occurs as various environmental parameters change. These organisms secrete an assortment of chemicals known as extracellular polymeric substances, which add to the total organic carbon within the water column and are critical to the health of the organisms and water environment (Stamper, 2015; Tepper, 2019).
An important consideration in any aquatic system is the potential for pathogenic bacteria to create a biofilm that will allow it to persist in a tank or other culture system. Biofilm formation and disinfection can be especially problematic in recirculating aquaculture systems. Once a highly pathogenic organism is introduced, it can persist in the system indefinitely and continue to cause recurrent disease outbreaks.
Secreting a protective coating can allow bacteria to survive desiccation and standard cleaning techniques. If recurrent bacterial disease becomes an issue in cultured species, additional disinfection of the system may be indicated. This may require depopulation while strong disinfectants are used, following a period of dewatering and drying of the system. Physical methods such as heat and pressure washing can be used and a combination of physical and chemical treatment techniques may increase the effectiveness of the disinfection.
1.5.2 Chemical Flocculation and Bioflocculation