By Dr S.Rajamanickam, Technical officer,ICAR-CIBA
“Biofloc Technology”: The use of aggregates of bacteria, algae, or protozoa, held together in a matrix along with particulate organic matter for the purpose of improving water quality, waste treatment and disease prevention in intensive aquaculture systems. Consumption of bioflocs also provides nutritional value to cultured species.
BIOFLOC Technology for Vannamei and Tilapia Aquaculture Technology:Water quality is important in any aquaculture production. Negligence in monitoring the water quality parameters might bring to a big loss to the farmers. RAS and biofloc both involve water quality monitoring, but they are slightly different in the parameters which depend on what animals you are culturing. Biofloc technology is a popular aquaculture practice as it is more sustainable to the economy and environment. This article will give a broad idea of what are the most important parameters to monitor when practicing biofloc technology.As biofloc technology practices zero water exchange, we can see a high accumulation of solids in the water. These solids come from dead organisms, feces, and leftover feed. Settleable solid is a form of solid that can settle on the bottom within one hour. Imhoff cones can be used to measure settleable solid in the biofloc water. High settleable solid will result in high turbidity to the water and compete for dissolved oxygen with the cultured organism. In fact, we have to maintain the settleable solid within the range of 10-15 ml/L. As cultured organisms continue to grow for a few months, there is always a time where the settleable solid will be very high and need fast action before it goes out of control. Commercial action that can be applied to remove this excess solid is by changing water or using a settling tank. The general concept of settling tanks is to pump in the biofloc water into a separate tank at a very low velocity (5 liter per minute), so that the solid will settle inside the settling tank and be easily removed.
Dissolved oxygen:
Oxygen is crucial in biofloc technology. Optimum level for dissolved oxygen is at 5 ppm, depending on the cultured organism. Some farmers have issues with dissolved oxygen in their biofloc system which resulted in mass mortality to their cultured organism. It is well known that plants can produce oxygen through photosynthesis. Small plants including algae are available in the biofloc water and they can undergo photosynthesis. However, the algae can only produce oxygen during the day time, from dust to dawn. Dawn is the time when we can measure a high amount of oxygen due to the photosynthesis that occurs for the whole day time. The problem arises when night time comes, where there is no photosynthesis and only respiration happens in the water. The night time is where the oxygen crash occurs and causes mortality of the cultured organism. To avoid excess consumption of the oxygen by the cultured organism and other microbial communities in biofloc, we need to understand and adjust the feeding. This is because, when the cultured organism feeds, they will consume more oxygen to convert the food to another form of energy in their body. Usually, the feeding will be given three times (Morning, lunch and evening). So, if we measure the dissolved oxygen at a low level, it is important to adjust the feed to lessen it during the morning feeding because we know that the dissolved oxygen level will be lower at that time. For farmers who wish to run higher stocking density in their culture, it is suggested to give oxygen supply to the biofloc system. This can be done by increasing the saturated oxygen through an air pump or injecting pure oxygen especially during the morning feeding or maintaining a good aeration to the water.
Total ammonia nitrogen (TAN):
TAN is the sum of the concentration of ionized ammonium, NH4+ and unionized ammonia, NH3. TAN in the water can come from dead organisms, feces and leftover feed. TAN is produced when the microbial community in the water decomposes those leftover through nitrification process. That is why it is important to remove the dead body, any feces, and excess feed immediately as much as possible. This action can prevent a high ammonia level in the biofloc water. Otherwise, if the TAN level persists more than 1.0 mg/L in the water, it is alarming that our microbial community is not well established and needs more carbon sources as their food. Carbon can be supplied into the biofloc based on the carbon to nitrogen ratio. Excess addition of the carbon may have resulted in high settleable solid which probably messed up other water quality parameters. Source of carbon can come from flour, white sugar, soya bean flour, maize flour, Ricebran flour,tapioca flour,molasses, lactose and a variety of starch have been added to develop hetrotrophic bacteria population in the system @ 1ppm,to promotes C:N ratio 10:1 to 15:1(or) 20:1
Temperature:
Some farmers do not always pay attention to the temperature. Yet temperature can affect most of the chemical reactions inside the biofloc water. Aside from that, temperature can affect the cultured organism’s behavior, feeding rate and growth. For example, frequent fluctuations of the temperature make the organism consume more oxygen for them to adapt to the current temperature. More oxygen consumption means more biological oxygen demand in the water. When most of the energy is used to adapt to the current temperature, there is less energy left for the organism to eat and increase body growth. As a farmer, our concern is the total mass yield of the culture organism to be more profitable during the harvesting period. Getting larger yield production is a sign of good water quality monitoring, which reflects the culture organism gets sufficient amounts of nutrients.
As a conclusion, these four parameters most likely the vital water quality involve in operating biofloc technology. Basic knowledge and understanding is a good start to make sure farmers know how to handle and solve the arising issue afterward. Quick and smart solving action is a big matter in the aquaculture industry as it involves economical concern. Being efficient in operating aquaculture is a great achievement!
