PRINCIPLE & PRACTICES OF BIOFLOC AQUACULTURE TECHNOLOGY–A KNOW HOW (Part-2)
STEPS FOLLOWED IN THE CONSTRUCTION OF BIOFLOC SYSTEM
Step 1: Tank or Pond set-up & management
Generally, microbes, minerals, and heavy metals naturally present in soil can easily change the parameters of pond water and also affect the natural process of biofloc system.So for new biofloc set-up, it’s better to construct with lined pond, concrete ponds or indoor tanks where the soil has no connection with the water parameter of biofloc processes.This indoor tank may need sunlight for the production of algae because without sunlight algae can’t grow sufficiently.If the biofloc system based solely on bacteria then it’s called “Brown biofloc systems”In case of the large pond, install bottom drainage to remove the excess sludge. This is important when the addition of carbohydrates regularly creates more sludge to the pond bottom.We can use the biofloc reactor to influence the conversion of pond sludge to biofloc.
Step 2:
Provide Sufficient Aeration.
After the selection of the right pond or tank set-up, we need to look at the Aeration system. In the case of a pond, Paddlewheel aerator, used.Biofloc systems require constant aeration to maintain a high oxygen level & to avoid the solids from settling.Without aeration, the areas rapidly lose oxygen & convert it anaerobic zones which releases more amount of ammonia & methane.Biofloc system requires:6 mg of oxygen/lit/hr and for that required to start with at least 30 horsepower of aerator/ha.Paddlewheel system should be installed in such a way that the current is generated in the pond.for tarpaulin tanks magnetic aerator or ring aerator can be installed with airstones
Step 3:
Pre-seeding of culture water.
To increase the development of the biofloc system & stabilize the pond faster, pre-seeding of culture is important.It could be done by the addition of commercial or homemade recipes to culture water for the production of probiotics & prebiotic microbes.
Step 4:
Selection of species & maintaining stocking density
Generally wholly or partially filter feeders species are good for culturing in biofloc system.Examples are various shrimp species and tilapia are excellent candidates because they feed on biofloc and improving the feeding efficiency & FCR (feed conversion ratio) of a farming system.Stocking density of shrimp around 150 to 250 post larvae/m2 & tilapia stocking density would be 200 to 300 fry/m3.Higher stocking density may increase the risk of disease & deteriorate the health of the species.
Step 5:
Balancing Carbon sources
Biofloc or Raceway system maintains a sufficient amount of carbohydrates.Carbon present in these carbohydrates promotes heterotrophic bacteria to multiply and synthesize ammonia so maintain the water quality parameters.Ammonia produced from the nitrogenous feed as a metabolic product & pollutes the water quality. So to prevent it Biofloc system is important.It is advisable that carbon sources and feed mixtures with carbon-to-nitrogen ratio (C/N) above 10 imply the growth of heterotrophic bacteria.By reducing protein content in the feed we can reduce the production of ammonia.incase of over ammonia content in the water, molasses need to be added in proportion to maintain the C/N ratio and calculation is easy but sometimes difficult to farmers.
Step 6:
Biofloc Growth & management.
Due to strong aeration, a sufficient amount of natural light, temperature & available nutrient source, the number of biofloc starts multiplying frequently.Monitoring and maintaining these flocs would be done by using a cone-shaped beaker to collect water samples at the depth ranging from 15 cm to 25 cm in the afternoon.The solid particles should be left for settling at least 20 min. & they will easily stick to the sides of the beaker for making it easy to count.Regular monitoring of water samples is needed to check the pond water quality.In the case of outdoor biofloc, it consists of green algae, utilizes sunlight for their growth and bacteria use to consume the leftover feeds, byproduct & wastes.The Green colour of pond indicates multiplying of algae & brown colour indicating bacterial colonies start dominating in a pond.
Step 7:
Controlling water quality parameter.
When the biofloc system of pond or tank turns brown, increase the rate of aeration to sustain a high respiration rate.This is a more sophisticated stage as any power failure can reduce the total crop failure due to lack of oxygen & heterotrophic bacteria start producing ammonia.A large diesel generator, including a back-up generator, should be kept for the large farming system.
DIFFERENT WATER QUALITY PARAMETERS
Dissolved oxygen (DO) – > 4.0 mg/lit. & 60% of saturationTemperature – 28 to 30PH – 6.8 to 8.0
Salinity – 0 to 50 ppt (Depending on species)
TAN (Total Ammonia Nitrogen) – < 1.0mg/lit
Nitrate – 0.5 to 20mg/lit
Nitrite – < 1.0 mg/lit
Alkalinity – > 100 mg/lit
Orthophosphate – 0.5 to 20 mg/lit
Settling solid (SS) –5 to 15 ml/lit for shrimp5 to 20 ml/lit for tilapia fingerling20 to 50 ml/lit for tilapia juvenile.
Total suspended solid (TSS) – < 500 mg/ lit
Step 8:
Monitoring of the farm status
After monitoring the water quality without the exchange of water, the 2nd important thing is to improve growth rates & feeding management.For that regularly check the monitoring of farm stock, recording growth rates, appearance, FCR & stock survival is needed.It has been found that every unit growth of species an additional 0.25 to 0.5 units of growth come from the biofloc system.
Step 9:
Cleaning after Harvesting
It is advisable that after harvesting the species cleaning is an important step to maintain good biofloc systemReuse of the culture water may build up the increasing number of microorganisms & causes serious risk.Also, the heavy metals used to build up in culture water which is accumulated in the stock & make unsuitable for human consumption.So cleaning up is important before starting a new batch of culture.
Advantages of the Biofloc culture system
Biofloc culture is Eco-friendly in nature & cost-efficient in case of feeding management.It gradually reduces the environmental impact & mitigation by controlling water quality parameters.This system requires less land area & water supply. Also, use a limited or zero water exchange system.Provide a higher rate of productivity by enhancing growth, survival rate &feed conversion in a culture system.Higher biosecurity rate with reduced contamination by human maintenance & supply
Reduces pollution in water, disease outbreak into the system & prevents the spread of pathogens in water.Reduces utilization of protein-rich feed in the system & also cost of feed. Use of cheaper fish species and trash fish feed formulation.
Disadvantages of the Biofloc culture system.
It is an energy-intensive process, requires a high amount of energy during mixing aeration.Response time is reduced due to the increasing rate of respiration.This system requires an extra start-up period for culturing the high-value species.Require Alkalinity supplementation which acts as a pH buffer that supplies CO2 for the photosynthesis of algae & plant in water.Due to the accumulation of nitrate from waste product water pollution increases.Unavailability of sunlight every time the growth of algae suppressed in the culture system.
Reference-On request
