As the human population continues to grow, food production industries such as aquaculture will need to expand as well. Shrimp farming has become competitive and as such the technology utilized needs to be efficient in all aspects- productivity, quality, sustainability, bio-security and to be in line with market demand. In order to preserve the environment and the natural resources, this expansion will need to take place in a sustainable way.

Three Goals of aquaculture
• The prime goal of aquaculture expansion must be to produce more aquaculture products without significantly increasing the usage of the basic natural resources of water and land.
• The second goal is to develop sustainable aquaculture systems that will not damage the environment.
• The Thirld goal is to build up systems providing an equitable cost/benefit ratio to support economic and social sustainability. All thease three prerequisites for sustainable aquaculture development can met by biofloc technology.

Biofloc technology is a technique of enhancing water quality in aquaculture through balancing carbon and nitrogen in the system. This technology has gained attention as a sustainable method to control water quality, with the added value of producing protein rich feed in situ. The basic technology was developed by Dr.YoramAvnimelech in Israel and initially implemented commercially in Belize by Belize Aquaculture. BFT has become a popular technology for Shrimp Nursery and Tilapia fish culture. It is possible that this microbial protein has a higher availability than feed protein.

Biofloc is an assemblage of beneficial microorganisms such as heterotrophic bacteria, algae, fungi, ciliates, flagellates, rotifers, nematodes, metazoans & detritus. Eventually the system becomes bacterial dominated rather than algae dominated and forms microbial flocs by utilizing the waste materials in the pond. As it contains predominantly heterotrophic bacterial community over autotrophic and denitrifying bacteria, this can be controlled by maintaining high carbon to nitrogen ratio (C:N). Autotrophic bacteria can only convert 6% of the inorganic nitrogen into organic nitrogen, while heterotrophic bacteria could convert nearly 100% of the inorganic nitrogen into organic nitrogen. Moreover, the growth rate of heterotrophic bacteria is equivalent to 10 times that of autotrophic bacteria.With zero or minimal water exchange, Pathogens are removed in the biofloc culture so biofloc is considered as eco-friendly approach. The function of the biofloc is to reduce the nitrogenous metabolic waste (ammonia, nitrite) produced by feeding and production.pH and Nitrogen levels in water are the biggest concern in aquaculture.In BFT system, heterotrophic bacteria utilize the ammonia and nitrite from the BFT tank and grows in numbers by reproduction. That Bacteria converts harmful ammonia and waste matters into proteins. These microbial proteins used as food source for shrimps.

This is a relatively new technology to support high density, better disease management, better water quality, water conservation, high bio-security, lower feed requirement, ultimately resulting in reduction in the production cost. By using this technology, Shrimp farmers could safely go for high-density farming.

The concept of biofloc technology worksaround the formation of dense heterotrophic bacterial community.The main principle of the Biofloc technique is the generation of nitrogen cycle by maintaining a higher C:N ratio by stimulating heterotrophic microbial growth, which assimilates the nitrogenous waste that can be used by the culture species, in situ as a feed. The Biofloc system is not only effective in treating the waste but also grants nutrition to the aquatic animal. The optimum C:N ratio in an aquaculture system can be maintained (C:N ratio 12-15:1) by adding different locally available cheap carbon sources and / or reducing protein percentage in feed.

• Biofloc based shrimp farming is found to be highly profitable in terms of better growth performance, disease resistance and rate of return over investment compared to conventional farming.
• The stocking density of animals in HDP-lined biofloc pond is twice the density of anconventional shrimp pond.
• In conventional farming, nitrogen is flushed out through water exchange every 25-30 days to keep animals stress-free and disease-free. The bioflocs use up the nitrogen and convert it into microbial proteins, for the shrimps.
• Production per unit area is high in biofloc system. Production per hectare in a conventional pond is 10-15 tonnes, while a biofloc pond gives out 20-30 tonnes.
• It costs about Rs.14 lakh per hectare for a biofloc pond, thrice as much as a conventional pond. But the capital investment is out-weighed by the benefits of the system. There is no dry-out season in BFT,as it can be easily disinfected and the ponds are crop ready immediately.

To accelerate the development of biofloc system and stabilisethe pond faster, it is advisable to pre-seed the culture water. This can be done by adding a number of commercial water probiotics to the culture water.

Biofloc system works best with species that are able to derive some nutritional benefits from the direct consumption of the floc. Biofloc system is most suitable for species that can tolerate high solid concentration in water and are generally tolerant of poor water quality. These species are wholly or partially filter feeders. Shrimp is anexcellent candidate, as they gobble up bioflocs, thereby dramatically improving the feeding efficiency and FCR of your farming operation.High stocking densities can be considered and it is common to stock shrimps in ponds at densities of 130-150 (PL10)/m3.

To prevent ammonia problem at the start of the farming cycle, biofloc is a good option. Growth and development of biofloc in the culture system is ensured by sufficient availability of carbohydrates, initially. In addition to the commercial feed, a supplemental source of carbon must be added in order to stimulate production of the heterotrophic bacteria and reduce the nitrogenous waste. The carbon in these carbohydrates enables heterotrophic bacteria to multiply and degrade ammonia, thus maintaining water quality.Most of the Shrimp feeds have a carbon to nitrogen (C:N) ratio of approximately 7–10:1.Additional inputs are needed to raise this ratio to between 12:1 and 15:1.Heterotrophic bacteria would prefer a ratio of approximately 12–15:1.

Biofloc systems require constant motion to maintain both high oxygen levels and to keep solids from settling. Increasing the heterotrophic bacteria population also increases the total oxygen demand of the tank. Heterotrophic bacteria require oxygen for life processes such as ammonia assimilation.Additionally, organic solids in the water column reduce the ability of that water to hold as much oxygen. Oxygen must be added either through aeration with atmospheric air and perhaps supplemental compressed or liquid oxygen. Areas without movement will rapidly lose oxygen and turn into anaerobic zones which release large amounts of ammonia and methane. Biofloc systems require up to 6mg of oxygen per litre per hour and it is recommended to start with at least 30 horsepower of aerators per hectare.High aeration 28-32 Hp/Hectare must be given to shrimps. Number of aerators and positioning to help biofloc in suspension condition in the water.

Dissolved oxygen content of the water of fish ponds is one of the most important parameters of water quality, as the oxygen is a vital condition for all the organisms living in the water and having an aerobic type of respiration. The solubility of oxygen is influenced by several factors (e.g. air pressure, hydrostatical pressure, salt content), but in aquaculture farms it is generally enough to consider only water temperature.

Air is a mixture of different gases. The air in Earth’s atmosphere is made up of approximately 78 percent nitrogen and 21 percent oxygen. Air also has small amounts of lots of other gases, too, such as carbon dioxide, neon, and hydrogen.Oxygen in air is about 21%. When webreathe, we inhale 21% oxygen and release 4% CO2. It is in gaseous form. In oxygen cylinder, the concentration of oxygen is 98%, means it is very pure oxygen. You inhale 98% oxygen at one time. It is in liquid form. Oxygen generally is a gas, which means air, but in cylinders its filled up pressurized and is in a bit liquified when compressed to fill up in cylinders, due to compression it turns its state of matter from gas to liquid(condensation), which is stored in cylinders. Oxygen through aerators is cheaper than pure oxygen. Commonly, 1 hp aeration is required for each 400-500 kg shrimps. 1 hp for each 8-10 kg/ha/day of feed input have given.

An aerator in practical use will not transfer as much oxygen as suggested. The main reason is that the rate of oxygen transfer decreases rapidly as dissolved oxygen concentration increases.Oxygen transfer rate also decreases slightly in response to greater salinity or greater suspended solids concentration, and it increases with higher water temperature.As dissolved oxygen concentration steadily rises during daytime in ponds because of photosynthesis, aerators become progressively less efficient in transferring oxygen.Aerators transfer oxygen from water to air when water is supersaturated with dissolved oxygen.

Less aeration usually is needed in the daytime than at night.Ponds usually are at near dissolved oxygen saturation or even supersaturated with dissolved oxygen from 10.00 am to 4.00 pm.Generally, the period of lowest dissolved oxygen concentration will occur between 1.00 am and 7.00 am.Early in the grow-out period, less aeration is necessary because of lower oxygen demand.The aerators to be operated daily during a particular period during the crop should all be operating during this critical 6-hr time interval.

Hopkins et.al. (1991) have clearly demonstrated that it is possible to obtain 500 kg/hp with factory made, floating, electric aerators.Many shrimp farmers run half of the entire installed aeration capacity or more during daytime throughout the entire crop period, and at night all aerators usually are operated.Do not install more aeration than necessary. A good rule is about 2 hp/t for floating, electric aerators and 3 hp/t for long-arm aerators.

Aeration requirement can be calculated fromfeed BOD, Hourly oxygen demand, minimum acceptable dissolved oxygen concentration and aerator performance rating.

Example:
Feed Input – 200 kg/ha/day
Average Aerator Efficiency (AAE) of aerator – 0.45 kg O2/hp/ha
Feed BOD – 1.05 kg O2/kg feed
Aeration requirement (hp/ha) = (200 kg feed/ha/day x 1.05 kg O2/kg feed) x 0.45 kg2/hp/ha 24 hour
= 19.4 hp ( 1 hp for 10 kg feed)
Using the equation and specific data on FCR, feed BOD and water quality, more exact determination can be made.
Most Shrimp Pond aerators operating at 28-32oC in water salinities of 15-30 ppt will have AAE values around 0.3-0.6 kg O2/hp/hr at the lowest dissolved oxygen concentration.

With plenty of aeration, sunlight and a readily available source of carbon, biofloc numbers should start to multiply quickly. Depending on a variety of factors, including water temperature, available nutrients and sunlight, the number of seeded bioflocs at the start of the operation, the number of suspended solids (flocs) will increase from close to zero to about four to five units per millilitre within a few weeks. Monitoring the growth of these flocs can be done by using a cone-shaped beaker, Imhoff settling cones to collect several water samples at a depth of 15cm to 25cm, preferably in the late morning. The solid particles should be left to settle for 10-20 minutes and reading taken by reading the graduations on the cone. Shrimp biofloc should maintain settleable solids at 10–15 mg/liter pond water. Readings should be taken at least once weekly.

Water samples must be regularly taken to monitor the pond water and determine the activity of the two biofloc types plus their respective densities. In simple terms, outdoor bioflocs consist of green algae and brown bacteria: the algae mainly utilise sunlight for their growth, while the bacteria mostly consume leftover feeds, their byproducts and associated wastes.Since algae initially tend to multiply faster, this means that a pond looks green at first, turning brown over the following weeks as bacterial colonies start to dominate.

Once the biofloc system has turned brown, aeration must be significantly increased to sustain the high respiration rate. Respiration rates at this stage can reach 6mg per litre per hour, requiring up to six times more energy per hectare compared with the start of operations. Any power failure at this stage can quickly result in total crop failure due to a lack of oxygen and because in a low-oxygen environment many heterotrophic bacteria actually start producing ammonia, which will fastly elevate and become highly fatal.Important parameters like alkalinity, hardness, TSS are under analysed.Alkalinity – 100-150 ppm, TAN < 1.5 ppm, Nitrite < 1 ppm, TSS – 250-400 ppm, Settleable solids concentration is 10-15 ml/L for shrimp under good biofloc system. Manage TSS< 300 ppm to reduce aeration requirements.

Besides maintaining water quality at lower cost and without water exchange, the second goal of a biofloc system is to improve growth rates and feeding efficiencies, thereby improving the profitability and sustainability of farming operations.

• Sludge has high BOD and Produces CO2, reducing pH - So its removal reduces O2 requirements.
• Routine removal of sludge with control of TSS < 400 ppm
• Need to keep floc in suspension and aerated to limit sludge accumulation
• From 6-9 weeks need to remove excess sludge every 1-2 days through central drain/sump or by submersible pump.
• Should be left with < 2% of pond covered in sludge

• Eco-Friendly culture system
• Reduces environmental impact
• Judicial use of land and water.
• Reduced pathogens
• Improvement of growth rate
• Effect on growth performance and immunity improvement in juvenile and sub adult stages of penaeid shrimps.
• Recycled the nitrogen metabolites as a natural feed
• Very high biosecurity minimized WSSV occurrence.(shrimp specific)
• Limited or Zero water exchange
• Production and carrying capacity are typically 5 to 10 percent higher than typical culture systems.
• Shrimp grows larger about 2 g higher than normal systems.
• Low FCR: Between 1.0 to 1.3.
• Maintaining the water qualityby the uptake of nitrogen compounds generating in situ microbial protein
• Increasing culture feasibility by reducing feed conversion ratio and a decrease of feed costs
• Plays a powerful role in digestive enzyme secretion and enhance the digestion
• Works as an immunostimulant and stimulate cellular and humoral immunity
• Production costs can be 15 to 20 percent lower compared to conventional system.

• High energy inputs for aerators.
• Power failures over an hour in duration can be critical. Need for back up.
• Biofloc ponds must be lined.
• Technology is more advanced than conventional. Need to train technicians.