Introduction shrimp farming in Biofloc system
Biofloc farming is a technique of enhancing water quality in aquaculture through balancing carbon and nitrogen in the system. The main principle of the Biofloc technique is the generation of nitrogen cycle by maintaining a higher C: N ratio through stimulating heterotrophic microbial growth, which assimilates the nitrogenous waste that can be exploited by the shrimp cultured spices as a feed. The Biofloc system is not only effective in treating the waste but also grants nutrition to the aquatic animal.
A step by step guide to Biofloc shrimp farming
The higher C: N ratio is maintained through the addition of carbohydrate source and the water quality is improved through the production of high-quality single-cell microbial protein. In such conditions, dense microorganisms develop and function both as bioreactor controlling water quality and then protein food source. The Biofloc technology in shrimp farming implemented due to its bottom-dwelling habit and resistance to environmental changes. An improved breeding performance observed in shrimp reared in the Biofloc system when compared to that of normal cultural practices.
Biofloc farming has become a popular technology in the farming of Pacific white shrimp. In addition to the conventional biofilter systems, the Biofloc technology (BFT) is recently proposed as an alternative solution for wastewater treatment and feed re-utilization, yet it is not suitable for small farms due to intensive aeration, regular waste removal and requirement of additional carbon source to stimulate heterotrophic bacteria growth. Biofloc technology is a technique of enhancing water quality through the addition of carbon sources to the aquaculture system contained in the feed or external carbon sources. This can minimize water exchange and water usage in aquaculture systems by maintaining adequate water quality within the culture unit. Biofloc systems support nitrogen removal when the organic matter and biological oxygen demand of the water system are high. Biofloc technology is composed of a variety of microorganisms, uneaten feed, feces, detritus, and suspended particles with water propulsion and aeration.
Principle of Biofloc shrimp farming
In a typical brackish water pond, only 20–25% of fed protein is utilized by the shrimp, the rest of which goes as waste in the form of nitrogenous metabolites. Manipulation of carbon: nitrogen ratio in shrimp ponds encourages the uptake of this inorganic nitrogen into a microbial protein known as Biofloc. Biofloc farming combines the removal of nutrients from the water with the production of microbial biomass, which can be used by the cultured species, in situ as an additional food source. Then, the C: N ratio in an aquaculture system can be maintained by adding different locally available cheap carbon sources and reducing protein percentage in the feed. Under optimum C: N inorganic nitrogen is immobilized into the bacterial cell while organic substrates are metabolized.
Advantages of Biofloc technology for shrimp farming
- The advantages of Biofloc technology include high biosecurity.
- Production and carrying capacity are 5 to 10 percent higher than in typical culture systems, with zero water exchange. Shrimp grow larger and reflect feed-conversion rations between 1.0 to 1.3 and production costs can be 15 to 20 percent lower.
- Eco-friendly culture system
- It reduces environmental impact
- Improves land and water use efficiency
- Limited or zero water exchange
- Higher productivity
- Higher biosecurity
- Reduces water pollution and the risk of introduction and spread of pathogens
- Cost-effective feed production
- It reduces the utilization of protein-rich feed and also cost of standard feed
- Biofloc reduces the pressure on capture fisheries, that means, use of cheaper food fish and trash fish for fish feed formulation
Disadvantages of Biofloc system
The disadvantages of Biofloc include high energy inputs for aerators. Power failures over an hour in duration can be critical and Biofloc ponds must be lined. The advanced technology also demands a greater need for properly trained technicians.
Requirements for Biofloc shrimp technology
Biofloc systems reduce the spread and effectiveness of pathogens as simultaneously improving shrimp health through better water quality. As such, Biofloc can give us a natural way of producing more seafood sustainably, while concurrently improving farm profitability. Biosecurity is a priority in aquaculture production. For example, in shrimp farming, the impact of disease outbreaks during the past two decades greatly affected the operational management of shrimp farms worldwide. Biofloc technology brings an obvious advantage of minimizing the consumption and release of water, recycling in nutrients, and organic matter. Also, the pathogen introduction is reduced, improving the farm biosecurity.
Biofloc farming technology will enable aquaculture to grow towards an environmentally friendly approach. Consumption of microorganisms in BFT reduces Feed Conversion Ratio (FCR) and consequently costs in the feed. Also, the microbial community can rapidly utilize dissolved nitrogen leached from shrimp feces and uneaten food and then convert it into microbial protein. These qualities make a minimal-exchange Biofloc system an alternative to extensive aquaculture. Microorganisms in Biofloc might partially replace protein content in diets and decrease its dependence on fishmeal.
Biofloc is defined as macro aggregates composed of diatoms, macroalgae, fecal pellets, exoskeleton, and remains of dead organisms, bacteria, and invertebrates. And, this microbial protein may have higher availability than feed protein.
The requirements for Biofloc system operation have a high stocking density of about 130 to 150 PL10/m2 (10 post larvae (PLs) per square meter) and high aeration of 28 to 32 horsepower per hectare (hp/ha) with correct paddlewheel position in ponds. Ponds should be lined with concrete or high-density polyethylene (HDPE), and pelleted grain and molasses are added to the culture water. Shrimp production of 20 to 25 metric tons per hectare (MT/ha) per crop is normal for Biofloc systems. And a maximum production of nearly 50 MT/ha was achieved in small ponds.
Biofloc farming systems remove metabolic wastes from aquatic production systems. Then, they replace biofilters in a classic clear water Recirculating Aquaculture System (RAS). Bacteria that convert ammonia into nitrate are cultured in the main rearing tank as opposed to in a separate vessel. The bacteria form aggregates or Bioflocs suspended in the water column. This is done for many reasons. Eliminating the biofilter reduces costs and then saves floor space. In the case of shrimp, the Biofloc becomes an additional feed source, which decreases the feed conversion ratio or FCR of commercial feeds, again reducing costs.
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Commercial interest in Biofloc shrimp farming technology
Commercial interest in Biofloc technology is threefold, for Bioflocs gives high productivity, low feed-conversion ratios, and a stable culture environment. And, with emerging viral problems and rising costs for energy, Biofloc technology appears to be an answer for sustainable production at a lower cost.
Biofloc technology has not only been applied at commercial shrimp grow-out farms but also in super-intensive raceways to produce more than 9 kg shrimp/m3. The raceway applications have supported nursery and then grow-out to shrimp broodstock rearing and selection of family lines.
Biofloc management for shrimp farming
The Biofloc in the shrimp-rearing tank must be considered a dynamic living organism and must be managed as such. The main component of Biofloc is heterotrophic bacteria. The function of the Biofloc system is to reduce the nitrogenous metabolic waste (ammonia, nitrite) produced by shrimp feeding and production. It is assumed that a 35 percent crude protein or 5.6 percent nitrogen feed is applied at 400 kg/day in a 10,000-cubic-meter, shrimp Biofloc system with an FCR of 1.3.
Ammonia consumed by heterotrophic bacteria becomes protein, which can be consumed by shrimp and converted into growth. Heterotrophic bacteria require carbon for ammonia to be assimilated. In addition to the commercial feed, a supplemental source of carbon should be added to stimulate the production of the heterotrophic bacteria and reduce the nitrogenous waste.
Shrimp feed has a carbon to nitrogen (C: N) ratio of about 7-10:1. Heterotrophic bacteria would prefer a ratio of about 12-15:1. Simple sugars or starches are added to increase the ratio and promote bacterial growth. Additives have included molasses, sugar, sucrose, and dextrose and some producers use glycerin. The simpler the sugar, the quicker is the response from the bacteria and application rates will vary with the protein content of the feed and composition of the carbon source, but a good rule of thumb is that for every 1 kg of feed, about 0.5 to 1 kg of carbon source is required. Higher protein feed will require higher carbon supplementation. Actual applications should take into consideration the levels of ammonia and nitrites in the water.
The choice of carbon source is mainly dependent on price, availability, ease of application, and efficacy. The carbon source must be diluted before application no matter the physical state. Oxygen additions can be combined with the need to keep Biofloc in suspension. Without mixing, heterotrophic bacteria colonies will sink and then lose the ability to remove ammonia. Mixing is accomplished with the same devices that add oxygen, namely airlifts, diffuser stones, and water pumps. The choice of aeration or oxygenation methods depends on the production level and centralization of equipment. High production levels can require the use of pure oxygen supplementation. Use of low-pressure, high-volume air blowers can be sized to cover the needs of multiple tanks driving airlifts and diffusers. Likewise, water pumps can drive multiple venturi aspirators but are sized for individual large tanks.
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Physicochemical properties of Biofloc shrimp farming
The optimum water temperature for shrimp culture in the Biofloc system was reported between 25°C to 31°C. This is important as temperature range can influence shrimp metabolism, feeding rate, oxygen consumption as well as survival and tolerance towards toxic metabolites. That low temperature can influence the outbreak of White Spot Syndrome Virus (WSSV) in shrimps as a sudden change in temperature affects the shrimp’s immune system.
The optimum salinity for shrimp farming was between 15 to 25 ppt. Salinity is mainly dependent on the amount of rainfall and the rate of evaporation. Less quantity of rainfall and high evaporation rate contributed to high salinity in shrimp pond.
pH value refers to the degree of alkalinity or acidity in the water sample. pH is crucial for the survival and growth of shrimp culture as it affects metabolism and another physiological process of shrimps. The ideal pH level for shrimps culture was between 6.8 to 8.7. Low pH value in shrimp ponds has been reported as the cause for infection of White Spot Syndrome Virus (WSSV) in shrimps.
Setting-up Biofloc facilities for shrimp
Pre-treatment of pumped seawater was prepared following standard operation process (SOP) developed by shrimp farmer (For example; holding water, filtration, fertilized water, etc.). Prior stocking of shrimp post-larvae (PL), two super-intensive 2-phase Biofloc shrimp ponds consist of nursery and grow-out ponds lined with High-Density Polyethylene (HDPE) constructed for setting-up the Biofloc facilities. These ponds were set up with optimized designs and positions of paddle wheel to maximize the flow rates for Biofloc technology formation while enhancing shrimp growth performance. As the bio-security features are improved, concurrently, it allows super-intensive farming with a stocking density of up to 350 post-larvae per meter square were practiced. This can compensate for the additional cost spent on the development of the new system.
Formulated conditions for Biofloc shrimp farming
The Biofloc system biomass was obtained after allowing the water to be completely settled for half an hour. The volume of formed Biofloc was controlling between 4 to 8mL/L by the daily addition of molasses to obtain maximal growth of Biofloc while maintaining water quality and shrimp productivity.
Similarly to Biofloc sampling, measurements of water quality parameters including temperature, pH level, salinity (ppt), dissolved oxygen (DO), nitrite, orthophosphate, and ammonium were measured during each sampling date. The monitoring of temperature, pH, salinity, dissolved oxygen was measured using a multi-parameter probe. On the other hand, nitrite, orthophosphate, and ammonium were analyzed following the standard method for Examination of Water and Wastewater using diazotization, ascorbic acid, and phenate method, respectively. The occurrence of potential disease in both pond water and shrimp culture determined by randomly sampled water and shrimps from each pond.
The important parameter that needs to be controlled during the implementation of Biofloc technology is the ratio between carbon (C) and nitrogen (N). The C/N ratio of 15 was controlled through the addition of commercialized molasses as carbon sources. To calculate C/N ratio, protein percentage in the formulated feeds which have nitrogen and carbon was first identified. For example, 35% of feeds containing protein and daily addition of 630 grams of molasses to maintain a C/N ratio of 15 throughout culture periods.
Shrimp stocking and feeding in Biofloc shrimp farming
Shrimp are stocked in Biofloc farming systems at densities ranging from 250 to 500 post-larvae (PLs) per square meter. Production for these systems ranges from 3 to 7 kg/m² and/ or 3–9 kg/m³. Feed conversions range from 1.2:1 to 1.6:1. Microbial proteins in the Biofloc add 0.25–0.5 additional growth units for every one unit of commercial feed.
Shrimp are stocked in single batches of like-size post larvae (PLs) and feeding is based on calculations of biomass, feed conversion, mortality, weekly gain per individual, and percentage body weight feeding. Feed rate in shrimp is adjusted after routine sampling for uneaten feed on the bottom of the tank using a dip net one-half hour after feeding. Less than optimum water quality parameters can be an indicator that feeds are less than optimum. The feed can be dispersed by hand or with a mechanical device such as a belt feeder. Feeding by hand is best for dispersing the feed over a wide area of the tank allowing all individuals to get food. Automated feeders can be used when the operator is not present and processed feed is still the most important addition for good growth of shrimp even in a Biofloc system. Shrimp feed must be purchased from a reputable manufacturer and stored properly. Diets change over the production cycle with pellet size increasing from about 1.5 mm up to 2.5 mm as the shrimp mature.
Different shrimp species for Biofloc system
Nursery rearing of penaeid shrimps enhances the growth and survival of shrimps in grow-out systems. Biofloc technology has been applied successfully in the nursery phase in different shrimp species such as L. vannamei, P. monodon, and F. setiferus. Bio-floc and periphyton based nursery systems result in increases of 30 to 50% in weight and almost 60 to 80% in final biomass in shrimp at the early post-larval stage when compared to conventional clear-water system. Other advantages contain better health and increased immunity through the continuous consumption of Biofloc which in turn positively influences grow-out performance. In a trial in India, the weight of the shrimp post-larvae or juveniles was enhanced from 15 to 250mg with rearing densities above10,000/m3 of water showing better performance in the Biofloc system for P. monodon and F. indicus.
Recirculating shrimp nursery systems with the use of Biofloc shows promising results and reduces the size and cost of the filtration system. It is reported that Biofloc also can reduce the costs for standard starter feed up to 50% without compromising the growth, health, and survival of the animals. The Biofloc system based nursery can improve the optimization of farm facilities with high stocking density in the nursery phase along with ensuring the successful cross over from early mortalities.
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