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Top 5 Chemicals for Mud Crab Recirculating Aquaculture Systems | Aquaculture Technology

Recirculating aquaculture systems are designed to recycle the amount of water used, and to ensure that the water is of good quality via a series of filtration systems. Proper usage of chemicals to ensure excellent water quality is paramount to the success of your recirculating aquaculture system. In this post, we will be touching on the top 5 chemicals that you will need to have in your farms running on recirculating aquaculture systems.

#01 Sea Salt or Treated Seawater

Mud crabs proliferate in brackish water environment, and your recirculating aquaculture systems need to replicate the environment in which your crabs are from. Maintaining proper salinity for the culture of mud crabs is important to ensure good growth of the crabs, more on the salinity here. There are a few options to obtain good quantities of brackish water. You can opt to make your own seawater by mixing high-quality sea-salt with the municipal water supply. Other options also include using treated seawater as a source of salinity, where you dilute the seawater to the required concentration. Quality of sea salt varies greatly between sources, and you should be careful in applying sea-salt with unknown origins. In many cases, biofilters are incorporated into recirculating aquaculture systems to bring down water or salt usage by treating the water, more on biofilters here.

#02 Sodium Thiosulphate

Operators that are planning to rely on the municipal water supply will need to remove the chlorine in the water. Chlorine removal is also needed for those who plan to disinfect their water with chlorine. The ideal anti-chlorine agent that are commonly used in recirculating aquaculture systems is sodium thiosulphate. While chlorine can be removed in several hours by the exposure to sunlight, it may take weeks for chloramines to completely break down. Hence, it might be more economical to use the relatively inexpensive sodium thiosulphate as an anti-chlorine agent. Residual chlorine in the recirculating aquaculture system will not only affect the mud crabs, but also impact the bacteria responsible for biofiltration.

#03 Sodium Bicarbonate

Maintaining pH and alkalinity is crucial for any recirculating aquaculture systems. pH refers to the acidity of the water, and should be kept in the range between 7-8. A drop in pH affects the crabs and the biofiltration process. To maintain the pH in the system, carbonate sources needs to be added into the water. One of the good ways to maintain pH in recirculating aquaculture systems are with the addition of sodium bicarbonate or commonly known as baking soda. Although lime is commonly used in earthen ponds, sodium bicarbonate is the preferred option in a recirculating aquaculture system. This is due to their ease to dissolve in water as compared to lime.

#04 Dolomite

Apart from the pH and alkalinity, important minerals like calcium, magnesium and trace elements get depleted over time. Upon depletion of minerals, farms operators can either opt to replace the culture water with fresh seawater or newly made artificial seawater from sea-salt. However, some operators prefer to add in the necessary minerals with the addition of dolomite. Dolomite differs from lime, dolomite contains some amount of Magnesium that is required for healthy growth for crabs. Dolomite remains the first option for mineral addition due to their inexpensive nature, occasionally operators will opt for calcium chloride or magnesium chloride to supplement the minerals they are lacking.

#05 Disinfectant Potassium Permanganate (KMnO4), Iodine or Sodium Hypochlorite

To avoid diseases spreading in your system, it is crucial to ensure that animals are properly quarantined and disinfected before putting them into your recirculating aquaculture system. Chemicals used to disinfect the animals needs to be applied using the correct dosage to avoid stress to the crabs. In Malaysia, we use potassium permanganate to disinfect the crabs. In countries like the Philippines where potassium permanganate is prohibited, aquaculturist will have to opt for other options like povidone-iodine or formalin. Apart from disinfecting the animals before placing them in recirculating aquaculture systems, farm operators also disinfect the boxes and the pipings after each harvest. This is to make sure harmful pathogens do not have the opportunity to build up in the recirculating aquaculture system over time. For the equipment, the typical disinfecting agent used is sodium hypochlorite or commonly known as bleach. Equipment disinfected needs to be fully dried before reuse.

In short, proper and responsible usage of chemicals in recirculating aquaculture systems is needed to ensure successful operations and products that are fit for human consumption. While most of the equipment is readily off the shelf, one should attempt to source from reputable aquaculture chemical suppliers to obtain the best pricing.

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