Shellfish Breeding and Hatchery Management (2+1)

24.1.2 Removal of dissolved solids and gases

The culture tank water has dissolved solids arising due to the excretion of the fishes and dissociation of various compounds from the organic matter due to bacterial decomposition. The particles may vary in size from 10^-6 to 10^-4mm which can not be filtered by the mechanical filter. Therefore classical or biological treatment is recommended.

Chemical treatment is done through precipitation method, which is not recommended for the shellfish hatchery tank water. Biological treatment in bio filter is the only option to remove the dissolved gases and compounds in the water.

Water in the hatchery tanks will have high amount of nitrogenous wastes and ammonia in the diet and gaseous compounds in the water. Carbon-di-oxide and hydrogen sulphide are other major gases present in the water and nitrogen and sulphur along with other minerals may be other significant matter present in the water.

Biological filtration will help in removing the gases by the process called nitrification with the help of nitrifiers. The bio media used inside the biofilters will provide the space for the living of the Nitrosomonas and Nitrobacter. These microbes will use the nitrogenous wastes in the water and convert them as harmless Nitrates. This process is highly useful for the hatcheries in maintaining the water quality in the hatchery tanks.