Shellfish Breeding and Hatchery Management (2+1)

25.2.2.2 Chemical Methods of Disinfection

i) Chlorination

It is commonly used method for disinfection of water in shellfish hatcheries. The water is treated with 0.2-0.5 mg Cl₂/litre of water for 20 to 30 minutes. The removal of residual chlorine prior to introducing the disinfected water into shellfish hatchery is inevitable. Vigorous aeration was given to remove the residual Chlorine present in water or it is passed over charcoal for removal of chlorine. If any chlorine residue is present in treated water, it is toxic to shellfishes. Chlorine in the form of calcium and sodium hypochlorites and chloramines are commonly used. Nowadays chlorine-dioxide is also used as disinfectant, which is considered as safe as it seldom leaves any residual chlorine in harmful form.

ii) Ozonation

Electric discharge and UV radiation of a suitable wavelength produce a 3-atom form of Oxygen (Ozone). The contact concentration of Ozone is around 3 mg/ liter of water with residuals of below 0.15 mg/ liter. The residual ozone may also be removed with charcoal prior to use. However, the cost of equipment and use is relatively high.

iii) Formalin and Formaldehyde

Formalin water containing dissolved Formaldehyde is a readily available industrial Chemical. A 1:100 mixture of formalin and water is used to disinfect the water. Formaldehyde [HCHO] gas has been used for the disinfection of sealed building, usually generated by heating Para formaldehyde and the polymerized solid of Formaldehyde. It is effective against many viruses and bacteria.

iv) Quaternary Ammonium Compounds [QAC]

QAC are widely available in numerous brands and strengths. The active concentration is approximately 1200 mg/ liter (1200 ppm) of water. It is effective against gram +ve bacteria, some viruses but less effective on fungi and gram -ve bacteria.

v) Hydrogen Peroxide:

It is clear colorless, water like in appearance, has pungent odour, and do not highly corrosive or dangerous toxic effect.

vi) Iodophores

Iodophores are generally available at 1% solution. They are organic compounds that release free iodine. The active concentration for disinfection of water is 50 mg/ liter and for equipments 250 mg/ liter. It effectively disinfects bacteria and some viruses.

During unfavourable and lean demand periods have to be advantageously utilized for the purpose of disinfecting the entire shellfish hatchery.