Aquaculture Disinfectants: Types and Uses

Disinfection is a common disease management tool for aquaculture sector. It can be both a routine bio-security practice to prevent specific diseases or a routine sanitation process to reduce overall occurrence of diseases that may lower farm productivity. The nature and mode of disinfection greatly varies with the specific reason that leads to disinfection practices. The most commonly practiced approach is chemical treatment in specified doses and for sufficient retention periods to destroy pathogenic organisms that would otherwise access the water systems repetitively.

In aquaculture systems, the threat of cross contamination is prevalent between fauna in the same tank as well as between water holdings, both in fish and crustacean farming. In addition, use of disinfectants is not possible in open systems owing to environmental impacts of chemicals in natural waters and in case of seawater; there is risk of residual oxidant by-products due to chemical reactions with salts in water. Thus disinfectants can be applied safely and most conveniently only to hatcheries and incubation tanks.

Since most aquatic species are highly sensitive to toxic chemicals and the disposal of such waters threatens to contaminate natural water bodies, it is highly needed that a “safe” product be used for disinfection. The term “safe” implies to toxicity tolerance by farm as well as wild aquatic organisms. Thus only a few chemicals can truly adhere to the properties of ideal aquaculture disinfectants in real practice. Some disinfectants are effective against a large range of microorganisms: bacteria, viruses, fungi and parasites. In addition some chemicals are selective biocides to certain strains of exotic eutrophic microalgae. While some disinfectants can work on a short term before the microbes grow resistant to them. Thus the choice of disinfectant and methods of disinfection should be based on the spectrum and ease of application as well.

Requisites of an ideal Disinfectant are summarized herein:

• Should have a wide spectrum antimicrobial activity
• Should not be irritating to aquatic organisms or humans
• Should have minimal toxicity to non target organisms
• Should have high penetrability
• Should be active in presence of Pus and Necrotic Tissue
• Should be non-interfering with normal immunity of fishes
• Should be cost friendly
• Should be non corrosive and non staining
• Should be highly stable
• Should be biodegradable with nil/minimum bioaccumulation potential

Disinfectants can be classified based on their mode of activity as:

1. Oxidizing Agents
2. Reducing agents
3. Detergents

Oxidizing Disinfectants can again be of two types:

1. Those that oxidize without releasing oxygen, most common being Halogen bleachers and Potassium Permanganate and Peracetic Acid
2. Those that oxidize by release of nascent oxygen i.e. Peroxides

They are mostly used to control phytoplankton, pathogens and bottom soil oxidants. Most oxidizing agents are irritant to skin and eyes in high concentrations and except for chlorine, most don’t have long bioaccumulation potential thus non contaminants to food.

Reducing agents consist of organic aldehydes like Formaldehyde and Glutaraldehyde that are popular general disinfectants used as germicide, fungicide or as preservatives in industries. Their main mode of action is by formation of covalent bonds and disruption of functional groups in cellular proteins. They are thus target specific and can be easily applied in selective removal of microbial contaminants. Aldehyde disinfectants are non-irritant, readily biodegradable and do not possess bioaccumulation risks.

Detergents or popularly referred to as Cationic detergents are Quaternary ammonium compounds (Benzalkonium Chloride) that are used I hatcheries to eradicate aquatic insect larvae and nematodes. They are active in disruption of cell membrane and destruction of cytoplasm and cell nuclear material. They are highly active against Gram negative bacteria. There are no known records of reactive products not degrading or chances of bioaccumulation in environment as of yet.

Irrespective of the mode of application and action most aquaculture disinfectants listed above seem to be highly effective in their respective treatment domain but choice of the same lies totally on the users end needs of disinfection and the type of pathogen to be controlled.

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