see the associated article "Choosing the right egg disinfectant"

With more and more emphasis on biosecurity, the latest buzzword around many fish culture facilities is disinfection. Disinfection protocols are now part of the daily routine for much of the aquaculture industry. But what is disinfection? What are disinfectants? And what is the best way to select a disinfectant? Disinfection and disinfectants may be defined as follows:

These definitions loosely describe what the fish farmers hope to accomplish. More accurately, they want to rid their sites of any harmful disease-causing organism: viral, bacterial, or otherwise. Therefore, it is important to look for products that are not only cost effective but will work in a specific application under specific conditions.

There are many questions that need to be answered before committing to a disinfection product or procedure. These include: How much organic matter is present? Will live animals be in contact with the solution or its residues? What is the required contact time? What pathogens are being targeted? How will the product be applied? And, how is the cost effectiveness measured?

How much organic matter is present? The amount of organic matter (feed, feces, and slime) on the equipment, surfaces, or in the disinfection solution will greatly affect the success of the product. If there are high levels of organic matter present, specially formulated products containing surfactants, detergents, acids, and buffers, or some combination of these, may be appropriate. On the other hand, if the surfaces are clean and there are low levels of organic matter, less complex disinfectants may be adequate.

Will live animals be in contact with the solution or its residues? Certain disinfectants can be used to disinfect live fish and eggs. Iodine (PVPI) based products have been used extensively for disinfecting eggs before they are placed in incubation units. Chloramine-T has also been used to disinfect fish eggs. However, it is more commonly used to combat bacterial gill disease in many fish species.

What is the contact time? Many disinfectants are quite effective but require a long contact time (30 minutes or more) to be effective. Other disinfectants are specially formulated to be fast acting and are effective within 10 minutes or less. Some peroxymonosulfate-based products have even been proven effective within 30 seconds in footbath applications. The amount of time available for cleaning a surface is very important and may sometimes dictate which disinfectant product is used.

What pathogens are being targeted? Some disinfectants target specific organisms or specific groups of organisms like bacteria, fungus, or viruses. If there are known disease-causing organisms that should be targeted, disinfectants should be selected based on its effectiveness against that bug. If the threat is unknown and general-purpose disinfection is required, a high quality, broad-spectrum disinfectant may be a better choice.

How will the product be applied? The application method can help determine which product is better suited for a specific application. It is important to know that the product is compatible with the existing equipment and that there are no serious worker safety concerns. A disinfectant may not be cost effective if special handling equipment is required.

How is the cost effectiveness measured? To measure cost efficacy it is important to first determine how much the product costs in terms of dollars per liter of active solution. That way, a fair comparison can be made among all existing products. It is also important to find out how long the solution will last. If a footbath, for example, has to be changed two or three times a week for a cheaper product and only once a week for a higher quality product, the actual cost for using those products may be the same. Finally, it is important to know how many of the previously discussed criteria are being met. A product may be cheap to purchase but may require long contact time, high concentrations, or high levels of rinsing to remove harmful residues. In this case, the time and labour costs may outweigh the product costs.

There are probably more disinfectants than there are situations that require disinfection. Selecting a proper disinfectant for a fish farm facility is a little more complicated than going to the local grocery or janitorial supply store and picking up a can of Lysol. Many factors including the surface type, pathogen load, organic load, and contact time must be considered. In addition, it is important to know that the disinfectant selected is going to be effective against the pathogens that are likely found on the farm. A little research, and help from your local supplier, should make the job of selecting effective disinfectants easier.