Disinfection in Aquaculture: Eggs, Equipment and Facilities
How disinfection breaks disease cycles in aquaculture — salmonid egg surface disinfection with iodophor, equipment and footbath disinfectants, and the limits and safety of each.
Overview
Disinfection breaks disease transmission cycles in aquaculture by removing or killing pathogens on eggs, equipment, vehicles and surfaces. It is a core part of biosecurity, used alongside quarantine, vaccination and good husbandry. Disinfectant efficacy depends on the right concentration, an adequate contact time and a low organic load, because organic matter consumes and weakens many disinfectants.
Egg disinfection
Surface disinfection of fertilized eggs prevents pathogens being carried between incubators, facilities and countries. The most common method for salmonid eggs is an iodine-based product (povidone-iodine, an iodophore), which is near-neutral in pH, non-irritant and relatively non-toxic. The WOAH Aquatic Animal Health Code protocol is summarized below.
| Step | Detail (WOAH) | Note |
|---|---|---|
| 1. Pre-rinse | Pathogen-free 0.9 to 1.1% saline, 30 to 60 seconds | Removes organic matter |
| 2. Disinfect | Iodophore solution with 100 ppm available iodine for a minimum of 10 minutes | Egg-to-iodophore ratio max 1:4; pH kept 6 to 8 |
| 3. Post-rinse | Pathogen-free 0.9 to 1.1% saline, 30 to 60 seconds | Removes residual iodine |
| 4. Hold | Pathogen-free water | Buffer iodophore with sodium bicarbonate if pH is low |
WOAH notes this protocol may be applied to newly fertilized (after water-hardening) or eyed eggs, but not to unfertilized ova or during fertilization. Crucially, while it is effective on the egg surface and reproductive fluids, surface disinfection will not prevent vertical transmission of pathogens already inside the egg, such as the agents of bacterial kidney disease and infectious pancreatic necrosis.
Equipment, footbaths and facilities
Nets, siphons, tanks and vehicles are disinfected to stop pathogen spread within a farm, and footbaths are placed at entrances and exits of system rooms, hatcheries and quarantine areas. UF/IFAS describes several options with important safety caveats.
- Chlorine — effective but destroys nets and must be neutralized or rinsed off thoroughly to avoid killing fish.
- Iodine-containing compounds — equipment must be rinsed before use because they can be toxic to fish.
- Quaternary ammonium compounds (e.g. benzalkonium chloride) — commonly used but toxic to fish, so must be rinsed adequately before reuse.
- Virkon Aquatic (a peroxygen product) — used by many facilities and shown to be safe and effective against a wide range of aquatic pathogens when used as directed.
- UV radiation and ozone — used to disinfect the water in recirculating systems.
Ponds and water
Earthen ponds are commonly disinfected between cycles by draining, drying and applying agricultural lime, which raises pH and helps inactivate pathogens. Water entering or recirculating in intensive systems can be treated with UV or ozone. As with all disinfection, follow label rates and ensure any chemical is fully removed or inactivated before fish are returned.