Recommendations for surface disinfection of salmonid eggs

Article 4.4.1.

Introduction

The practice of disinfecting salmonid eggs at hatcheries is an essential part of ensuring that endemic diseases are not transferred between incubators and between facilities and forms a part of routine hatchery hygiene protocols. The disinfection process is also important when trading salmonid eggs between compartments, zones or countries to prevent the transfer of some pathogenic agents. Although generally effective for disinfection of the egg surface and reproductive fluids, the use of disinfectants will not prevent vertical transmission.

Salmonid eggs may be disinfected with a number of chemical agents. However, the most common method used is disinfection with the iodine-based product, povidine-iodine.

Iodophores, commonly povidone-iodine solutions, have the advantage of providing a neutral pH, being non-irritant and are relatively non-toxic. The neutral pH is important for minimising toxicity and ensuring efficacy. It is recommended to follow manufacturer's instructions to identify circumstances where pH may be a concern. If other iodine based agents are used for disinfection it is essential that they be adequately buffered.

Article 4.4.2.

Disinfection protocol for salmonid eggs

This disinfection protocol may be applied to newly fertilised or eyed salmonid eggs. However newly fertilised eggs should be allowed to commence hardening prior to undergoing the disinfection protocol. Although there is a considerable margin of safety for hardened eggs, the disinfection protocol is not recommended for unfertilised ova or during fertilisation. It is essential that the pH of the iodophore solution is maintained between 6 and 8.

To disinfect salmonid eggs the following protocol should be applied:

1. rinsed in 0.9% pathogen free saline (30-60 seconds) to remove organic matter; then

2. immersed in a iodophore solution containing 100 ppm available iodine for a minimum of 10 minutes. The iodophore solution should be used only once. The ratio of eggs to iodophore solution should be a minimum of 1:4; then

3. rinsed again in 0.9% pathogen free saline for 30-60 seconds; then

4. held in pathogen free water.

All rinsing and disinfection solutions should be prepared using pathogen free water. Iodophore solutions may be buffered using sodium bicarbonate (NaHCO₃) if the pH is low.