Aeromonas Alley

“Aeromonas Alley” can be defined as when your pond water temperature ranges between 4°C and 16°C. Between these temperatures, the deadly “Aeromonas/Pseudomonas” (AP) bacteria grow much faster than your fish’s weak immune system. Causing deadly bacterial infections (body sores, ulcers.)

Luther Chien proposed that the koi immune system is designed to keep koi healthy and combat infections with white blood cells playing a key part in the system by attacking or devouring invading bacteria.

The koi immune system is at its most efficient at around 25°C. He said that no white blood cells are found in the koi bloodstream below about 12°C. At these temperatures the metabolism has slowed greatly and the immune system is at its most vulnerable.

Aeromonas bacteria, found in every pond, are not active below about 4°C however, their activity and ability to infect rises rapidly as temperatures increase above 4°C. These bacteria reach their peak activity at about 15 - 16°C.

These bacteria are very influential in freshwater fish farming and often causes disease outbreaks with high mortality rates (80 - 100%) in a short time (1 - 2 weeks). (Rahayu Kusdarwati).

At very low temperatures koi are almost inactive and not feeding but, the Aeromonas bacteria are also inactive, therefore are koi safe from infection.

As the water temperature rises the Aeromonas bacteria become active very quickly and can infect koi simply because our koi’s immune system is still inactive or very weak. The immune system take time to get going again. The increase in the immune activity increases only when the water temperature rises above 12°C - it is literally defenceless against this infection bacterial until the immune system is up and functioning.

This is called the Aeromonas Alley. Weak koi immune system at low temperatures - with a lot of bacterial activity.

The graph below demonstrates the rapid increase bacterial activity as temperatures rise and then the slow catch-up of the koi metabolism (immune system). Added to this our filter bacteria activity also takes time to get going again after winter.

Our thanks to Luther Chien and Syd Mitchell.

This temperature range will always be a potentially risky area - even small numbers of pathogenic bacteria can infect koi and cause infections because they are unable to resist.

When the pond has a high loading of pathogens – uncleaned filters, lots of organic matter, dead algae, dead bacteria then this temperature range will be even more risky.

Added to the Aeromonas Alley are another factors we should build into Spring here in South Africa –

Thunderstorms.

Henry's Law on atmospheric and hydrostatic pressure states that the amount of oxygen which will remain dissolved in a volume of water, at constant temperature, is proportional to the ambient pressure of oxygen gas with which it is in equilibrium.

During a thunderstorm there is a drop in atmospheric pressure. This sudden drop in atmospheric pressure during a storm can release a lot of dissolved oxygen into the atmosphere and rapid de-oxygenation of a pond can occur.

Altitude

Another factor is that at highveld altitudes (1600 meters above sea level) there is about 20% less oxygen that can be dissolved into pond water.

A South Africa Problem

As we have been experiencing power outages for 5 – 7 hours a day - for months - this could contribute to a drop in oxygen levels in our ponds. Especially at night time because the algae is reversing its photosynthesis by taking in oxygen and exhaling carbon di-oxide. Thus, further reducing oxygen levels in the pond.

Perhaps this answers some questions about unexplained koi deaths in spring time in South Africa.