Self-poisoning in Corys

[Paul_fox]

Self-poisoning in Corydoradinae Catfishes

How many of you have purchased a group of new long sought-after Corys, only to find that they have all died in the bag on the way home. I know I have in the past, but not any more. So why does this happen? Well, from my observations, I have discovered that many - if not all - Corydoradinae catfish give off a toxic substance, the strength of the substance also seems to vary according to species.

I believe this to be a natural defensive mechanism, primarily against predation, which is released when the Cory is grabbed by a larger predator, hopefully causing the predator to release its grip and affording the Cory a chance to escape.

Putting this theory into hobby terms, we the aquarist being the predator, catch the Cory in our net and put it into a bag or small container. The Cory naturally is put under stress and instinctively releases its toxic fluid. Here we come to a slightly different situation for the Cory, although it has been released from the net it is still in shock and in the confines of a very small space it cannot escape from the poisonous toxins it has released, in a very short space of time the Cory quickly starts to be affected by the poisonous fluids that have now fully dispersed into the water. The effect on the Cory is such that it seams to stop breathing, and literally within minutes, the Cory is dead. So far I have been unable to isolate the substance and only one image of its release is known (fig 1).

This problem can and does happen whenever we transport Corys, be they new fish from a shop, a group of young you are taking to a friend or a shop to sell or even a single specimen fish you wish to exhibit at a show. The first indication we have of the problem is slight foaming at the surface of the water in the bag or container and the Cory(s) may be breathing rapidly, although it is usually the opposite and their breathing slows down.
As long as a few basic procedures are followed, it is quite a simple matter to avoid losing Corys through self-poisoning.

The first thing to do when catching your Cory(s) is to take enough water for transporting the fish from the host tank and put it into a container. Then take another larger container, also containing host tank water, catch the Cory/s and put them into the second larger container, now disturb the Cory/s a few times over the next few minutes. This should create the necessary amount of stress to ensure that they release their toxins. The Cory/s should then be removed from the second container and placed into a bag containing water from the first container; the water from the second container should then be discarded.

A further tip is when buying Corys is to try and ensure that they are stressed enough by the person catching them, to ensure they have released their toxin before they are put into the bag. Sometimes it is the inexperienced shop assistant that is the best person to catch your new Corys, mainly because they tend to chase them around a little more creating that extra little bit of stress.

The first sign of a problem will be small bubbles on the surface of the water and may be even a little yellowing of the water.




All words and photo are copyright to Ian Fuller