Sometime Fish Get Sick

Let me start by saying I have never (knock on wood) killed a complete stock of fish. However, occasionally things happen and I have lost a few. Most illness in fish is brought on by stress and poor water quality. It is important that when one will be handling the fish the water quality should be kept as good as possible and all other stress factors be minimized. This is especially important to catfish with their sensitive skin and scardy cat nature.

This first picture is of some catfish that were kept in a quarantine system that was too small I believe. The flow rate and water quality along with the confined tank was just not good enough and they fish started getting white patches on them which progressed to exposed flesh and eventually the fish would die. I’ve only ever lost one catfish to this in a larger tank but it has been a problem in any of my smaller quarantine systems. I now no longer intend to put any catfish more than about 6 inches into anything smaller than a 300 gallon tank even if it is only temporary quarantine. Tiny catfish seem fine in small tanks but as they grow out, there definitely needs to be more space.

These fish seem to have died of a different disease but it could have been due to over feeding during very hot weather, however I noticed an injury on one that may have provided a vector for the illness to attack. Generally as the weather warms up, the fish will eat more but once the water gets up past the peak temperature the dissolved oxygen levels that the water can hold start to drop below a level at which the fish can remain happy when there is a heavy oxygen demand on the water. So there is a point at which feeding should back off a bit as the water moves to the “hot” range for the fish.

What to do when sick fish are noticed. First make sure water is flowing well, nothing is clogged and there is plenty of aeration. If the sick fish is easy to catch and remove, go for it but I wouldn’t stress out the whole tank trying to catch a still active fish. Instead, do some water tests to see if you can figure out what is wrong and make sure there isn’t an accumulation of solids in the system that might be causing issues. Look around for anything amiss, remove dead fish and reduce feed if there is any indication of poor water quality. Observe fish carefully especially at feedings and adjust accordingly.

A single dead fish does not necessarily mean there is a problem with the system but it should cause one to run tests and check things carefully. If many fish die or if a steady string of dead fish happen, it is definitely a sign of something wrong.