Check the conditions of the tank. If the conditions are not up to par correct them. On our bookstore pet home page you will find a link to books and publications to help you with diagnosing these problems. The best prevention is to watch your fish regularly. By doing this you get to know your fish and their habits.
Fish react abnormally during the reproductive cycles.
They may hide more than normal, even tremble and shiver. Check your book for courtship behavior. If your tank has accumulated a high level of harmful substances due to mistakes or even polluted city water, poisoning can occur. Some of the symptoms that arise from this are breathing problems, darting around in the tank, loss of color, and nervousness. If you suspect poisoning immediately change the water.