Betta Mass Death

[knightshawk]

after keeping bettas for quite some time i recently had an outbreak of an unknown (to me) disease that wiped out all my female stock in one tank. The symptoms appear to be fairly large black and purple brusies in the vicinity of the head, there is no consisentcy in their placement although many appear below and behind the gills, death occures within hours, it is not attack , the only other fish in the tank are two small cory cats and a small pleco,which are unaffected,after the tank was wiped out i waited and placed a test female in it with the same results within 24 hr..i can find no info anywhere relating to the symptoms, tried treatment with both Maracyn one and two, still loosing everything i put in the tank, tried a complete water change ,waited 2 days with same results, does anyone have any info at all ???

 

[Colin_T]

Black patching on fish is usually bruising (or the equivalent of) and is often associated with chemical poisoning, possibly too much chlorine from a big water change. However, the catfish should have problems if this was the case.
The other option is a virus that has infected their brain and skull area and that has caused inflammation and bruising but it would be unlikely to kill all the bettas within a short time.
They might have suffocated. That would cause rapid death and the gills to become purple or darker than normal. The labyrinth organ is in the head and might have been affected. If the surface has an oily film across it the fish would be unable to take air in properly and could have died from too much CO2 in the system.