| Judy . . .
I'm no Koi Health Advisor (KHA), but it's my understanding that normal (healthy and unstressed) koi naturally co-exist with all sorts of harmful bacteria (such as aeromonas) and parasites. The problem occurs when the koi becomes sick/injured/stressed to such a degree that the slime coat can no longer deal with the opportunistic attacks of bacteria/parasites.
Dropsy is not a disease, per se; it is a symptom. As Steve said, "Dropsy is nothing more than the visible signs caused by swelling within the body...fluid retention. The fluid retention can be caused by a number of factors but without those factor(s) being addressed quickly, it will lead to a systemic infection and the death of the Koi." |