Hi guys
need some help. My smallest (and weakest) koi died this evening. He was always very timid and ate little getting frightened by the others, he didn't grow anywhere near as much as the others who came in approx. the same size / time. I noticed last night he was lethargic to an extent, but as he always hides and I have the covers on the pond - it was difficult to see. This evening I saw he was barely moving and whilst I started getting my hospital tank ready - he died.
I'm worried that it may spread to the others, so I've got some pics and if anyone can advise on likely cause of death, it would be helpful. Pics below, also his body was a bit bloated looking before he died and there was also a very small red circle just behind his head and you can see the redness on his gill plates.