Mystery Goldfish Illness
 

Hi!
I have 2 garden ponds, one 140 Imp gallons, the other 150 Imp gallons. Both established c. 10 years ago with original goldfish healthy & breeding, no previous illnesses. In Spring 2015 I purchased several Shubunkin to add to the genes and give colour variations. Within 6 months total pond death in smaller pond except for 3 Ghost Carp (still totally healthy), 4 diseased survivors in larger. Total loss over 40 fish.

Post mortem and lab testing at Vet revealed nothing apart from slightly congested gills in the specimen fish plus a huge ulcer on back. Some deaths show no obvious cause but most start with red sores, turning to ulcers which grow uncontrollably despite all over the counter remedies, salt baths etc. Vet said pointless to give antibiotics as no virus/infestation/obvious cause found.

Weekly water testing stable and satisfactory, nothing present to contaminate water or filters, ample aeration. It must be something the 'new' fish were carrying which didn't manifest despite 4 weeks quarantine. Anyone come across these symptoms before/got any suggestions?