Anyone else feeding live cicadas to their fish? They're everywhere here in Maryland and my fish love them.
I fed a lot of grasshoppers, crickets and other large bugs to my fish when I kept monsters. I always collected them around my house and never used any kind of insecticides or other pesticides on my rural acreage, so felt they were pretty safe to use.
Cicadas can fly a considerable distance after they emerge as adults; I would give some thought to the possibility that they came in contact with some chemical agents at another location before you catch them.