It surely would not be good for the fish, don't get me wrong. But if you put a damsel (for ex) in a new tank and cycle (as they did back in the dark ages) you can get readings this high and they will often survive. The biggest factor is how quick it changes - dropping from a bag straight in to a tank with this level is more shocking than putting one in a tank that ramped itself up over 3 days.
Pls understand I in no way condone or encourage this. - During my initial shipment of pacific LR
stayed at 7.0 for 10 days and many of the hitchhiking inverts survived.
tried to sell me damsels during that cycle, when I said no it'll stress the fish they stated "they'll be fine, and it will speed things up
Just my 2c.
Please explain this. I was thinking that ammonia that high would have the fish showing signs of problems at the very least. I figured he'd be swimming upside down.