User blog comment:Craftyfirestorm77/Summoner Spells on Fizz/@comment-9463023-20130715203326/@comment-9463023-20130718105736

Yeah, Exhaust is a great spell but not on Fizz.

"Exhaust can give you advantage against an enemy that deals even twice more damage than you do, ignite can't"

Soo... when he deals twice the damage and his damage gets reduced by 30% he still does a lot more damage. Also, the point of taking ignite is to maximize damage early and to help you in snowballing, so that you are the one who deals twice more damage than the enemy.

It's really hard to escape from Fizz and unless he's a failer, who uses Ignite but can't do it properly (which seems to be your assumption), Exhaust is not that good on him. You don't need it to chase, don't really need it to duel.

Lategame Fizz can instagib the enemy adc and if your support runs exhaust he can cast it on their midder. If there's an exhaust in your team already, there is absolutely no point in taking it yourself.

At least that's my opinion.