It's better when you SAY the joke than when you read it. Although adults may not find this too amusing, your kids and grandkids and nieces and nephews will love it!
What do you call a fish with no eye's (or I's)?
FSH (say fish quickly without the I as a vowle)
What do you call a fish with 10 eyes (or I's)?
FIIIIIIIIIISH (prlong the vowel)