Is Fizz ult supposed to bypass Sivir's spell shield?

It's a weird thing. What your SS blocks is the attachment, but it doens't stop the shark. I assume Fizz's Ult is like Vi's dunk - once it's off, it's going.

Just shield the chum, it's got a slow missile speed.

If your spell shield is up when he throws the fish at you it won't attach to you but it lays on the ground so you could walk back over it and reattach to you though.

That's when you do Sivir and Morgana.

Once Sivir's spell shield dissipates, Morgana casts her's on Sivir.

thats cause delayed effects that are attacjed to you aren't affected by spellshield(BV shouldn't work aswell). You can prevent his ult from attaching to you in first palce with your spellshield, but once it's at you, you'll eat it(or, well, it'll eat you) Same with zileans bombs or Zeds deathmark, you can spellshield them befor to prevent the bomb(mark form getting placed on you. but once you have it, there is nothing you can do.