One of the strongest parts about Modern fish is the colors. The fact that you have U/W means you have access to one of the most annoying creatures in the format: Meddling Mage . I'd throw at least 3x in sideboard to stop so many things. He can also be cheated out via AEther Vial if you leave it at 2.

Meddling Mage is a MUST for the SB. Thanks for the suggestion!

That's why I mainboard AEther Spellbomb in my eggs deck...

what about some more card draw? Sygg, River Cutthroat ?

Phantasmal Image is also pretty awesome in a merfolk deck.

Mutavault is pretty much a given.

if you could get some fetch lands and have less non island lands Vedalken Shackles is a great control element.

Mutavault is a great card, but I'm not dropping the coin for it. Phantasmal Image is definitely a card I'm trying to squeeze in. Thanks for the suggestions

Phantasmal Image is definitely a card you want in at least your SB (he not only helps you, but can get rid of things like Emrakul, the Aeons Torn .

Also, because you run so many fish, card:Aquitect's Will should be considered over Spreading Seas . It's a merfolk card so you get to untap things from Merrow Reejerey , it places a counter on the card so enchantment hate won't get rid of your islandwalk, and it only costs 1 mana.

Another SB card you may want to consider is card:Hurkyl's Recall and/or Echoing Truth for match-ups against robots and Splinter Twin .

Here's a mono-blue fish deck I made a while ago that had some pretty good match-ups (it just got too boring for me) : Starting to like Fish

card:Aquitect's Will definitely seems like a better card over Spreading Seas , however, the latter makes the land and Island. Period. Very helpful against the likes of Tron or any other multicolor deck that doesn't run blue. That can really help to slow your opponent down long enough to cram enough Merfolk down their throat for the win.

card:Hurkyl's Recall and Echoing Truth will definitely find spots in my SB. Thanks for your suggestions.

There isn't much, if any, enchantment hate that people actually run in Modern. (Hence why card:Quest for Ula's Temple is kinda slowly becoming a thing now.) Though I like card:Aquitect's Will a HELL of a lot better for islandwalking purposes, Spreading Seas is decent if you see a lot of Tron or Affinity. (Turning a Blinkmoth Nexus or Inkmoth Nexus into a island is really a pain in the ass.)

JayZ1483 if you don't see a lot of tron or affinity the card:Aquitect's Will will suit you better. On the other hand, you could always do a 2/2 split and cover both bases.

That's true, running 2 of each is probably the best way to go

I like that you run card:Aquitect's Will

You may also want to test Cold-Eyed Selkie in place of Sygg, River Cutthroat to find which is better for you.

I personally like Cold-Eyed Selkie because it can draw you more cards. You may like Sygg, River Cutthroat because you can play him, swing with other fish and draw a card, but you can always use AEther Vial to get Cold-Eyed Selkie into play at the end of your opponent's turn so it can swing (assuming you have used Spreading Seas , card:Aquitect's Will or they just have an island, it will be unblockable, and it is pumped by your Merrow Reejerey , Master of the Pearl Trident , Lord of Atlantis and lv 4 Coralhelm Commander ). Also, Cold-Eyed Selkie isn't legendary like Sygg, River Cutthroat is, but it does cost 1 more mana.

Hmm....I'll have to playtest with both to see which I like better, but Cold-Eyed Selkie sounds like it would be a good addition

I used to run Cold-Eyed Selkie and found he never pulled his weight. I'm getting much more cards drawn with Sygg, River Cutthroat in my testing.