From the title: I'm in ur post! shakin mah fish! (hold your mouse over the emote)
That means it's a fish. Strange enough, the fish has the same color of the emote that's holding the fish. It's not impossible that that's the reason this specific emote and this specific fish are combined. For as far as my knowledge goes, shaking fishes doesn't improve their health, more importantly, especially when executed outside the water, it may even bring damage to them. This may bring us to two conclusions: a) The fish and the emote are well acquainted, they are interacting in a way that's most likely normal for them but beyond our level of understanding. b) The fish and the emote are arch enemies. The emote has already killed the fish, and squeezes his eyes because of the smell of the dead fish.
Another but very uncommon theory is that the emote is shaking the fish as a threat.
Since the fish is out of the water and there's no sign of gills, it must be a mammal. It's blue so it must be a baby blue whale.