Aliens are your number one enemies in Insaneaquarium.
Sylvester. basic alien.
Balrog. same as sylvester, just a little stronger.
Gus. dies by eating fish food and guppies. Signature is type-G
Destructor. stays on the ground, fires missiles.
Ulysses. Like destuctor, but shoots stronger projectiles.
Phycosquid. sometimes goes dormant. while dormant, he will not attack and if you attack him, he will gain health
Bilaterus. Has two heads.
Minisilvester. spawned by cyrax. sightly weaker than silvester.
Cyrax. Sumons Minisilvesters and other aliens. kill him to win the game.