As their name implies, Spreaders cover large areas with purple ink, erasing your ink in the process. Instead of firing ink across these areas and trying to race ahead, avoid the Spreaders. Simply ride atop the Spreaders while crossing these areas. You can even ink the top of the Spreaders, and hide in your ink. But there’s an Octotrooper already riding the third Spreader in this area—splat him and then step onto the Spreader to cross.
Watch out for the Octodiver hiding in the purple ink at the base of this wall. These enemies remain submerged in their ink until you approach, attempting to ambush you. Either target the Octodiver directly or hit the Balloon Fish on the Spreader above to rain down your ink. Afterward, make sure the Spreader is coated in your ink, then swim up the Spreader (or wall) to reach the next launchpad.
There are four Octotroopers (including one Shielded Octotrooper) guarding these Spreaders in front of the Zapfish. Stay behind cover to avoid being detected, then step out to shoot the Balloon Fish in the center. The resulting explosion of your ink is powerful enough to take out a couple of the enemies, including the troublesome Shielded Octotrooper. Stay behind cover and throw Splat Bombs at the remaining enemies, tossing the bombs just ahead of the Spreader the enemies are riding on. This clears the path to the Zapfish.