You have a MainActivity which uses the activity_main.xml file and adds a click listener to the button:
This brings you to PageThree, which uses fishguide.xml, and adds a click listener to the button:
This brings you to PageFish which uses fish.xml, and doesn't do anything:
You need to make that third activity add a click listener to a button to direct to the fourth page.
You also have a handful of other Activities (MainActivity2, and MainActivity3, and PageFishLast) which use the same layouts but aren't actually displayed,
you should get rid of them since they serve only to confuse.