These are all the itmes you can get while fishing in the Underwater Fishing Cave. Hover over the items and a name will appear in a box next to your cursor. These are ordered by level attainable, but these levels are NOT set in stone - they may vary, but most of the time they do not.
Level 1+
Level 5+
Level 20+
Level 30+
Level 40+
Level 50+
Level 60+
Level 70+
Level 80+
Level 87+
Level 90+
Level 100+
Level 110+
Level 120+
Level 139+
Level 167+
Level 179+
Level 189+
Level 222+
Level 244+
Level 250
Level 258+
You can take this 'Bag of Broken Neopoints' to Donny's Toy Repair Shop and for a fee it will be fixed. After being fixed the bag will turn into more neopoints for you to keep! This bag can be caught at level 1 and after.
Once your pet reaches Fishing Level 80 or above, you can catch a 'Titanic Giant Squid'. If you do, you will recieve this avatar.