The main groups of fishes are lobsters, swordfish, monkfish and sharks. Lobsters and swordfish are the only profitable fishes to be caught in the worlds of non-members. The best fishing spots are close to banks, where are located in Caterby and fishing Guild. As a member, when you complete the quest of the Swan Song, you can fish for monkfish. Musa Point (Karamja) is the only one place for catching lobsters and swordfish. In the worlds of non-members and members, you can exchange your fishes for bank note by talking to Stiles who lives in the south of the volcano.
Become a dog walker if you live in an area where they are in demand. You can walk dogs for people who own dogs but who are too busy to walk them. However, this can be a demanding job, especially if you end up walking a few dogs at once or if you are walking dogs throughout the day, so ensure that you have the physical stamina for this type of job.