If you want to become a fisherman in Bitlife, you will need to search for the job under careers. However, be warned as the job can be pretty tricky to find and rarely shows up under the list.
It also has low entry requirements on the plus side, meaning you don't need to have a fancy college degree; you just need to have an adult character. On the downside, the job pays very low, so it's not the most ideal job to have.
Nonetheless, you can find the job when it shows up under the job list as fisherman, and you will need to apply to it to become a fisherman. Once you apply and get accepted, you will become a fisherman, that is if you can find the job first.
If this isn't the case for you, you can always try restarting your Bitlife app or aging up, as both can sometimes refresh the job list. You can also try moving to a city that is close to the water in real life - this may not work, but worth a shot.
Eventually, the job should show if you try one or all of these things, and when it does, just follow the steps laid out in this guide to become a fisherman in Bitlife.
For more on Bitlife, check out How to get a Boating License in Bitlife and How to become a Pilot in BitLife – Pilot License Test Answers!