Susinok, you can also check for diving jobs at the restaurants, the science building and city hall (there may be more, but that's all I've found). The simolians earned from that also up your diving career earnings. Some of them pay well, like delivering 3 eels to the bistro pays about 10k simolians. I did find that if I had more than one family member catching fish from diving, and they gave their catches to the sim with the dive job, that counted towards fulfilling the job.
I also placed a consignment store and my diver sold fish caught from diving there, and that also went towards his diver career earnings.
[Edit - the dive jobs don't seem to help your career, sorry bout that.]