Maybe a bit of activated charcoal, citrus or eucalyptus EO or FO, salt bar, or something scrubby in the actual bar, like ground walnut shells etc.
Those are just ideas.
I have a large fish tank and often when cleaning have my arms up to sholders in fishy smelling water. My arms smell really funky afterwards and it's hard to get rid off the smell only after one shower. I can imagine how it is while working with fish all the time.
I work with fish. If I wanted to make a super duper anti fish yack bar, I would: make it a salt bar (because all the cleansing coconut oil), definitely with Anise EO, maybe some lemongrass, mint or 10X orange EO too, probably some coffee grounds or pumice for extra scrubbiness and perhaps some AC powder as well.
It smells just like a pitzel if you have ever had one of them. Sort of like black licorice. My girlfriend really likes the smell and it is her favorite. I don't mind the smell but really the soap has one job to do and that's remove terrible fish smells which I hope it does.