There is no fish per inch rule that is relevant in saltwater. In a 80g tank you could have 3 fish or 10 fish, all depends on their size, tempermeant, swim space and how much they contribute to the bio load ie: pooping etc.
What type of fish did you have in mind?
180g Reef - 60g Rimless Reef -90G FOWLR- 125g Malawi Cichlids- 40b REEF- 34g Fresh Planted-working on- 20L FOWLR- working on
I have a mix of many different saltwater fish amongst my tanks, but I love my Tangs most of all.