Not to go too far off the trail here, but I often say that I think the fish in this hobby are
a lot more challenging than the coral.
To wit, I can tell you with exacting detail in chemical, electrical and hydrological terms how to set up a system that (if done correctly and consistently) will keep 99% of corals happy and growing. The corals will never jump out of the tank, never quit eating for no reason, etc.
I can tell you a "few things" that "most fish" like....but that advice is mostly not universal, even just among the small number of species in a typical LFS. Even the best salinity for them is still widely debated on forums! When you get down to the individual fish level, they're about as unique as people - down to the fact that some will just refuse to eat in their new "prison" even if it means they starve to death. Unlike corals, there are no tests I can run to see how I'm doing with my fish...can't check their calcium levels, right? LOL. That's a lot to deal with as a keeper!! ;-)
All of this is the reason I actually focus a lot more on coral. (No offense to my three awesome Barnacle Blennies in their 50 gallon castle! LOL. (
movie) Perfect size fish for the typical home reef.) To me, most coral are much more adaptable to our little wet boxes than most fish - therefore fish (especially when plucked from the wild) should get a little more consideration than I think they often do.
-Matt
P.S. Here's a link to
ORA's Blennies, similar to the type I recommended. A Blackline or Smiths would probably be my choice, but they're all pretty neat looking. You may have to see them in person and how they act to appreciate them. Farmed species like these would be one possible awesome substitute for a Cleaner Wrasse.
P.P.S. Did we all fall down for not mentioning the most obvious substitute -
ORA's Neon, Sharknose and Yellowline gobies? (I did....sorry.

) The Neon is a (smaller) dead-ringer for the Cleaner Wrasse, and
all of these three gobies are known to clean pretty much like the wrasse. They are known to get along well with clams and just about everything else in existence.

And again they're farm-raised. Much less skittish than the wrasses too...ultimately a more enjoyable fish to watch, IMO.