least sensitive

Need a little more info such as tank size, etc. There are lots of fish that are hardy but they can't all go in the same sized tank. Some of the hardier fish are Clowns, Damsels, some Gobies, Blennies, certain sp of Wrasses (especially the Thalassoma sp), and Triggers are probably the hardiest. Anyway hope this helps and good luck!

There is no doubt that damsels are the toughest little guys available. When I bought my first saltwater aquarium, I did not know how much salt was required to reach the correct gravity of ocean water. I bought a small box of instant ocean -- thinking it would be enough -- and it only raised my tank's salinity to 1.005. The pet store was already closed by the time I mixed it, so I could not just go get more.

It seemed certain that the damsels were doomed, but they survived the night! I went to the pet store that morning and bought the biggest bag of salt I could find. The water was raised to its proper salinity, and the fish continued to live with no problems;I actually had to get rid of them before I could put non-aggressive fish in the tank.

yeah, damsels (clowns included, they are damselfish, you know) are the hardiest SW fish out there, especially if they are tank raised/bred.