before I started my career in wastewater, I was an assistant manager at a very large fish store (180 tanks, 4000 gallon shark tank etc) for a fewl years.
I have 8 tanks currently:
90 gallon freshwater with large barbs, silver dollars etc.
65 gallon saltwater (with formerly brackish Monos and archerfish)
65 gallon fresh (more large fish)
3 30 gallon planted tanks
10 and 20 gallon planted guppy tanks.
Your coris wrasse is likely still hiding in the gravel. Try feeding some frozen brine shrimp or even marine flake. Usually, it will take more than a week for him to starve so don't panic yet.
Is the tank an established tank? or is it a new set up?
If it is new, check your ammonia levels in the tank especially if you have added live rock. Uncured live rock tends to spike the ammonia levels in a new tank as organisms that died in transit on the rock decay.
check your specific gravity also (usually at least 1.017 to 1.020 is generally good).
are their other fish in the tank? hopefully nothing too big as yellow coris wrasses do not get very big.
first thing to do is check your water chemistry - you should make sure you have basic test kits on hand (ph, nitrite, nitrate, ammonia, hydrometer etc)
saltwater fish are too costly to take chances on! check your water at least weekly.
