Did I ever have a fish that refused food??? I wish I had ten cents for every fish that never began to eat after I bought it during my 41 years of marine fishkeeping. Fish will refuse food for a variety of reasons, some minor (stress of a new environment) to truly deadly ( parasite infections), and dozens of reasons in between. Since we are talking about new fish in your case, it could be combination of things. The tank environment is new, so the fish are probably scared. They may not recognize the food as food, so they don't know they are supposed to eat it. They may be ill with a parasite. New fish should be placed in a small quarantine tank and provided with familiar foods (I generally start with something like "Marine Cuisine" which has a mix of organisms in it, or even diced cocktail shrimp or clam (freeze it first to kill any possible hitchhikers). Most fish (except, for example, mandarins that eat only copepods, or tangs that need greens) will eventually take one of those foods, or brine shrimp (nutritionally zero, but can be used to train fish to eat). I then carefully observe the new fish for any signs of disease (scratching, rapid breathing, etc.) for several weeks. If I am suspicious about the source of the newcomer I will prophylacticly treat with a parasiticide or copper (know the particular species of fish, some don't do well in one treatment or another). After the fish is feeding, fat, and recognizes me as the source of all good things it is time for the animal to meet the display tank. You just have to accept that some fish will never adapt, will not eat, and eventually die. All we can do is try to provide conditions and food that the fish finds acceptable, and hope.
