Some sites will tell you that violet gobies aka dragon gobies will eat small fish but IMO this is rubbish. They have huge mouths with what look like teeth protruding from the front of the jaw but are actually filter feeders which feed by taking in gulps of water and filtering the water through the gill rakers to sieve out tiny particals of food. We have one in a 55 community with small fish and have never had one eaten, the goby struggles with large bloodworms let alone being able to swallow fish. This is where the tricky biy comes in, since they are filter feeders they are difficult to feed and need special care to keep alive. They will not take pellet or flake foods and will need to be fed small live or frozen foods every day, daphia, brineshrimp, black mosquito larvae, glassworm and bloodworms will all be eaten.