This fish is regularly sold here in Brazil as a freshwater fish, but is a huge mustake, it is in fact a brackish one and needs a large amount of salt in water and high pH to live well and even eat. Many times, they're maintained in pH 7,2 or even lesser and without salt and they starve till die. In fact, they go very well with Scat for ex. (they have the same salt necessity, for instance) or other gobies. I never heard about a violet goby eat some fish, only bloodworms, artemia, fine meat and small pellets. In nature, they live better with sand, what they filter putting it in their mouth.