When I first got the goby I had no clue. They told me he was freshwater, ate other fishes and was aggressive. Took me 2 days to noticed he wasn't happy. Did some research and got my eyes opened. Went and got him his own tank, added some mollies, a pair of sharks, and some chromides to help keep the mollies in check. Boy did he get fat and happy! At night under the blue lights I will see him swimming all over the tank. Floating on the bubbles and just enjoying himself.