Red Spotted Goby, Trimma rubromaculatus

2 introduced on the 25th June 2017. The smaller one vanished after just a month (28th July 2017). Rocket, the remaining goby, vanished on the 29th December 2018 after a year and a half in the tank. Was it old age or some other reason? I had noticed that he wasn't eating as well in the few days prior to his going missing.