My Pearl Goby just died ☹

Here is a picture of him:

I think he died due to malnutrition. When I bought him he was very thin - almost like here. But it was my fault that he died. See I had him since 10 September and thus I could have kept him longer in QT until he was nice and fat again. But instead I thought he would have more food in the main tank thus get better faster. I guess I was wrong ☹