Do you know what it was being fed before? If not try a mix of things to see what it likes. I usually try my staple food first but remember sometimes a new fish takes a couple days to settle in before it will eat. Usually most all fish I've found will eat frozen brine shrimp which can be a good way to get them eating. Frozen bloodworms usually go over really well too. I've also found New Life Spectrum Thera A is eaten by most all fish. I never had an issue with my Gudgeon eating.
Nice, looks just like mine actually. Do either of yours have black on the outside of their fins? That one looks like a male. I have a young male/female pair so I'm hoping for babies eventually. They are both just maturing and the female has the black starting to show up on her fins. They've been doing a lot of dancing with each other lately which is awesome to watch.
Frozen foods usually work and slowly he should begin to eat other foods you offer.
The pic's are kind of funny as you look like you got him coming and going.