I even hate to disagree with you, but I must...
Firstly, that item he's holding looks
nothing like the fish food container in the ebay item.
Secondly, Vito picked the item off his desk, AFTER he fed the fish.
Thirdly, that scene didn't occur in 1945 (which is when GF1
started)... it's most likely about 10 years later, shortly before Vito died (1955) when Michael became Don -- most likely 1954-1955 (if my
Timeline is worth anything), just when the transistor radio came out.
I still believe it's a transistor radio.