Young grey mullets can be tricky to identify. Here’s a young golden grey (Liza aurata):
… and a young thin-lipped grey (Liza ramada) about the same size for comparison (top). The golden grey is slightly thinner-bodied, and has the prominent golden spot on the operculum. The comparative length of the pectoral fins, which is quite distinctive in adults, is not particularly reliable in young fish or damaged specimens.
To confuse matters further, the thick-lipped grey can also have a golden spot on its operculum.