Fish ID - from a fin?

Fish ID - from a fin?

Observation - Fish ID - from a fin? - UK and Ireland. Description: Maybe asking too much to identify a sea fish from its fin only! Several of these fish were swimming around in shallow water (2/3 feet deep) close to shore, at high tide. Not visible in the photo but the shadows in the water suggested they were about 30c

Maybe asking too much to identify a sea fish from its fin only! Several of these fish were swimming around in shallow water (2/3 feet deep) close to shore, at high tide. Not visible in the photo but the shadows in the water suggested they were about 30cm long. I'd guess the height of fin showing is 6-8cm.