Gone fishing

I am currently looking after my parents' summer house and today I've had a good friend from law school and her family visiting. Weather doesn't feel like summer, but who cares, at least it is not raining!  We went fishing on the pier, and guess what, we even got some fish. This was my first catch:

But it didn't look any good, so it turned into a catch and release. No idea what kind of fish it was...

Then we got quite a few mackerels. And even an old sock! The sock also turned into catch and release!

I lost one ok sized mackerel while trying to kill it, and then threw a small one back in so that it can grow and get caught next time. But in total, we caught enough for a decent dinner!

One of the small one got the post mortem stiffness quite quickly, so that one almost turned into a flying fish...

Any good suggestions on how to prepare the mackerels? I want to put them on the grill (of course!).