What can I do at the Fishmonger's?

You can actually have some fish here. Not eat it, though.

You can weigh it.

There are three scales for your convenience.

And six pre-weighed fish on ice.

It almost looks like a puzzle.

Is that a date on the BLACKBOARD near the exit?

Or maybe just a series of three numbers?

Try and place the fish on the scales so each scale shows 5, 7 and 12 respectively.

(SOLUTION FOLLOWS)

↓

Place the fish labeled 2 and 3 on the first scale, the fish labeled 6 and 1 on the second scale, and fish 4 and 8 on the third scale.

Now go and see what happened down in the cellar.

Some peculiar LOCKS were revealed.

One is even shaped like a fish.

Take a closer look around the shop.

Have you found the KEY yet?

It's hiding among other fish.

Look closely on the fish poster behind the scales.

The second fish is actually a key.

Use it on the fish-shaped lock in the cellar.