Thor had a few projects he was working to keep him preoccupied, but Loki's absence hadn't gone unnoticed; instead of interjecting himself where he might not be wanted as he used to, he waited for Loki to extend the invitation.

And when he did, Thor immediately dropped everything he was doing to see his brother. The fish were just an added bonus.

Thor raps on the door to Loki's room, then opens it (a change from his usual knock-and-wait) and immediately asks: "Where are the fish?"