Green’s Dictionary of Slang

on the lookout (for an advantageous opportunity).

1962		R. Cook Crust on its Uppers 19: I assure you I’m all about trout.
2021		J. Meades in Critic June 6/2: They were part of a tribe [...] who were, in the words of [Ann] Bar’s sometime boyfriend Robin Cook (aka Derek Raymond) ‘all about trout’, i.e. on the qui vive.