Coudal Partners: Whose Fish?

I rather doubt the claim that this logic puzzle was written by Einstein, but it is tricky. Hint 4 is vague—does “on the left of” mean the precise “left neighbour of” or the looser, and tougher, “somewhere to the left of”? I suspect the former; there are multiple consistent solutions to the version with the looser constraint. (via Signal vs. Noise)