As you will see, it exists in the standard newcomb, but not in this variant.
To directly address your fish example: If, in the standard newcomb, my mind had been different, seeing the fish wouldn’t necessarily have caused me to make the same choice.
In the modified newcomb, if my mind had been different I would have seen a different thing. The state of my mind had no impact on the outcome of events.
My explanation of what I mean by choice is here: http://lesswrong.com/lw/2mc/the_smoking_lesion_a_problem_for_evidential/2hyu?c=1
As you will see, it exists in the standard newcomb, but not in this variant.
To directly address your fish example: If, in the standard newcomb, my mind had been different, seeing the fish wouldn’t necessarily have caused me to make the same choice.
In the modified newcomb, if my mind had been different I would have seen a different thing. The state of my mind had no impact on the outcome of events.