Fish ladders are minimally effective. They are typically installed to add a rubber stamp to dams and say "look, we tried! It's not our fault the ecosystem is getting destroyed". Same thing with fish breeding and release programs.
No doubt there are some ineffective fish ladders out there, and no doubt dams have a negative impact on fish populations. Could better designed fish ladders and compensation channels mitigate the effect of the dam? I think so.
Fish stocks across all species are collapsing due to overfishing.