Not to make too much of a deal about this, and I'm somewhat uninformed about marinating fish, but my understanding of a marinade is to tenderize and imbed a flavor. Fish are rarely tough to the point of needing to be marinaded, and any imbeding of flavor can be done in about 15 minutes, or more simply, make a sauce with the flavor you want. In my mind, and I may be wrong, but a long soak marinade for fish just might ruin it and turn it into mush.