That recipe is for guitar fish, not guitar. I have no guitarfish in my freezer. I have some shark meat. I suppose it could be substituted. The only problem is that I have pounds of shark meat, not grams. I've caught many sharks over the years, but I've never caught a metric shark. I don't think they inhabit this part of The Gulf of Mexico. The nearest place where they use the metric system is Mexico. I suppose a few metric sharks, (and maybe metric guitarfish as well) show up in the waters near the US/Mexico border, but that's 700 miles from here. Not gonna drive that far.