If you want to eat a cuda, try one that is not caught from a reef (grassflats, inshore channels, etc.)
Then basically you can't eat any from what you are saying. The cudas in deep water also have the poison.
5 lbs. is what I have heard from cudas, other fish maybe larger. The only other species I have heard mentioned to carry ciguatoxin are amberjacks and cubera snapper. I am sure very large snapper and grouper have some small chance at having it, but there aren't very many of those around anymore.
Sorry, but there are members on this forum that has been poison from eating a cuda that less than 5lbs. Larger Snapper and Grouper are acceptable to this poison too.
I don't understand the idea(s) you are trying to convey here.
Let me clarify. I was speculating that, in theory, a fish not associated with the dinoflagellate would have a little to no chance at carrying ciguatoxin. So a fish from an area where this dinoflagellate does not exist, would not be toxic.
OP. You have a higher risk eating fish in the keys. From what I have read, affected areas occur in hotspots. These hotspots are not always in the same areas and a hotspot one day may not be one later on. Hotspots are contingent upon a number of factors that increase the dinoflagellate population. Eating reef fish in your area would require you to decide what an acceptable risk percentage you are willing to take. Some fish of certain size would increase that risk and others would decrease it.
A peer reviewed article I read stated that the general rule is you have a much less chance at getting the toxin by consuming reef fish less than 3-6 lbs. It was also advised that eating smaller portions is a good idea, "It has also been proposed that eating small portions (i.e. <50 grams or < 0.11 pounds) of different fish is safer than eating larger portions of any individual fish that might be associated with CFP."
I found an at home test kit for ciguatoxin. Google Cigua-check to find out the details.