Consider the size. The larger the reef fish, the more likely it is to be ciguatoxic. That makes sense since the toxin concentrates, like mercury, as it moves up the food chain. I've heard various rules of thumb — e.g., any fish less than 5 pounds is safe and some no more than 2 pounds. There is no hard-and-fast rule, but it's empirically evident that larger fish generally account for outbreaks. (The owner of one of the St. Louis restaurants serving meals unaware from a ciguatoxic 60-pound AJ told a newspaper reporter he now understood big fish could be problematic, so he wouldn't serve any amberjack exceeding 25 pounds in the future. In fact, that arbitrary cutoff probably means little.) As an angler, you have the opportunity to throw back larger predators if you wish (unlike diners, who have no way of knowing how large a fish provided the fillets on their plate).