I've seen quite a few fish I suspected were poisoned over the years but short of doing tissue sampling there is no way of proving it. It has been said that up to 75% of cyanide poisoned fish die immediately and the rest generally have enough damage done to them that their lifespans are greatly shortened at best. From what I gather cyanide affects the bloods ability to carry oxygen by binding to the hemoglobin and organ failure from a lack of oxygen is what causes the actual death. There have been cases of cyanide poisoning in humans that eat a steady diet of cyanide caught fish, these people are unwittingly killing themselves in some cases.
Certain fish species are more prone to cyanide collection, those swift, wary and smart reef fish like tangs, angels, triggers, and groupers. Those fish that see a diver coming and seek refuge in the reef are those most likely to be collected with poison. If I were in the market for an angel I would definately avoid the "Indo-Pacific" label and would want to know exactly where my fish was coming from. I think most of the big online fish supply shops are pretty up front about where the fish are coming from, they have too much to lose to try and pass off sick fish. Another way to be sure to get a fish from a good collection area is to buy a fish like a Red sea regal angel or a personifer angel that only comes from these areas. Be prepared to pay a lot more for a fish that comes from a location/collector that properly hand catches its fishes.
I read that nearly 2/3 of all fish hobbiests polled said they would pay up to double the price if they could be guaranteed a healthy hand caught fish. By nearly the same margin the same respondents also said they didn't trust the fish industry to enforce any such system.
