Veterinarian here. Small animal, not fish specific. People keep talking about cyanide, and I'm with Jay on that one, dont think it's the case here. I do however wonder if it's an environmental toxin (runoff) sensitivity or people using chemicals other than cyanide to trap fish. Organophosphates would come to mind for me. They would stun fish as they are a neurotoxin. The fish could potentially recover. And guess the long term effect? Neurologic disorder, more specifically demyelination of nerve sheaths. Which nerves have the thickest in animals? Peripheral nerves. And organophasphates are still pretty common pesticides around the globe. Maybe wrasses are more susceptible to effects? Maybe it's incidental.
Another thought would be a parasite. There are plently in the animal kingdom that cause neurologic disease, and several are protozoas that we know are difficult to kill. It's gonna be tough and expensive to figure it out. We have a fish vet enthusiasts forum on Facebook, and I know a few people have sent fish in for pathology to Idexx, so that may another source. I think it's around 200 to 250 for pathology through them.
I don't think this is from run-off. Many of these wrasses are deep water fish, found far from any inshore areas. If it was an environmental toxin, I would suspect other species would show with problems.
Personally, I think it is a virus. We already have the case of the Banggai cardinalfish - previously a very hardy species until they began getting collected and held in close quarters. Now, they are as weak as kittens and have a horrendous mortality rate. Here is a write-up I did on that issue:
Banggai Cardinalfish Iridovirus (BCIR)
This fish was originally discovered in 1933 but then lost to science for about 60 years, when the Banggai cardinalfish (Pterapogon kauderni) was “rediscovered” and began entering the tropical fish trade. Aquarists noted how hardy the species was and that they were very easy to reproduce in captivity. A decade later, the price for wild-caught Banggai cardinalfish had decreased fivefold, but the animals were now considered very delicate, with high losses seen in newly acquired wild fish.
What was the cause of this sudden change in the apparent health of this species in captivity? Poor handling, collection with cyanide (unlikely), and bacterial disease were all suggested as possible reasons for this change. A researcher then published a study showing that the presence of an iridovirus was associated with episodes of mass mortality in newly imported cardinalfish (Weber et al. 2009). A similar virus has since been isolated from the common batfish, Platax orbicularis (Sriwanayos et al. 2013), but a corresponding high mortality in aquarium fish of that species has not been noted, perhaps because many fewer batfish are imported for the pet trade than the ever-popular Banggai cardinalfish.
Since there is no cure for this viral disease, captive-raised fish that were never exposed to wild stock, or fish that have subsequently developed immunity by surviving an infection would be the best choices for aquarists. Avoid inexpensive wild-caught Banggai Cardinalfish. Not only do they have a poor survival record, but they’re also being collected at such a high rate that wild populations are locally threatened with extinction.
Jay
