Crabs with black gills recently turned up in Mississippi (wlox story). Local fishermen say they have never seen anything like it, but are worried these crabs are stained with oil. Black gills in crabs can be associated with disease ("black gill syndrome"), low oxygen levels, high levels of detritus, and pollution or a combination of the above.
Testing has so far indicated that oil is not involved, but that low oxygen levels and detritus are more likely causes (oilspillaction.com).
“The FDA has advised that, following extensive sensory testing and chemical
analysis, tissue samples tested indicate that crabs from these previously closed
areas south of the barrier islands are safe for consumption,” stated a news
release from DMR and DEQ. “Testing for crab tissues includes specimens of
special interest, such as those with dark gills, brought to DMR’s attention by
concerned fishermen and the public; all of these samples have been determined to
be safe for consumption as well.”
Jewell said no exact cause has been determined for the dark gills found
on some crabs, but low dissolved oxygen levels and sediment are suspected.
“A lot of the low dissolved oxygen in our waters is because we have
very high temperatures,” he said. “That can be part of the issue, but I don’t
think it is any one thing.”
The crabs with dark gills that been brought to DMR by the public have
come from upper bay areas, he said. “There is a lot of sediment and a lot of
suspended sediment and that tends to get entrapped on the crabs’ gills,
particularly crabs that are stressed.”
The darkening is not found on any other crab organs, he said, “which
tends to indicate it has to do with respiration.”
Crab samples tested, including the dark gills, have returned as free of
oil or trace amounts in the parts per trillion range were found, he said.
“Anything they are finding is way below the NOAA protocol,” he