Fish Lesions Likely Result of Freshwater Influx
By DAVID RAINER
When dead or obviously distressed fish started showing up on the Eastern Shore this spring, anglers and residents were noticeably alarmed.
However, after exhaustive investigation by the Alabama Department of Conservation and Natural Resources’ Marine Resources Division and Auburn University there apparently is no widespread viral infection and the likely cause of the dead fish and fish with rashes and lesions is a culmination of environmental conditions.
Auburn was able to isolate two infections for some of the affected fish, which were stressed by unusual weather conditions, according to Vernon Minton, Director of Marine Resources.
“There was a Mycobacterium that was on the skin and nothing in the internal organs,” Minton said. “And there was a fungus, Aphanomyces invadens. That pretty much has a world-wide occurrence, typically triggered by environmental changes – a lot of freshwater, temperature changes and so forth. It will kill fish. If you go to the Web and look it up, it’s a perfect match with the lesions.
“The rashes, we haven’t gotten anything back on that yet. We’re sending some of those samples to Robin Overstreet at the Gulf Coast Research Laboratory in Ocean Springs (Miss.). Dr. Overstreet has been in this business a long time.”
Minton said a 100-percent positive diagnosis of what caused the incident is not possible.
“The reason it’s so hard to ID these critters is we have to find specimens that have the lesions that are still very much alive,” he said. “If you sample dead fish, then the other types of bacteria that normally break things down are already there. So actually picking out the causative agent is difficult. You end up with an alphabet soup.
“Most of the specimens we’ve sent off were in pretty good shape, but there were a few where they couldn’t identify anything other than the normal fauna you see in the water all the time.”
The dead fish brought back memories of 1995 for long-time Gulf Coast residents when hardhead catfish began washing ashore by the thousands.
“I guess what’s strange this year is the number of species that has been involved,” Minton said. “Normally we see mullet every year with lesions because they get up in fresh water and the temperature drops or something like that. Their immune system is not as strong as it normally is, and sometimes they just pick these bugs up. It’s like any critter, if their resistance is down for one reason or another, it’s easy to pick up an infection.
“But this year we’ve seen flounder, croaker, spots, red drum, spotted seatrout, sheepshead, catfish – a whole variety of things. We haven’t seen large numbers, compared to what we saw in ’95 with the catfish. This (current) thing started with hardhead catfish and then shifted to other species. Back in ’95 hundreds of thousands of catfish were killed basically along the entire Gulf Coast. Texas got hit really hard. They did think it was a virus at the time, but it looked an awful lot like this fungus, too.”
The Alabama Gulf Coast saw two periods of heavy rain where more than 7.5 inches fell in a three-day period in late March and almost 3 inches fell in one day in April. Flash flooding with significant runoff occurred during both downpours.
“This seems to have occurred from Weeks Bay north up the Eastern Shore,” Minton said. “And that makes sense in terms of fresh water coming down. We had a couple of real heavy rains this spring that really freshened Mobile Bay. We had a spoonbill catfish (paddlefish) show up at Dauphin Island. That thing shouldn’t be down there. We had dropping temperatures and it was windy. All of that put together will stress fish.
“Auburn, in its summary, felt like it was an environmental incident – a change in the water temperature and salinity and so forth.”
Auburn’s summary stated: “Many factors can influence how diseases manifest themselves in each species. Due to the large amount of freshwater influx many environmental parameters can change rapidly, such as temperature, pH, salinity and increase in runoff pollutants. Each species has a different threshold of tolerance for any of these, and each will react differently in response to these sudden changes. …This supports the theory that it was a rapid change in environment that increased the stress levels on the fish and lowered their ability to resist infection/disease.”
Of the six fish sampled so far (more fish are currently being tested) three showed evidence of Aphanomyces invadens infection, while one was found with a Mycobacterium marinum infection. One fish was caught in a trawl and was deemed not suitable for diagnosis, while one fish was considered injured during the angling process. The report also indicated that one fish with a lesion with Aphanomyces was in the process of healing and would have likely healed completely.
“After we open shrimp season, you’ll see fish banged up from encounters with nets and they’ll get a secondary bacterial infection,” Minton said. “A lot of them won’t make it, but some will recover. Sometimes you’ll see fish like redfish with indentations where they’ve recovered from that or you’ll see spear marks where something like a great blue heron has hit at them. They were just lucky enough to get away.
“Everything has a life limitation and we do get some hooking mortality, even with red drum, as tough as they are. I do know that a lot of people are targeting the bull reds, especially when red snapper season is not open.”
As stated when the incident was reported, Minton maintains his position that any fish with lesions or that appears distressed should not be eaten.
“I think it’s a good idea to not eat anything that shows signs of sickness,” he said. “We talked to the State Health Department folks, and they agree that if a fish has lesions it’s just not a good idea to consume it. It might not ever bother you, but I would personally recommend you not consume it. And I would suggest you wash up after contact with an affected fish. There are certain types of infections, like the pfiesteria on the East Coast that people can catch. Fortunately, we haven’t seen it down here.”
Gulf Coast water also hosts another bacterium, Vibrio vulnificus, that can be very harmful if an individual becomes infected and is not treated promptly. Fortunately, Vibrio usually only affects people with an immune deficiency.
“It’s highly recommended that if your immune system is compromised that you not consume raw seafood,” Minton said. “We have between 12 and 14 deaths per year from consumption of raw oysters. That’s nationwide. We’ve never had a death caused by Alabama oysters. In every case, 100 percent of the time it’s someone with an immune problem.
“Vibrio is a normal inhabitant of the water, but it usually doesn’t get into concentrations enough to cause a problem. If you get something like that – like a crab scratches you and you get poked by a shrimp – the red streaks that indicate an infection, you should see a doctor immediately. It can be very serious. Most of the hospitals and doctors in this area are aware of it, but if someone is just visiting and goes back home to Birmingham or Decatur, those health professionals may not know what they’re looking for. It is treatable, but it is hard to cure if it isn’t treated in a timely manner.”
The good news is the reports of fish with lesions or other maladies have been on the decline. One guide I know who fishes the Fort Morgan area said he has caught over a thousand fish without a single lesion, while another guide from that area has only seen a couple.
“It seems to have died down quite a bit,” Minton said. “I talked to commercial fishermen recently and they have seen a few fish with lesions but not any big numbers. I think it’s just a matter of everything leveling out. Typically, saltwater fish can go up in salinity without a problem. But when the salinity goes down, especially if it happens very quickly, then they get stressed.”
PHOTOS: An Atlantic croaker (top photo) and a southern flounder display lesions that were caused by the Aphanomyces invadens, a fungus that will attack fish that have been stressed by a freshwater influx similar to what occurred in Mobile Bay this spring.