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Toxic Algae in Shrimp Ponds
A Discussion from the Shrimp List
Craig Browdy (firstname.lastname@example.org): I just read an article by Alonso-Rodriguez and Paez-Osuna entitled Nutrients, Phytoplankton, and Harmful Algal Blooms in Shrimp Ponds (Aquaculture 219-317-336).
We have found some interesting and sometimes scary critters in our shrimp systems over the past year or two, but have never really traced mortality or slow growth back to a specific algal toxin. Most shrimp farmers have likely experienced DO problems associated with a crash of a particularly rich algal bloom, but I was hoping to get some feedback from you shrimpies on specific experiences with algal toxins in shrimp systems.
If this is a common problem why isn’t it more discussed in trade and academic circles? If it is not a problem, why isn’t it, since we have such nutrient-rich systems?
David Griffith (email@example.com): Growers in Ecuador experienced heavy mortalities early this year (December 2006 to January 2007) of shrimp in polyculture with tilapia due to a massive bloom of Chattonella in the Gulf of Guayaquil. As far as I am aware the bloom affected only shrimp in polyculture with tilapia in a rather limited area. Tilapia and shrimp in monoculture were not affected. The mode of action was not identified, but gills of moribund shrimp were found to be heavily infested with the flagellate.
I have also seen (many years ago in Peru) heavy mortalities in larvae caused by chain-forming dinoflagellates with very large cells. The chains, which form a mucilage sheath, are visible to the naked eye, albeit with a good squint, and cause molting problems in zoea, mysis and early postlarval stages.
Gintautas Stasys Zavadzkas (firstname.lastname@example.org): While working for OceanBoy Farms in Florida, we had several low-salinity (2-4 ppt) ponds that showed the typical symptoms of hemolytic enteritis. The lab showed Vibrio—and lots of toxic algae, composed of several different species, none of which were predominant, but the percent of toxic algae was over 60%, creating the enteritis, weakening the shrimp and stimulating an opportunistic attack of Vibrio.
In Texas, zero-exchange systems have had Vibrio problems, but I don’t know if any of them did algae profiles.
Systems that received no natural light experience Vibrio mortalities that were resolved with probiotics, but that’s not so easy to do when you have toxic algae.
Pablo Intriago Legarda (email@example.com): Besides one report of the presence of Gymnodinium catenatum, a PSP dinoflagellate associated with the 2000 La Niña, we have not seen toxic dinoflagellates in Ecuador. On the other hand, reports of toxic red tides in Peru, Chile, both the Atlantic and Pacific coasts of Mexico and the east coast of USA are common. Species such as Trifolium alexandrinium, Protogonyaulax, Dinophysis, and in the states the well-known T. brevis and the very toxic strains of Pfeisteria cause most of the problems. There is not much information on the mode of action of toxins on invertebrates. There are several studies with zooplankton, for instance, on the effect of feeding a toxic strain of Alexandrinum to copepods. Resistant copepods took longer to develop and fecundity dropped. It was also found that male copepods are more susceptible to toxic algae than females.
Blooms of the dinoflagellate Prorocentrum minimum have been shown to be the cause of heavy mortalities of oyster larvae in hatcheries in Virginia and Maryland.
There are a few reports on the effect of some strains of Oscillatoria on Penaeus larvae, as far as I remember, a couple of these studies reported hemolytic enteritis.
Sources: 1. The Shrimp List (a mailing list for shrimp farmers, “firstname.lastname@example.org”). Subject: [shrimp] HABs and shrimp culture. August 14-29, 2007. 2. Bob Rosenberry, Shrimp News International. Update. March 22, 2017.
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