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By Kathy Hart 



Recently, N.C. Sea Grant research- 

 ers discovered a fish killer — a micro- 

 scopic animal that paralyzes fish with 

 toxins and sucks away their flesh. 



JoAnn Burkholder, an aquatic bota- 

 nist at N.C. State University, says people 

 shake their heads in disbelief as she de- 

 scribes the dinoflagellate that appropri- 

 ately is named Pfiesteria pisci- 

 mortuis. It species name means 

 fish killer. 



Sea Grant fish pathologists Ed 

 Noga and Steve Smith of the 

 NCSU College of Veterinary 

 Medicine discovered the di- 

 noflagellate when about 300 fish in 

 a brackish-water aquarium in their 

 lab went belly-up with no apparent 

 cause. The water had been taken 

 from the Pamlico River, but Noga 

 could find no pathogens or bacte- 

 ria. He did, however, find the wa- 

 ter swarming with microscopic 

 dinoflagellates — single-celled 

 animal-like organisms. 



Dinoflagellates aren't unusual. 

 Along with diatoms and other 

 forms of microalgae, they compose the 

 bottom of the aquatic food chain and are 

 among the most primitive forms of life 

 on Earth. But some dinoflagellate spe- 

 cies, such as the red tides, are toxic. 



Noga realized this dinoflagellate 

 was different, however. This dinoflagel- 

 late attacked fish. Its toxicity wasn't a 

 defense mechanism designed to keep 

 fish from consuming it. On the contrary, 

 this dinoflagellate was a predator in 

 search of prey. 



To determine its identity, Noga sent 



samples of the dinoflagellate-infested wa- 

 ter to aquatic botanists along the East 

 Coast. Among them was Burkholder, an 

 NCSU colleague. At first, she was unbe- 

 lieving of Noga's description. But as she 

 and her students began to study the di- 

 noflagellate, she made some startling dis- 

 coveries about this horrific killer. 



Light brown in color, this microscopic 



Pfiesteria piscimortuis 



dinoflagellate is so small that millions 

 would fit on the head of a pin. It's an ani- 

 mal, Burkholder says. But sometimes it 

 masquerades as a plant after eating algae, 

 one of its food sources. 



The dinoflagellate digests all of the 

 alga except the chloroplast, which is the 

 part that draws energy from the sun via a 

 process called photosynthesis. The chloro- 

 plast continues to photosynthesize inside 

 the dinoflagellate cell, falsely giving the 

 impression that the dinoflagellate itself is 

 performing this plant-related process. 



Unlike its close relatives, the red 

 tide dinoflagellates, P. piscimortuis 

 gives no evidence of its presence. 

 There is no discoloration of the water 

 or other obvious clue that it is lurking 

 in the water column or hiding in the 

 sediments. 



It's even hard for scientists such as 

 Burkholder to detect because it trans- 

 forms into at least 15 life stages. It 

 ranges from a dormant cyst in the 

 sediment to a toxin-emitting single 

 cell with threadlike extensions 

 called flagella. 



The dinoflagellate is easiest to 

 detect when it's on the attack, 

 triggered into action by an 

 unknown substance secreted by 

 fish. Then it transforms from one 

 of its resting stages into a swim- 

 ming cell that emits neurotoxins 

 into the water and air. 



The neurotoxins affect the 

 fish's nervous system, causing it 

 to become disoriented and 

 lethargic and to gape for air at the 

 surface. Unless a fish can escape, 

 it will suffocate because its 

 breathing mechanism is paralyzed. 

 Fish can die within minutes of attack. 



As the toxin affects the nervous 

 system, the dinoflagellate attaches itself 

 to the flesh and literally begins to suck 

 the skin away. This releases organic 

 matter into the water that attracts more 

 dinoflagellates and sends the one-celled 

 gametes produced by the parent cells 

 into sexual reproduction. 



Now the water is swarming with 

 hungry dinoflagellates emitting more 



Continued 



COASTWATCH 19 



