Disease can spell disaster 



(Continued from p. 1) 



Two years ago a shrimp culture operation in Hon- 

 duras was on the verge of bankruptcy. For six 

 months production had come to a virtual standstill. A 

 persistent problem with fungal disease was rapidly 

 gobbling up profits. 



After local efforts to pinpoint the source of the dis- 

 ease failed, company officials turned to Sea Grant 

 researcher Chuck Bland of East Carolina University 

 for help. With his guidance they were able to clear up 

 the disease and get production rolling again. 



Bland is a mycologist by training. Over the last 

 seven years he has become an authority on the many 

 fungal diseases which affect cultured Crustacea. His 

 work with shrimp, crab and lobster has shed light not 

 only on the biology of these diseases but on possible 

 controls. 



Bland (left) and graduate researcher Laddie Crisp 



According to Bland, pathogenic fungi enter culture 

 operations in basically two ways. They are either in- 

 troduced via the water system or carried in by cap- 

 tured wild stock. Once in the system, the fungi mul- 

 tiply and infect the cultured organisms, breaking 

 down their muscle tissue and eventually killing them. 



Bland believes that filtration and chlorination of 

 the water system are essential steps in reducing the 

 incidence of fungal attack. But, he warns, water 



treatment alone is no guarantee that the fungus will 

 be controlled. "Some sort of treatment of the 

 organism is necessary," Bland emphasizes. 



Currently Bland is testing various chemicals to see 

 how well they work as fungicides on cultured 

 Crustacea. To date his most encouraging work has 

 been with a chemical compound known as malachite 

 green. 



Researchers have known for some time that the 

 chemical is effective in controlling fungal diseases in 

 fish culture. Bland was the first to confirm its effec- 

 tiveness on Crustacea. Although no one is certain how 

 the chemical works, Bland speculates that it 

 somehow interferes with fungal respiration. Today it 

 is successfully being used as a fungal disease control 

 in experimental hatchery situations. 



But because malachite green has been implicated 

 as a possible carcinogen, the Food and Drug Ad- 

 ministration will not authorize its use in commercial 

 operations. As a result, Bland is also looking into 

 other chemical treatments that may have greater 

 potential for FDA approval. 



Of course he hasn't given up on malachite green. 

 "I'm still a little bit hopeful for it," admits Bland. 

 Through cooperative work with the University of 

 Arizona's Environmental Research Lab, he is using 

 radioactively labeled malachite green to trace 

 chemical residues in shrimp tissue 24 and 48 hours 

 after treatment. Results from preliminary tests in- 

 dicate that there is no buildup of the chemical. If 

 further testing confirms these findings, then 

 malachite green may have some potential use in the 

 future for disease control. 



To help aquaculturists concerned about fungal dis- 

 eases, Bland is also preparing a handbook on the 

 diagnosis and treatment of fungal diseases affecting 

 crustacean culture. According to Bland, the 

 handbook has a two-fold purpose. First, it will help 

 aquaculturists recognize the more common dis- 

 eases. Secondly, it will tell them how to prepare and 

 ship specimens to labs for diagnosis and valuable 

 treatment information. 



Although Bland believes disease control is a critical 

 step in eliminating many of the economic uncertain- 

 ties of aquaculture, he is doubtful that the problems 

 of disease will ever completely disappear. Viral, 

 nutritional and bacterial diseases still wreak havoc 

 with many culture operations. Finding treatments 

 for them involves many of the same difficulties as 

 fungal disease control. 



"Two years ago I would say that fungal disease was 

 the most important factor in limiting the develop- 

 ment and success of crustacean aquaculture. Today 

 viral disease is probably the biggest problem. . .1 

 don't think all of the diseases will ever be controlled. 

 Something will always be cropping up," he concludes. 



