EFFECTS OF UNIALGAL AND BACTERIA-FREE CULTURES OF 



GYMNODINIUM BREVIS ON FISH, AND NOTES ON 



RELATED STUDIES WITH BACTERIA 



By Sammy M. Ray and William B. Wilson, Fishery Research Biologists 



Association of the dinoflagellate Gymnodinium 

 breiis Davis with the mass mortality of marine 

 animals that occurs sporadically in the Gulf of 

 Mexico is well established (Davis 1948; Galtsoff, 

 1948 and 1949; Gunter et al., 1948; Wilson and 

 Ray, 1956; Woodcock 1948; and others). In- 

 direct evidence presented in these papers strongly 

 supports the contention that 0. breiis is the cause 

 of fish kills, commonly referred to as red tides,' 

 when its concentration reaches the order of 

 himdreds of thousands to millions of organisms 

 per liter — concentrations as high as 50 to 60 

 million organisms per liter have been reported. 

 This evidence includes (1) the presence of dead or 

 dying fish in water containing such concentrations 

 of (r. brems, (2) laboratory demonstration that 

 water containing great numbers of G. breiis is 

 toxic to fish, and (3) demonstration that sub- 

 stances toxic to fish may be extracted from water 

 infested with 6. breiis. Further evidence of a 

 more direct nature is provided by the demon- 

 stration that unialgal cultures of 6. brems are toxic 

 to fish (Wilson and Collier, 1955). 



Development of stock unialgal cultures of 

 G. breiis opened the way for the elucidation of this 

 organism's role in the mass mortality of marine 

 animals by making available an abundant supply 

 of material for controlled experiments. Previous 

 to this development investigators were handi- 

 capped, since the suspected causative agent was 



' Tfio term "red tide" is Rpnprally applied to discolored sea water regardless 

 of causes or consequences; tliat is, the causes of the discolorattons may vary 

 from "blooms" of many difTerent microorganisms to nonliving agents such 

 as iron compounds; and the mortality of animals, especially fish, may or may 

 not be associated with such discoloralions. To avoid confusion, we believe 

 it best to refrain from using this popular though nonspecific term In scientific 

 publications. If a popular name is used, we propose that the name "brevUi 

 red tide" be applied to the mass mortality of marine organisms associated 

 with Oymnodinium brevia. 



Note— Approved for publication, February 8, 1957. Fishery Bulletin 123. 



unavailable for study except during outbreaks. 

 Even then, their material was limited to raw 

 samples from the infested waters which contained 

 numerous other organisms. In addition, raw 

 samples were probably held under conditions un- 

 suitable for the survival of G. breiis. 



The next approach to this problem was to 

 obtain bacteria-free or pure cultures of G. breiis. 

 This isolation is necessary to determine whether 

 a cause-and-efFect relation exists between G. brevis 

 and the catastrophic fish kills. Furthermore, 

 studies of such problems as the nutritional require- 

 ments of G. brevis, nature of the toxic substance, 

 role of associated organisms, and effects of physical 

 and chemical factors may be facilitated with the 

 use of bacteria-free cultures since the uncertainty 

 regarding the effects of associated bacteria would 

 be eliminated. 



These laboratory studies in coordination with 

 field studies, will provide a better understanding 

 of why the mass mortalities occur. Such knowl- 

 edge will be helpful in predicting when and where 

 outbreaks may be expected and in determining 

 the feasibility of control measures. 



This report presents the results of our studies 

 on the effects of unialgal and bacteria-free cultures 

 of G. breiis on fish as well as the effects of some 

 bacteria isolated from unialgal cultures of this 

 organism and from waters off the west coast of 

 southern Florida.^ Based upon the results of 

 studies with bacteria-free cultures, we conclude 

 that G. brevis produces the toxic substance (s) 

 responsible for the mass mortality of marine 

 animals associated with blooms of this organism 

 in the Gulf of Mexico. 



' We are indebted to K. T. Marvin, Alice Kitchel, and Jean Gates for 

 assistance in performing (he experiments reported here and to E. L. Arnold 

 and R. S. Wheeler for Identifying the test fish. \ 



469 



