THE EFFECTS OF UNIALGAL AND BACTERIA-FREE CULTURES OF GYMNODINIuM 

 BREVIS ON FISH AND NOTES ON RELATED STUDIES WITH BACTERIA 



By 



S. M. Ray and William B. Wilson 

 INTRODUCTION 



The association of the dinoflagellate Gymnodinium brevis 

 Davis with the mass mortality of marine animals occurring sporadi- 

 cally in the Gulf of Mexico is well established (Davis, 194-8; 

 Galtsoff, 1948 and 1949; Gunter et al., 19-48; Wilson and Ray, 

 1956; Woodcock, 1948, et al.)« Indirect evidence presented in 

 these papers strongly supports the contention that G. brevis . 

 is the cause of fish kills, commonly referred to as red tides-=( 

 when its concentration reaches the order of hundreds 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 (l) the presence of dead or dying fish in water 

 containing such concentrations of G. brevis , (2) laboratory demon- 

 stration that water containing great numbers of G. brevis is toxic 

 to fish, and (3) demonstration that substances toxic to fish may 

 be extracted from water infested with G^ brevis . Further evidence 

 of a more direct natiire is provided by the demonstration that 

 unialgal cultures of G. brevis are toxic to fish (Wilson and Col- 

 lier, 1955). 



The development of stock unialgal cultures of G. brevis 

 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 handicapped since the suspected 

 causative agent was unavailable for study except during outbreaks. 

 Even then, their material was limited to raw samples from the 



1/ The term "red tide" is generally applied to discolored sea water 

 regardless of either causes or consequences, i.e., the causes 

 of the discolorations may vary from "blooms" of many different 

 microorganisms to nonliving agents such as iron compounds; and 

 the mortality of animals, especially fish, may or may not be as- 

 sociated with such discolorations. 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 "brevis red tide" be applied to the mass 

 mortality of marine organisms associated with Gymnodinium brevis . 



