492 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



discolored after the addition of 2 to 4 million 

 F. piscicida per ml., whereas in Bein's studies 



the water was bright orange-yellow 24 hours 

 after it received the bacterial cultures. 



GENERAL DISCUSSION 



The well-established association of Gym.nodi- 

 nium hrevis with the sporadic mass mortality of 

 fish and other marine animals that has occurred 

 in the Gulf of Mexico since 1947, in conjunction 

 with the clear-cut laboratory demonstration that 

 this dinoflagellate in pure culture is toxic to fish, 

 leaves no reasonable doubt that this organism 

 causes these mortalities. Considering this evi- 

 dence, we propose the name "brevis red tide" for 

 such mortalities instead of the nonspecific term 

 "red tide" that is used commonly in popular and 

 scientific writing. In our opinion, ample character- 

 istics properly identify these mass mortalities 

 occurring in the Gulf of Mexico as a distinct 

 phenomenon. This phenomenon can be diagnosed 

 by the presence of G. hrevis in the waters in which 

 fish and other marine animals are dying. An 

 additional diagnostic characteristic is the odorless, 

 human-respiratory-tract irritant often present in 

 or near mortality areas where droplef.i of sea 

 water become air-borne as a result of wind, wave 

 action, et cetera (Galtsoff 1948; Gunter et al., 1948; 

 Woodcock 1948; Ingle 1954; and others). 



Failure to find either one or both of the men- 

 tioned diagnostic characteristics in an isolated 

 area of dead or dying fish would not necessarily 

 eliminate G. hrevis as the cause. At least four 

 possible reasons support this statement: (1) The 

 conditions or agents required to make droplets of 

 sea water air-borne may be absent. (2) Dead fish 

 may drift or be carried into an area either unsuit- 

 able for the survival of G. hrevis or removed from 

 the bloom. (3) An isolated mass of water in 

 which G. hrevis is blooming may suddenly become 

 unsuitable for this organism and yet not lose its 

 toxicity to fish until sometime later. Experimental 

 evidence supports this suggestion, since the re- 

 moval of living G. hrevis from cultures by millipore 

 filtration or the killing of the organisms with 

 gentle heat did not inactivate the toxic substance. 

 A specific diagnostic test for the toxic substance (s) 

 produced bj- this organism would be helpful in 

 diagnosing the cause of mortality in such cases. 

 G. hrevis is so delicate that under adverse con- 

 ditions it may die within a matter of minutes, 

 leaving only fragmentary remains that are not 



readily identifiable. (4) The fish may contact the 

 toxic substance in a bloom of G. hrevis in one area 

 and yet not succumb until it moves into an area 

 where the organism is not flourishing. This possi- 

 bility is based on limited observations that fish, 

 exposed to G. hrevis cultures for short periods and 

 removed before they showed distress, died after 

 being placed in sea water. The death time after 

 removal to sea water appears to decrease as the 

 exposure time is increased. 



The results of our studies support Galtsoff's 

 (1948) conclusion that fish are not killed by clogging 

 of the gill filaments by masses of G. hrevis. The 

 available evidence makes untenable the view that 

 fish suffocate as a result of mechanical occlusion 

 of gill surfaces by the mere presence of large num- 

 bers of organisms. Results of the studies with 

 both heated and filtered G. brevis cultures, tests 

 with other dinoflagellate cultures, and oxygen 

 analyses of G. hrevis cultures emphasize the exist- 

 ence of a toxic substance(s). G. hrevis cultures 

 heated to 35° and 45° C. did not lose their toxicity 

 although the organisms were disrupted. Like- 

 wise, the removal of this organism (both unialgal 

 and bacteria-free) by millipore filtration did not 

 detoxicate the cultures. Unialgal cultures of G. 

 splendens and Prorocentrum sp. were nontoxic 

 despite the fact that the number of organisms 

 compared to and even, in some cases, exceeded 

 the concentrations in the toxic G. hrevis cultures. 



Filtrates of G. hrevis cultures are toxic; how- 

 ever, the method of filtration determines whether 

 the more toxic portion of the culture wiU pass 

 through or be retained by the filter membrane. 

 In our studies conducted with both unialgal and 

 bacteria-free cultures, the filter-paper residues 

 eluted in either sea water or culture medium were 

 more toxic to the fish than were the filtrates. The 

 results were reversed when a culture was passed 

 through a millipore membrane under suction: 

 the more toxic portion passed through the mem- 

 brane. The reasons for the different effects of 

 these two methods of filtration are not known. 

 The filter materials differ in composition and size; 

 the miUipore membrane (diameter 47 mm.) is 

 made of cellulose esters, whereas the filter paper 



