was used per container because either the available fish were too few 

 or the containers were too small to accommodate more. Moreover, 

 duplicate containers were not always used because of limitations 

 imposed by insufficient supply of either test fish or test materials. 

 We have taken special care to record all experimental details, some 

 of which may be of no significance, since they may prove of value 

 to others in reviewing our work. 



Experiment 1. A Simple Test of the Toxicity of 

 Gymnodinium brevis Cultures 



This experiment was conducted to determine whether imialgal 

 G. brevis cultures would kill fish. We used a 3i'-week-old culture, 

 replenished with fresh medium three times weekly, containing 1,8 

 million organisms per liter. Sea water from a lagoon (at the east 

 end of Galveston Island, Texas), the locality where the test fish 

 were collected, served as control material. The test materials were 

 not aerated. One rough silver side (Membras vagrans ) 3^ in. long and 

 one sailfin molly ( Mollienisia latipinna ) 2^ to 3 in. long was placed 

 in each of two 1-liter beakers — one containing sea water, the other 

 G. brevis culture. The beakers were covered with polyethylene 

 sheeting. 



The M. vagrans survived only 4 minutes in the G. brevis culture 

 whereas this species survived 43 minutes in the sea water. The M. 

 latipinna died after 85 minutes exposure to the G. brevis culture 

 and the fish in the sea water was alive when the experiment was 

 discontinued 4 days later. Although the lethality of G. brevis 

 cultures to fish is evident from these results, they do not necessarily 

 prove that a toxic substance is involved. 



Experiments 2 and 3. Comparison of Effects of Gymnodinium brevis 



and Gymnodinium splendens Cultures 



The mere presence of numerous dinoflagellates may have been 

 responsible for the toxicity of the \xnialgal culture used in experiment 

 1. To test this possibility, fish were subjected to unialgal G. brevis 

 and G. splendens cultures in experiments 2 and 3. Experiment 2 was 

 conducted under the same conditions as experiment 1. A 4-week-old 

 unialgal culture of G. . brevie and a 10-week-old unialgal culture of 

 G. splendens containing 2.1 and 2.8 million organisms per liter, 

 respectively, were tested for toxicity to M. latipinna {2^ to 3 in, 

 long). Both cultures were replenished with fresh medi\ira three times 

 weekly during the incubation period. Sea water from which the test 

 fish were taken was used as control. One fish was placed in each 

 of three test materials. The fish in the G. brevis culture died 

 after 47 minutes. In the G. splendens culture and in sea water the 

 fish were alive at the close of the study 19 days later. 



Experiment 3 duplicates experiment 2 in most respects except 

 that the cultures were a week older. At this time there were 2.0 



