476 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE' 



Other test materials included single containers of 

 G. brevis cultures that had been heated to 35° and 

 45° C. 



Each of the 11 containers (4-liter beakers) re- 

 ceived two common killifish {Fundulus grandis), 

 3 to 3K inches long. The test materials, 2 liters 

 in each container, were not aerated. 



Only one of the four fish placed in each of the 

 two control materials, sea water and Prorocentrum 

 culture (bottle 2), failed to survive the 4-hour test 

 period (table 4). On the contrary, the four fish 

 subjected to tlie G. breins culture (bottle 1) died 

 before the end of the test period. The death 

 times were 9, 16, 100, and 130 minutes. Again, 

 however, the G. brevis culture (bottle 1) had a 

 greater bacterial concentration than the material 

 in bottle 2, in spite of the addition of Prorocentrum 

 sp. a month earlier. The count for the former 



was 2.2 to 2.4 million bacteria per ml. in contrast 

 with 0.19 to 0.20 million per ml. for the latter. 

 The count for the material in bottle 2 is quite 

 similar to that obtained for this bottle in experi- 

 ment 5 (table 3). 



The fish lived 20 to 100 minutes in the G. brevis 

 culture heated to 35° C. In the culture heated 

 to 45° C. the death times were only 13 and 18 

 minutes. Three of the four fish exposed to 

 filtrates of a G. breins culture survived the experi- 

 mental period. The two fish subjected to the 

 materials eluted from filter paper through which 

 G. brevis culture had passed died in 23 and 130 

 minutes. Filtration appears to reduce the toxicity 

 of G. brevis cultures; however, other filtering 

 methods must be tested before this effect can be 

 established as a characteristic of filtration. 



Table 4. — Experiment 6: Effects on Fundulus grandis of unialgal cvltures of Gymnodinium brevis and Prorocentrum 



sp., and effects of heating and filtration on toxicity 



[2 flsh tested in each container] 



' Time (hr.:min.) of cessation of opercular movement. 



2 Death did not occur during the 4-hour test period. 



3 The O, brevis-free bacterial culture (bottle 2} was inoculated with unialgal Prorocentrum sp. 1 month prior to e.xperiment. 

 * Another O. brevis culture was used for the heating and filtration studies because of Insufficient culture in bottle 1. 



EXPERIMENT 7. — Comparison of Toxicity of Unialgal Gymnodinium brevis, Prorocentrum sp., and Gymnodinium 

 sp., and Effects of Filtration on Toxicity 



The final toxicity study in this series (experi- 

 ments 4-7) compared the effects of unialgal 

 cultures of Gymnodinium brevis, Prorocentrum sp., 

 and Gymnodinium sp. The two latter organisms 

 were isolated from water samples taken in the 

 lagoon at Galveston, Texas. Gymnodinium sp. is 

 morphologically similar to the cultured forms of 

 G. brevis originally isolated from Florida waters. 

 A portion of the experiment was to determine 



whether passage of G. brevis cultures through a 

 millipore membrane would reduce toxicity as did 

 their passage through filter paper. 



Striped mullet [Mugil cephalus) and variegated 

 minnows {Cyprinodon variegatus) were used as 

 test fish. The mullet (3 to 4 in. long) were main- 

 tained in aerated aquariums about 24 hours before 

 beginning the experiment. The minnows (about 

 Iji in. long), collected 3 days prior to beginning 



