Immediately after the M, cephalus died in the containers 

 which were initially sampled for bacterial counts (1, 2, and 9), 

 these containers were again sampled for such counts o Such samples 

 were also taken from one of each of the remaining duplicate test 

 materials (containers 3, 5, and 7) and from the millipore filtrate 

 (container 11) following the death of the Mo cephalus „ Pour- 

 plates were prepared with these samples after 4 "t'O 'oz hours 

 refrigeration, except the sample from container 7 which was 

 stored only 1-1/3 hour's. 



The results (Table 5) of this 27-hour experiment show that 

 all of the M. cephalus subjected to either G„ brevis cultures 

 or filtrate and residues of such a culture died in less than an 

 hour. The "death times" varied from 14 to 53 minutes „ The 

 M. cephalus in the uninoculated culture medium lived approximately 

 2-1/3 and 3 hours. The bacterial count of 1,8 million per ml 

 of this culture medium (bottle 3) was higher than the 1,0 to 1„5 

 million per ml obtained for the G,^ brevis cultures. The M. 

 cephalus in the Prorocentrum culture survived nearly 7 hours. 

 Those exposed to the Gymnodinium sp, died after 46 and 69 minutes. 



The C.. variegatus survived considerably longer than the 

 M. cephalus in all test materials. In the G, brevis cultures 

 the "death times" for C. variegatus varied from 2-2/3 to 7-8 hours. 

 This species survived the 27-hour test period in the two control 

 materials (the culture medium and the Prorocentrum culture). The 

 C, variegatus lived about 2-1/3 and 2-2/3 hours in the Gymnodinium 

 sp, culture. 



M. cephalus lived only I4 minutes in the millipore filtrate 

 of the Go brevis cultirre in contrast to 53 minutes in material 

 eluted from the millipore membrane. Likewise the filtrate was 

 more toxic to C. variegatus than the residues; the fish lived 

 42" hours in the former material whereas the one in the latter 

 survived the test period. 



Discussion of Results of Experiments with Unialgal Cultures 



The fish subjected to unialgal cultures of G, brevis died 

 more rapidly than those exposed to control materials in the seven 

 experiments considered in this section, excepting one fish. The 

 greater survival of the control fish demonstrates that unialgal 

 cultures of this organism are toxic to the five species of fish 

 tested ( Membras vagrans , Mugil cephalus , Fundulus grandis , Cyprinodcn 

 variegatus , and Mollienisia latipinna ). Indeed, the rapidity with 

 which the fish succumbed in some of the cultures emphasizes the 

 toxicity of unialgal G. brevis cultures. For example, the minimum 

 "death times" for some of these fish were: 4 minutes for M, vagrans 

 (only one tested), I4 to 16 minutes for Mo cephalus , and 9 to 16 



17 



