culture had a bacterial count of 2.7 million per ml — about 50^ 

 greater than that of the G. bre vis -free bacterial culture. The 

 validity of some bacterial counts is questionable because of prolonged 

 refrigeration of samples before preparing the plates. They indicate, 

 however, the relative number of bacteria in the three bottles at the 

 various sampling intervals. Although bottles 1 and 2 apparently 

 were inoculated with the same bacterial flora, we' can only" presume 

 that the floras subsequently developing in these bottles were 

 qualitatively comparable . 



Approximately 6 weeks after inoculating bottles 1 and 2, materials 

 from these bottles and the reservoir (bottle 3) in addition to an 

 11-month-old unialgal G. brevis culture and centrifuged sea water were 

 used to conduct experiment 4-. One striped mullet (Mugil cephalus ) 2-2 

 to 3 inches long was subjected to each of the five different nonaerated 

 test materials, 750 ml in 1-liter beakers. We observed the fish 

 closely and recorded the time at which they began to show imbalance 

 ("distress time") and the time at which they showed no visible opercular 

 movement ("death time"). Bacterial-count samples were obtained from 

 each container before the fish was added. These samples were 

 refrigerated 1 to 1^ hours before plating. 



The results (Table 2) of this 24.-hour experiment show that the 

 fish in the two unialgal G. brevis cultures died in 50 minutes and 2-^ 

 hours. Two of the three control fish survived considerably longer, 

 7^ hours in the G. bre vis -free bacterial culture and the entire test 

 period in the uninoculated culture medium. However, the fish in the 

 centrifuged sea water died after 58 minutes. The early death of this 

 control fish was perhaps due to injury. 



The bacterial count of 6.0 million per ml for the G. brevis culture 

 (bottle l) in container 3 was five times greater than that for the 

 G. bre vis -free bacterial culture (bottle 2) in container 4-' Prior to 

 this 6-week check the bacterial counts of these two cultures were 

 comparable (Table l). The disparity in the bacterial counts for 

 experiment 4- necessitated additional studies in order to determine 

 the toxicity agent in unialgal G. brevis cultures. 



Experiment 5 . The Effects of Unialgal Gymnodinium brevis 

 Cultures, the Associated Bacterial Flora, and Unialgal 

 Prorocentrum sp. Cultures 



In addition to testing the effects of G. brevis culture (bottle 1) 

 and G. bre vis -free bacterial culture (bottle 2), another dinoflagellate, 

 prorocentrum sp., was tested for toxicity to fish in the second experi- 

 ment of this series. This organism was isolated from the lagoon, 

 Galveston, Texas . The materials in bottles 1 and 2 were 3j months 

 old at this time. Freshly collected sea water served as control. 

 The four different materials, 2 liters of each in 4.-liter beakers. 



10 



