474 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE' 



Table 1. — Experiments 4, 5, 6, and 7: Bacterial counts of 

 samples taken from study bottles at irregular intervals 



' The value of 12 million bacteria per ml. for the reservoir appears to be 

 excessively high when compared with the other counts obtained at either 

 earlier or later intervals. With the exception of the presently considered 

 value, the highest bacterial count obtained from the reservoir was 1.8 million 

 per ml. (table 5, experiment 7). 



4. One striped mullet (Mugil cephalus), 2% to 3 

 inches long, was subjected to 750 ml. of each of 

 the five different nonaerated test materials 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 ob- 

 tained from each container before the fish was 

 added. These samples were refrigerated 1 hour 

 to 1^ hours before they were plated. 



The results (table 2) of this 24-hour experiment 

 show that the fish in the two unialgal G. hreeis 



cultures died in 50 minutes and 2){ hours. Two of 

 the three control fish survived considerably longer, 

 7K hours in the G. brems-iree 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. breins culture (bottle 1) in container 3 was 

 five times greater than that for the G. brevis-hee 

 bacterial culture (bottle 2) in container 4. Prior 

 to this 6-week check the bacterial counts of these 

 two cultures were comparable (table 1). Dis- 

 parity in the bacterial counts for experiment 4 

 necessitated additional studies in order to deter- 

 mine the toxicity agent in unialgal G. brevis 

 cultures. 



Table 2. — Experiment 4: Effects on Mugil cephalus of 

 unialgal Gymnodinium brevis cultures and of a G. brevis- 

 free culture presumed to contain bacteria associated with 

 this organism in unialgal cultures 



1 Time (hr.:min.) required for fish to show first signs of imbalance. 

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

 3 Distress or death did not occur during the 24-hour test period. 

 * Not known. 



EXPERIMENT 5. — Effects of Unialgal Gymnodinium brevis Cultures, Associated Bacteria, and Unialgal Proro- 

 centrum sp. Cultures 



In addition to testing the effects of G. brevis 

 culture (bottle 1) and G. breds-hee bacterial 

 culture (bottle 2), another dinoflagellate, Proro- 

 centrum sp., was tested for toxicity to fish in the 

 second experiment of this series. This organism 

 was isolated from water samples taken in the 

 lagoon, at Galveston, Texas. The materials in 

 bottles 1 and 2 were '3% months old at this time. 

 Freshly collected sea water served as control. 

 The four different materials, 2 liters of each in 



4-liter beakers, were tested in duplicate for 

 toxicity to Mugil cephalus (2^ in. long). One 

 fish was tested in each container without aeration. 

 Samples were collected from each container for 

 bacterial counts before the fish was added. 

 These samples were plated after IK to 5 hours' 

 refrigeration. 



The test fish subjected to the G. breds culture 

 died within an hour (29 and 47 minutes) whereas 

 the fish in the other test materials lived a mini- 



