UNIALGAL AND BACTERIA-FREE CULTURES OF G. BREVIS 



481 



T.\BLE 6. — Experiment 8: Effects of bacteria-free and unialgal cultures of Gymnodinium brevis on Mugil cephalus and 



Cyprinodon variegatus 



 [AH containers received 2 flsh of each species eicept No. 2, In which 3 M. cephalua were tested] 



' Determinations of pH made on samples withdrawn directly from culture 

 vessel. All containers aerated except as noted. 



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



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



* The first G. brevis and bacterial counts listed for each container were 

 obtained from samples collected before introduction of the fish. Samples 

 for second counts, in parentheses, were taken immediately after the death 



The samples taken for the initial bacterial counts 

 were refrigerated from 1 hour to nearly 3 hours 

 before preparation of the pour-plates. Most of 

 the G. brems counts were completed within a few 

 minutes to an hour after withdrawal of the 

 samples. A few samples, however, stood for a 

 maximum of approximately 3 hours. 



Each of the 14 containers received two M. 

 cephalus and two C. variegatus except the con- 

 tainer (2) of sea \i^ater, which received three 

 M. cephalus. Each fish was removed from the 

 container shortly after it died so that test materials 

 would not become excessively fouled by decom- 

 posing fish. 



After commencing the experiment, samples 

 were again taken for G. brevis and bacterial counts. 

 Seven of the containers with G. brevis were sampled 

 for counts of this organism immediately after 

 the death of the last fish in the container. Two 

 other containers (12 and 13) of G. brevis, in which 

 the last fish in the container survived beyond 

 8 hours, were sampled about 8 hours after begin- 

 ning the experiment. The second set of samples 

 for bacterial counts was taken either immediately 

 after the death of the last fish in the container 



of la's! flsh in container, except for two G. brevis counts (containers 12 and 13) 

 and four bacterial counts (containers 2, 5, 11, and 12): the former were taken 

 about 8 hours and the latter 30 to 3U2 hours after start of experiment. 



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



• The last fish (C. variegatus) in container 12 died about 30 minutes after 

 close of experiment. 



or after 30 to 31}^ hours, provided that one fish 

 survived the test period (3 1)2 hours). The 10 

 containers sampled for bacterial counts included 

 all of those that were sampled for such counts 

 initially (containers 3, 5, 6, 9, 11, and 12), the 

 container (1) of unialgal G. brevis, the container 

 (2) of sea water, and the two containers (4 and 7) 

 of nonaerated G. brevis cultures. These samples 

 were plated after 15 to 90 minutes' refrigeration. 



Following the collection of bacterial and G. 

 brevis samples, all test materials were sampled 

 for dissolved oxj^gen, pH, and salinity determina- 

 tions (table 7). Aeration of each container (if 

 aerated) was discontinued just before collection 

 of the samples, which were taken cither imme- 

 diately after the death of the last fish in the 

 container or near the end of the experimental 

 period if at least one test fish survived. Seven 

 containers (2, 5, 8, 11, 12, 13, and 14), those in 

 which at least one fish survived beyond 7 hours, 

 were also sampled for pH determinations 7 to 

 7% hours after start of the study. During this 

 31}^-hour experiment, room temperature varied 

 from 20° to 24.5° C. 



