in 15 and 25 minutes in contrast to 69 and 72 minutes in container 

 10. However, C. variegatus , a less sensitive fish than M« cephalus , 

 showed more similarity of "death times": 3 hours and 51 minutes and 

 4- hours and 58 minutes in container 9, 3 hours and 4^4 minutes and 

 5 hoiirs and 54 minutes in container 10. 



Another anomaly in experiment 8 is the case in which one pure 

 culture (container 12) with a G. brevis count of 3.4 million per 

 liter was less toxic to both M. cephalus and C. variegatus than the 

 duplicate culture (container 13) whose count was 2.3 million organisms 

 per liter. The "distress times" (about 4^ hours) and "death times" 

 (about 42 hours) for M. cephalus in the more concentrated G, brevis 

 cultuj'e (container 12) were approximately 2 hours greater than such 

 times in the less concentrated duplicate culture (container 13). 

 The "distress times" and "death times" for the C. vajiegatus in 

 each culture were not as uniform, as in case of the M, cephalus . 

 Nevertheless, they show that the cultui'e in container 13 was more 

 toxic to _C. variegatus than the one in container 12; the fish died 

 after about $ and 15 hours in the former and after about 27 and 32 

 hours in the latter container. 



We realize that due to variations in the condition of the 

 individual test fish some will survive longer than others when sub- 

 jected to toxic agents. It is our opinion, however, that the over -all 

 uniformity in the response of the test fish within each individual 

 container, especially in experiment 8, is a strong indication of 

 other subtle variables of which we have no knowledge. 



Despite the evidence that our toxicity studies require more 

 standardizing, the results of all experiments reported herein 

 indicate that the sensitivity of fish to G. brevis cultures is 

 variable. Our tests included six species of fish as follows: 

 Membras va grans , Mugil cephalus , Fundulus grandis , Mollienisia 

 latipinna . Fundulus similis . and Cyprinodon variegatus . Possibly 

 the most sensitive of these fish is M. vagrans ; the only indi- 

 vidual tested died in 4 minutes. M„ cephalus , the species used 

 in the greatest nimber of experiments (5), showed "death times" 

 varying from a minimum of 8 minutes to a maximion of 4~3/4 hours. 

 The great majority of them died within an hour. Small M. coph-alus 

 (l to 1^ in, long) are possibly slightly less sensitive to G. 

 brevis cultures than large M. cephalus (42 "to 5-2 in. long). This 

 possibility is suggested by results of experiment 9 (Table 8); 

 the large M. cephalus in each container of ^onfiltered Go brevis 

 culture, without exception, died before any of the three 

 accompanying small M» cephalus . In some cases the first small 

 mullet died within 3 to 5 minutes after the large mullet; in 

 other cases the first small mullet died 20 to 70 minutes later. 

 The F. gra.ndis showed about the same degree of sensitivity as 

 M. cephalus minimum "death time" 9 minutes, maximium "death time" 



46 



