A 24.-hour pure culture of the "red bacterium" was tested for 

 toxicity to F. simllls as a part of the studies dealing with bacteria 

 Isolated from unlalgal G. brevls cultures. Two fish were tested In 

 each of the four containers of test material In which the bacterial 

 count varied from approximately 0.5 to 1 million per ml. The 

 bacterial culture gave a pink tint to the test materials. All eight 

 fish died within 2 to 8 hours. After the last fish died in each of 

 the four containers, samples were taken for bacterial counts. The 

 red colonies in the plates prepared with 0.02 to 0.03 ml of these 

 samples were so abundant that enumeration was impossible. We 

 believe that the minimum concentrations were of the order of 1 to 

 2 million "red bacteria" per ml at the time the last fish died. 



A 6-month-old unlalgal G. brevls culture (replenished with 

 fresh medium about three times weekly) containing 1.3 million 

 organisms per liter killed the test fish less rapidly than cul- 

 tures of the "red bacterium". In the G. brevls culture one fish 

 died after l\ hours and the other one died after 10 to 19 hours. 

 These "death times" appear relatively long when compared with the 

 usual "death times" of fish subjected to other unlalgal cultures. 

 These results may mean either that F. simllls is less sensitive to 

 unlalgal cultures than other fish tested thus far or that this 

 culture was less toxic than the others . 



Flavobacterium piscicida Bein 



A chromogenlc bacterium was isolated by Reuben Lasker (Bein, 

 1954) from a pooled water sample collected after the occurrence of 

 a fish kill associated with discolored water In Whitewater Bay on 

 the southwest tip of Florida. Bein (195<4) found that 24. -hour 

 cultures of this bacterium, which he named Flavobacterium piscicida , 

 killed several species of marine fish. He gave no quantitative 

 values concerning the concentration of bacteria used other than 

 that 500 ml of a 24.-hour culture of this species grown in a 

 0.1^ peptone solution in aged sea water were added to 4 gallons 

 of continuously aerated sea water. After 24 hours all fish 

 in the experimental aquaria died and the water exhibited a bright 

 orange-yellow discoloration. 



We attempted to estimate the minimum number of F. piscicida 

 required to kill mullet ( Mugil cephalus ) since we desired to know 

 what concentration of this bacterium might be required to kill 

 fish under natural conditions. The Marine Laboratory of the 

 University of Miami provided the stock from which our cultures were 

 derived. Since Bein gave no indication of the amount of inoculum 

 used to seed the medium to obtain the 24-hour test cultures, we 

 could not duplicate his inoculation procedures . 



In our experiment, 24-hour cultures were obtained by inoculating 

 two loops of culture removed from a 24-hour slant culture {l% peptone 



38 



