2 hours and 10 minutes. The Mollienisia latlpinna died in a 

 minimum of -47 minutes and a maximum of 85 minutes, C.. variegatus 

 is probably the least sensitive of the six species tested. The 

 minimum "death time" was about 2-1/3 hours, the maxim.um was 32 

 hours. The sensitivity of F. similis is possibly comparable to 

 that of C. variegatus . Two F. sim.ilis died in l^ and 10 to 19 

 hours. 



A chromogenic bacterium, Flavobacterium piscicida , has bean 

 suggested as a possible cause of the mass fish kills and associated 

 sea water discolorations occurring along the west coast of Florida 

 (Bein, 1954). Bein found that this bacterium was toxic to several 

 species of fish although he did not indicate the bacterial concen- 

 trations employed. In our tests Mugil cephalus were not affected 

 by initial concentrations of 2 million or more F, piscicida per ml. 

 Contrary to Bein's experience, F. piscicida apparently did not grow 

 in our experiment and possibly lived only a short time after being 

 added to the test medium (sea water). We could scarcely detect this 

 bacterium at the end of the 5-day test period. A "red bacteriiim" 

 which we isolated from G. brevis -infested water off the west coast 

 of Florida appears to be toxic to fish. Concentrations of the order 

 of 0.5 to 2 million bacteria per ml were toxic to Fi-indulus similis . 

 The "red bacterium" has not been encountered in an abundance to 

 implicate it as a fish-killing agent. Thus far, neither the 

 association of chromogenic bacteria with extensive fish kills nor 

 the natural existence of toxic concentrations of such bacteria has 

 been established. In the case of G?/mnodinium brevis both of these 

 conditions have been well established. 



SIMMAB,Y AND CONCLUSIONS 



1. Since 1947 "blooms" of the dinoflagellate, Gymnodinium brevis , 

 have been associated with sporadic mass mortalities of marine animals 

 and discolored water In the Gulf of Mexico. Extensive laboratory 

 studies conducted with unialgal and bacteria-free cultures as well 



as related bacterial studies offer overwhelming evidence that 

 "blooms" of this organism are the direct cause of the associated 

 mortalities. 



2. Bacteria-free cultures of G. brevis with concentrations 

 varying from 2.3 to 4.8 million organisms or liter were toxic to 

 three species of test fish. Five species of fish were killed when 

 subjected to unialgal G. brevis cultures containing 0.6 to 2,1 

 million organisms per liter. The numbers of G. brevis in areas of 

 natural fish kills often greatly exceed these toxic laboratory 

 concentrations . 



47 



