Unialgal cultures of three species of dlnof lagellates ( Gym - 

 nod inium splendens , Gymnod inium sp., and Prorocentrum sp.) isolated 

 from the lagoon, Galveston, Texas, were tested for toxicity to 

 fish. Two species were non-toxic and one proved toxic. The non- 

 toxic forms, G. splendens and Prorocentrum sp,, were used in 

 concentrations comparable to and, in some cases, even exceeding 

 those of the toxic G. brevis . In fact, M. cephalus survived 

 considerably longer in the Prorocentrum culture than in the control 

 material (uninoculated culture medium) in experiment 7 (Table 5). 

 The Prorocentrum possibly aided survival of the fish by liberating 

 oxygen since the test materials were not aerated. The Gymnod inium 

 sp. was toxic to M. cephalus and C. variegatus (Table 5). In view 

 of these results and since this organism in culture is morphologically 

 similar to G. brevis , we tentatively consider the Galveston Gymnod inium 

 to be G. brevis . The Galveston Gymnod inium was observed only th-ree 

 times (all within the same week) although samples were collected 

 from the lagoon three times weekly during an 11-month period. The 

 concentrations in the lagoon samples varied form 1,000 to 60,000 

 organisms per liter. 



EXPERIMENTS WITH BACTERIA-FREE CULTURES OF GYMNODINIUM BREVIS 



Mass bacteria- free cultures of G. brevis were established 

 following the completion of experiment 7. The two experiments 

 to follow (8 and 9) were the first toxicity tests to be conducted 

 with pure cultures. The importance of these studies lies in the 

 fact that the observed effects can be attributed to G. brevis with 

 certainty since no other organisms were present during the incuba- 

 tion period. Substantiation of the toxicity of unialgal G. brevis 

 with bacteria-free G. brevis should establish the existence of a 

 cause and effect relationship between "blooms" of this organism 

 and associated mass mortality of marine animals. The experiments 

 with bacteria-free cultures were more refined in several respects 

 than those with unialgal cultures. In addition to aerating most 

 of the test materials, such factors as temperature, dissolved oxgen, 

 salinity, and pH of these materials were determined. 



Experiment 8. Effects of Unialgal and Bacteria-free 

 Gymnod inium brevis Cultures 



The first mass bacteria-free cultures of G, brevis were tested 

 for toxicity to striped mullet ( Mugil cephalus ) and variegated minnows 

 ( Cyprinodon variegatus ) . The C. variegatus (1-J to l|- in, long) and 

 M. cephalus (1 to I4: in. long) were maintained in aerated aquaria for 

 5 days and overnight, respectively, before beginning of experiment. 

 One liter of distilled water was placed in each 2-liter beaker, 

 containers for the various test materials, 5 days before commencing 

 the experiment so that the aeration equipment could be tested and 

 adjusted. The water was discarded and the beakers received no 

 further treatment before introducing the various test materials. 



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