478 



FISHERY BULLETIN OF THE FPSH AND WILDLIFE SERVICE 



per ml. obtained for 6. brevis cultures. M. 

 cephalus in the Prorocentrum culture survived 

 nearly 7 hours. Those exposed to Gymnodinium 

 sp. died after 46 and 69 minutes. 



Cyprinodon van'egatus survived considerably 

 longer than M. cephaluf! in all test materials. In 

 G. brevis cultures the death times for C. variegatus 

 varied from 2?^ to 7-8 hours. This species survived 

 the 27-hour test period in the two control materials 

 (the culture medium and the Prorocentrum 

 culture). C. variegatus lived about 2}^ and 2% 

 hours in Gymnodinium sp. culture. 



M. cephalus lived only 14 minutes in the milli- 

 pore filtrate of the G. brevis culture, in contrast 

 with 53 minutes in material eluted from the milli- 

 pore membrane. Likewise the filtrate was more 

 to.xic than the residues to C. variegatus: the fish 

 Hved 4K hours in the filtrate, whereas the fish in 

 the residues survived the test period. 



RESULTS OF EXPERIMENTS WITH UNIALGAL 

 CULTURES 



The fish subjected to unialgal cultures of G. 

 brevis, with the exception of one fish, died more 

 rapidly than those exposed to control materials 

 in the seven experiments considered in this sec- 

 tion. The greater survival of the control fish 

 demonstrates that unialgal cultures of this or- 

 ganism are toxic to the five species of fish tested 

 {Membras vagrans, Mugil cephalus, Fundulus 

 grandis, Cyprinodon variegatus, and Mollienisia 

 latipinna). Indeed, the rapidity with which the 

 fish succumbed in some of the cultures emphasizes 

 the toxicity of unialgal G. brevis cultures. For 

 example, the minimum death times for some of 

 these fish were 4 minutes for M. vagrans (only 1 

 fish tested), 14 to 16 minutes for M. cephalus, and 

 9 to 16 minutes for 7^. grandis. However, all five 

 species did not show such extremes of sensitivity 

 to G. brevis cultures. The minimum death times 

 for C. variegatus were 2)i to 2% hours. 



The concentration of G. brevis in the cultures 

 used for the seven experiments varied from 0.6 to 

 2.1 million per liter. Since these cultures were 

 not free of bacteria, such organisms possibly con- 

 tributed to their to.xicity. 



The results of a preliminary study suggest that 

 the survival period after exposure to G. brevis de- 

 pends on the length of exposure and that fish 

 subjected for just a few minutes may not recover 

 when transferred to sea water. M. cephalus, sub- 



jected to unialgal G. brevis for 3 and 15 minutes 

 and then transferred to sea water, lived for 165 

 and 12 minutes, respectively (experiment 5). 



Moreover, there is some suggestion that G. 

 brevis cultures may become more toxic with each 

 subsequent addition of test fish. For example, 

 in experiment 5, the death times of each of four 

 M. cephalus added in succession to the same culture 

 decreased progressively from 29 to 7 minutes. 

 We do not know the reason (s) for this apparent 

 increase in toxicity. Since the test materials 

 were not aerated, possiblj^ the o.xygen content 

 was progressively lowered by the test fish and 

 the death times decreased thereby. 



The toxicity of unialgal G. brevis cultures does 

 not depend on the presence of living organisms. 

 Cultures heated to 35° and 45° C. were no less 

 toxic than the untreated ones. The removal of 

 G. brevis from a culture by millipore filtration did 

 not reduce the toxicity. The relative toxicity of 

 a filtrate appears to be dependent upon the type 

 of filter membrane employed. A paper membrane 

 (Whatman No. 42) apparently retains the more 

 toxic portion of the culture. 



Attempts to determine whether G. brevis or its 

 associated bacterial flora produces the toxic sub- 

 stance were not entirely successful. G. brevis -iree 

 cultures presumed to contain the bacterial flora 

 associated with unialgal cultures of this organism 

 were not to.xic to the test fish. However, when 

 these experiments were performed, the bacterial 

 counts of these cultures were considerably lower 

 than those of the G. brevis cultures. Nevertheless, 

 a culture of presumed associated bacteria with a 

 count of slightly more than a million per ml. 

 proved nontoxic to M. cephalus. The bacterial 

 count of this culture in experiment 4 (table 2) was 

 comparable to those of the unialgal cultures that 

 were toxic to M. cephalus and C. variegatus in 

 experiment 7 (table 5). Furthermore, in experi- 

 ment 7 uninoculated culture medium containing 

 about 2 million bacteria per ml., which was slightly 

 higher than the counts of two different G. brevis 

 cultures, was not toxic to the test fish. 



Unialgal cultures of three species of dinoflagel- 

 lates {Gymnodinium splendens, Gymnodinium sp., 

 and Prorocentrum sp.) isolated from the lagoon, 

 Galveston, Texas, were tested for toxicity to fish. 

 Two species proved nontoxic and one toxic. The 

 nonto.xic forms, G. splendens and Prorocentrum 

 sp., were used in concentrations comparable to 



