Experiment 7. Comparison of Toxicity of Unialgal Gymnodinimn brevis , 

 Prorocentrum sp., and Gymnodinium sp., and Effects of 

 Filtration on Toxicity 



The final toxicity study in this series was performed to compare 

 the effects of unialgal cultures of G. brevis , Prorocentrum sp., and 

 Gymnodinium sp. The two latter organisms were isolated from water 

 samples taken in the lagoon, Galveston, Texas. Gymnodinium sp. is 

 morphologically similar to the cultured forms of G, brevis originally 

 isolated from Florida waters. A portion of the experiment was to 

 determine whether passage of G. brevis cultures through a mlllipore 

 membrane would reduce toxicity as did passage through filter paper. 



Striped mullet (Mugil cephalus ) and variegated minnows ( Cyprinodon 

 variegatus ) were used as test fish. The M. cephalus (3 to L, in. long) 

 were maintained in aerated aquaria about 24- hours before beginning 

 the experiment. The C. variegatus (about '\.\ in. long), collected 

 3 days prior to beginning of experiment, were kept in a non-aerated 

 aquarium since this species survives well without aeration. 



Five of the seven different test materials included in this 

 study were tested in duplicate. These materials consisted of: two 

 different unialgal G. brevis cultures (containers 1 and 2, 3 and 

 <+); Gymnodinium sp. (containers 5 and 6); Prorocentrum sp. (containers 

 7 and 8); and culture medium from bottle 3 (containers 9 and 10). 

 Also included was a filtrate prepared by passing 1 liter of G. brevis 

 culture through a millipore membrane (container 11) and the residues 

 retained with this membrane eluted in 1 liter of culture medium from 

 bottle 3 (container 12). The millipore membrane (HA) retains particles 

 as small as 0.5 micron. Each of the 12 containers (2-liter beakers) 

 received approximately 1 liter of test material which was not aerated. 



Before adding the fish, bacterial samples were taken from two 

 containers of G. brevis culture (1 and 2) and one container of 

 culture medium (9). These containers were arbitrarily selected 

 in order to compare the bacterial counts in come of the containers 

 before adding the fish with those obtained after death of the test 

 fish. The samples for bacterial counts were refrigerated from 3 to 

 3-2/3 hours before preparing poiir -plates. All containers with 

 dinoflagellates (l through 8) as well as the filtrate of the 

 G. brevis culture (container 11) were sampled for counts of these 

 organisms just before adding the fish. These counts weire completed 

 within 3 hours after collection of samples. 



One M. cephalus was placed in each of the 12 containers. 

 Each M. cephalus was removed from its container shortly after 

 death and a C. variegatus was added. The fish were not introduced 

 simultaneously since the M. cephalus were rather large for the 

 containers. 



16 



