494 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



treated in the same manner throughout the study. 

 For example, in experiment 8 (tables 6 and 7), 

 container 9 received one of the duplicate pure 

 cultures and container 10 received the other. 

 The G. brevis counts of the material in the two 

 containers and such measured factors as pH, 

 dissolved oxj'gen, and salinity were comparable. 

 The similarity between the two containers is 

 further emphasized by the distress times for 

 Mugil cephalus — 10 and 12 minutes in container 

 9, and 13 minutes for each of the two fish in 

 container 10. Despite all these similarities, M. 

 cephalus in container 9 died in 15 and 25 minutes 

 in contrast with 69 and 72 minutes in container 10. 

 However, Cyprinodon variegatus, a less sensitive 

 fish than M. cephalus, showed more similarity of 

 death times: 3 hours 51 minutes and 4 hours 

 58 minutes in container 9, and 3 hours 44 minutes 

 and 5 hours 54 minutes in container 10. 



Another anomaly in experiment 8 is the case 

 in which one pure culture (container 12) with a 

 G. brevis count of 3.4 million per liter was less 

 toxic to both M. cephahis and C. variegatus than 

 the duplicate culture (container 13) in which the 

 count was 2.3 million organisms per liter. The 

 distress times (about 4)^ hours) and death times 

 (about 4K hours) for M. cephalus in the more- 

 concentrated G. brevis culture (container 12) were 

 approximately 2 hours greater than such times 

 in the less-concentrated duplicate culture (con- 

 tainer 13). The distress times and death times for 

 C. variegatus in each culture were not as uniform 

 as in the case of M. cephalus. Nevertheless, they 

 show that the culture in container 13 was more 

 toxic to C. variegatus than the one in container 12: 

 the fish died after about 8 and 15 hours in the 

 former container and after about 27 and 32'hours 

 in the latter. 



We realize that due to variations in the condi- 

 tion of the individual test fish some will survive 

 longer than others when subjected to toxic agents. 

 It is our opinion, however, that the over-all 

 uniformity in the response of the test fish within 

 each individual container, especially in experi- 

 ment 8, is a strong indication of other subtle 

 variables of which we have no knowledge. 



Despite the evidence that our toxicity studies 

 require more standardizing, the results of all 

 experiments reported here indicate that the sensi- 

 tivity of fish to G. brevis cultures is variable. Our 

 tests included six species of fish as follows: 



Membras vagrans, Mugil cephalus, Fundulus gran- 

 dis, Mollienisia latipinna, Fundulus similis, and 

 Cyprinodon variegatus. Possibly the most sensi- 

 tive of these fish is A/, vagrans; the only individual 

 tested died in 4 minutes. M. cephalus, the 

 species used in the greatest number of experiments 

 (5), showed death times varying from a minimum 

 of 8 minutes to a maximum of 4% hours. The 

 great majority of them died within an hour. 

 Small M. cephalus (1 to 1^4 in. long) are possibly 

 slightly less sensitive than large M. cephalus 

 (iYi to dYi in. long) to G. brevis cultures. This 

 possibility is suggested by results of experiment 9 

 (table 8); the large M. cephalus in each container 

 of unfiltered G. brevis culture, without exception, 

 died before any of the three accompanying small 

 M. cephalus. In some cases the first small mullet 

 died within 3 to 5 minutes after the large mullet; 

 in other cases the first small mullet died 20 to 70 

 minutes later. F. grandis showed about the same 

 degree of sensitivity as M. cephalus — minimum 

 death time 9 minutes, maximum deatli time 

 2 hours and 10 minutes. The M. latipinna 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. Its minimum 

 death time was about 2)^ hours, the maximum was 

 32 hours. The sensitivity of F. simiHs is possibly 

 comparable to that of C. variegatus. Two F. 

 similis died in 7)^ and 10 to 19 hours. 



A chromogenic bacterium, Flavobacterium pis- 

 cicida, has been suggested as a possible cause of 

 the mass fish kills and associated sea-water dis- 

 colorations occurring along the west coast of 

 Florida (Bein 1954). Bein found that this bac- 

 terium was toxic to several species of fish although 

 he did not indicate the bacterial concentrations 

 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 

 bacterium" that we isolated from G. breds-in- 

 fested 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 

 Fundulus similis. The "red bacterium" has not 



