BUCK: BACTERIOLOGY OF ELASMOBRANCH FISH 



technique (Yap 1979), although this technique has 

 inherent weaknesses (Horsley 1977), especially in 

 examining shark skin, because it is abrasive and 

 essentially three-dimensional. Nonetheless, 

 counts obtained by swabbing a known area were 

 always higher than those achieved by pressing a 

 membrane filter on the skin, probably because the 

 membrane did not recover bacteria associated 

 with the lower portion of the denticles. The fibrous 

 texture of the swab, while prone to some shredding 

 unless care was used, may have allowed penetra- 

 tion into the skin. Perhaps an agar-coated slide or 

 "paddle" which could be pressed onto shark skin 

 would be more effective, although such a proce- 

 dure might be unwieldy in the field. 



Table 1 shows the number of bacteria recovered 

 from the skin of various elasmobranch and os- 

 teichthyan fish. Elasmobranch skin showed a very 

 wide range of counts both among genera and 

 within a given species. Data in Table 1 indicated 

 that there was no obvious correlation between 



TABLE 1 . — Number of bacteria on fish skin ( Bacto-marine agar i 



'Tank held 



bacterial counts on tank-held and freshly caught 

 elasmobranchs, although bacterial counts on skin 

 of three tank-held Atlantic sharpnose sharks were 

 about two orders of magnitude lower than counts 

 for one specimen of the same species caught in a 

 gill net. Three of the highest counts on shark skin 

 noted in Table 1 (bonnethead, 410,0007cm 2 ; 

 blacktip, 530,000/cm 2 ; blacknose, 330,000/cm 2 ) 

 were from fish which had been dead for 3 h. This 

 suggests that bacteria rapidly colonize skin of 

 dead sharks. Yap (1979) reported varying counts 

 on skin of freshly caught shark which depended on 

 the area of the fish sampled. His counts (310- 

 1,900/cm 2 ) were, in general, lower than those re- 

 ported herein, and were estimated from broth di- 

 lutions and not plates. The shark skin sampled 

 here displayed relatively high bacterial counts 

 which are of considerable significance if the 

 sharks are to be used for food. Large numbers of 

 bacteria could be deposited onto flesh which sub- 

 sequently may undergo more rapid spoilage if not 

 adequately washed and/or refrigerated. With the 

 exception of the bighead searobin, Prionotus 

 tribulus, the counts on osteichthyan fish were 

 quite similar and within the range reported in 

 other studies (Horsley 1977). 



Qualitative Analysis 



Table 2 shows the number of isolates and genera 

 of bacteria recovered from elasmobranch and os- 

 teichthyan fish and from waters where the fish 

 were taken or held. The Gram negative bacteria, 

 especially Pseudomonas, Vibrio, and Cytophaga, 

 accounted for 89% of the 111 isolates from skin. In 

 other studies, pigmented Gram positive isolates of 

 Micrococcus, Bacillus, and Corynebacterium were 

 the most common (30 strains) on the skin of one 

 shark (Carcharhinus sp.) caught off India; only 5 

 cultures of Gram negative Achromobacter, 

 Flavobacterium, and Vibrio were recovered (Ven- 

 kataraman and Sreenivasan 1955). Pseudomonas 

 (40% ), Micrococcaceae (309c ), and Moraxella (15% ) 

 were dominant on skin of a freshly caught shark 

 off Australia (Yap 1979). The data here for skin 

 (Table 2) show a similar percentage for 

 Pseudomonas but considerably fewer isolates of 

 Moraxella and Gram positive cocci. 



Table 2 shows that for Gulf of Mexico sharks, 

 fewer genera were recovered from intestines than 

 from other areas, but that the Gram negative gen- 

 era were predominant and species of Photobac- 

 terium, Pseudomonas, and Vibrio accounted for 

 57% of the isolates. Gram positive bacteria (one 



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