SUMMARY: An investigation of the bacterial flora of the representative flatfish, skate and lemon sole, was carried out by direct counts of special groups of bacteria and by the analysis of over 1700 strains of bacteria isolated from the fish. Luminous and agar-digesting bacteria occurred seasonally on fish. Luminous strains occurred mainly in the gut contents. A group of sea-water-loving Pseudomonas spp. which seem to require sea water for growth on initial isolation was present on the flatfish in variable numbers throughout the year. A more or less distinct intestinal flora was present in North Sea flatfish in which a homogeneous poup of micro-organisms provisionally labelled Gut Group vibrios predominates ; this group includes luminous bacteria. The bacterial populations of skin and gills were similar in both the fish studied and were composed principally of Gram-negative rods of the Pseudomonas and Achromobacter genera. The composition of the bacterial flora of the two flatfish, as calculated from an analysis of strains isolated from sea-water agar plates, was:Lemon sole : Pseudomonas 60 %, Achromobacter 14 %, Alcaligenes 8 %, Flavobacterium 5 %, corynebacteria 1 %, cocci 1 %, Gut Group vibrios 9 %, miscellaneous 2 %. Skate : Pseudomonas 53 %, Achromobacter 13 %, Alcaligenes 6 %, Flavobacterium 9 %, corynebacteria 2 %, cocci 3 %, Gut Group vibrios 12 %, miscellaneous 2 %.
Paralytic shellfish toxin concentrations were measured and individual toxin profiles were monitored in axenic batch cultures of Protogonyaulax tamarensis and Protogonyaulax catenella. High pressure liquid chromatographic methods were used that allowed the separation of all 12 known paralytic shellfish poisons, including toxins Cl, C2, and C3, from a single sample. In isolates of both Protogonyaulax species, total toxin levels were relatively low after inoculation, increased rapidly in early to midexponential growth to a value 100 to 300% of that at the initial time point, then decreased by 86 to 95% as the culture aged. Although the concentrations of individual toxins per cell followed the same general pattern as that seen for total moles of toxin per cell, variability in toxin profile with culture age was observed. In P. tamarensis, the mole percent of neosaxitoxin increased substantially from 8 to 44% as total toxin levels per cell decreased. A concomitant decrease in the mole percent of saxitoxin with culture age was noted. Although not as precipitous, changes in the mole percent of specific toxins from P. catenella were also observed. The mole percent of gonyautoxins I and IV increased, while that of gonyautoxins II and III decreased. These data suggest that the toxin profile in isolates of Protogonyaulax can change, sometimes significantly, with changing environmental variables. Protogonyaulax species produce an array ofchemically similar neurotoxins that differ in their biological toxicity (8,17).
Samples of sediment, water, and fauna were tested for the presence of Vibrio parahaemolyticus and the related biotype V. alginolyticus. Altogether, 379 samples were analyzed quantitatively by using a starch-agar medium. Invertebrate and sediment samples were invariably positive for V. parahaemolyticus, whereas water samples were quite variable. Samples of the Pacific oyster (Crassostrea gigas), obtained on a regular basis for 26 months from a single environment, showed a close correlation between total numbers of mesophilic vibrios and the overlying water temperature; the seasonal counts of oysters ranged from less than 10 to greater than 100,000 per g. Ecological implications and possible pathogenicity of these vibrios are discussed.
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