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The effect of sodium chloride concentration (3, 4, 5, 6, 8, 10 and 12%) and storage temperatures (4°C, 10°C, 15°C and 30°C) on toxin production by Clostridium, botulinum isolated from tropical fish was studied in anaerobic cooked meat medium. The combined effect of sodium chloride (3, 5%), low pH (5.5) and low temperature (15°C) on toxin production by C. botulinum was also examined. The toxicity was tested by mouse bioassay. An increase in lag phase was noticed by increasing the salt concentration. At 30°C, spores of C. botulinum type E were able to grow and produce toxin up to 3% salt (aw = 0.976), whereas for types C and D the limiting salt concentration was 4-5% (aw = 0.97-0.974) and for types A and B it was 8% (aw = 0.952). By lowering the storage temperature, an increase in lag phase and time to toxicity was noticed for type Eat 3% salt and for types A, C and D at 5% salt level. The probability of growth and toxin production at 5% salt decreased as the pH and storage temperature (combined stress) was decreased. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine the microbiological quality of farmed giant freshwater prawn (Macrobrachium rosenbergii) collected from four freshwater farms located in Kerala (India). Microbiological counts on whole, deheaded, and deheaded and deveined prawn as well as on head and intestine were determined. Average counts (log10 cfu g-¹) on whole prawn were 6.9 (total mesophilic counts (TPC) at 37°C) and 4.1 (psychrotrophic count at 7°C). The results indicated that the aerobic counts were within the acceptable limit. The levels of enterococci and faecal coliforms in farmed M. rosenbergii were high. There was an increase in the numbers of enterococci and Staphylo- coccus aureus after deheading. The major groups of bacteria comprising the flora of M. rosenbergii were Aeromonadaceae, Enterobacteriaceae and Pseudo,nonas. Farmed M. rosenbergii carried pathogenic bacteria such as Enterococcus spp., S. aureus, Aeromonas hydrophila, A. veronii biovar sobria and Clostridium perfringens. The results of the study sug- gest adoption of good farming and post harvest practices to improve the microbiological quality of farmed freshwater prawn. [Article copies available [ABSTRACT FROM AUTHOR]