Daphnia magna as a bioassay system for histamine in tuna extracts

Live Daphnia were subjected to varying concentrations of aqueous extracts from three lots of commercially canned tuna. Two of the lots had been identified as causing “scombroid poisoning”, and contained high histamine (Hm) levels. The third was a control lot of store-bought tuna. The extract of the control fish was used either alone or with the addition of Hm at levels equalling or exceeding the Hm concentrations in the other two lots. Twenty Daphnia per group were exposed for 60 minutes: responses (loss of activity or infrequent twitching) were recorded at ten minute intervals. The response increased with time, and was dependent upon the concentration of Hm presentregardless of source. LD50's for the various time and concentration gradients are shown. The method might be useful in quality control testing.