Toxicological biotest on Diptera larvae to detect ciguatoxins and various other toxic substances

A toxicological test was developed using a new animal sensitive to various toxins, especially ciguatoxin (CTX), which poisons humans who eat tropical fishes. The larvae of Parasarcophaga argyrostoma (Diptera, Sarcophagidae) were selected for their marked ability to consume spontaneously large quantities of various proteins; meat, fish flesh or liver, mussels, etc. Larvae grown on meat overnight can easily be observed without requiring optical instruments. Ten larvae were placed on 5 g of the sample to be tested, and left for 3-24 hr. Samples containing > 1 ng of CTX/g of flesh (moray.eel CTX) killed the larvae in about 3 hr; samples with lower concentrations inhibited larval growth, which can be noted with the marked eye. These readings were rendered objective by weighing the larvae before and after their being placed on the test sample and comparing the result to that of the control. The reading with the naked eye seems to be satisfactory up to 0.2 ng of CTX/g, while that by weighing was acceptable up to 0.10-0.15 ng/g. The coefficient of variation in the sensitive zone (approximately 50% of normal growth) was about 25% for a series of 11 experiments. P. argyrostoma larvae are sensitive to various other toxic substances, such as tetrodotoxin, okadaic acid, aflatoxin B1 and amanitin. The test is extremely simple in its theory and practice. It does not require complex materials or equipment and it is very inexpensive. It could be used to detect ciguatera toxins in the monitoring of fishing areas and for the commercialization of big-sized fish.