Evolution of methods for assessing ciguatera toxins in fish.

Ciguatera toxins are odorless, tasteless, and generally undetectable by any simple chemical test; therefore, bioassays have traditionally been used to monitor suspect fish. Many native tests for toxicity in fish have been examined, including the discoloration of silver coins or copper wire or the repulsion of flies and ants, but all of these were rejected as invalid. Oral feeding of fish to cats or mongoose is a simple and relatively sensitive assay, but cats often regurgitate part of the meal. Feeding tests described above have been used in screening fish for toxicity, but they are cumbersome and nonquantitative. A mouse bioassay was developed; unfortunately, this procedure requires purification fish extracts, since mice are not very sensitive to ciguatoxin. An alternative to the use of mice is the mosquito bioassay, which was recently used to obtain a dose-response relationship between ingested ciguatoxin and clinical symptoms in man. This assay correlates reasonably well with cat and mouse bioassay. Many other bioassays have been developed using chicken, brine shrimp, and the guinea pig atrium. All traditional bioassays have one common disadvantage, the lack of specificity for individual toxins. Recent studies have also focused on the development of chemical methods, i.e., TLC and HPLC, for the detection and quantification of ciguatera-related toxins (okadaic acid and ciguatoxin and its analogs). Alternative assays based on immunochemical technology have been developed and show the greatest promise for use in seafood safety monitoring programs. For earlier methods (RIA and ELISA formats), liver extracts from ciguatoxic eels were used to prepare ciguatoxin antisera. The assay has been further adapted to a solid-phase immunobead assay (S-PIA), which has a very high potential for use as a marketplace screening tool to separate ciguateric fish. This assay can also be used to monitor reefs for ciguatera potential. Historically, attempts to validate methods used to measure ciguatera toxicity have been plagued with a lack of specificity and reference standards. These restrictions have been resolved, and a study is under way to evaluate the precision and accuracy of a low-cost, simplified field and laboratory S-PIA kit (Ciguatect, Hawaii Chemtect International, Pasadena, California, 91109), through an international interlaboratory trial using the AOAC/IUPAC validation mechanism.