Background: The use of fish embryos for toxicity testing (FET) is under consideration as an alternative to traditional acute fish toxicity tests. For the past two years, a marine fish embryo test (mFET) has been under development in our laboratory as a routine ecotoxicological test for risk assessment of potential contaminants around the Qatari coastal area. Objective: The objectives of this study were to: a) develop and use a flow-through system to optimize the mFET test conditions to maintain stable concentration of volatile compounds; b) correlate the flow-through mFET to the conventional acute fish test; c) investigate changes in sensitivity of Arabian Killifish embryos to toxicity of chlorine-produced oxidants under flow-through conditions compared to the previous static mFET. Methods: The flow-through system was carried out using custom designed glass chambers. Peristaltic pumps were used to ensure constant flow conditions. To investigate the effect of the flow-through mFET on toxicity of chlorine, fertilized eggs were exposed to aqueous concentrations of calcium hypochlorite for up to 240 hours. The investigated endpoints included; coagulated eggs, somite development, heartbeat, tail detachment, hatchability and post-hatch mortality. Results: The present investigation demonstrated that the custom designed flow-through system enhanced the FET conditions compared to the static FET. The flow-through system stabilized chlorine concentration and provided a larger volume which allowed an increase in the number of test embryos and sufficient test media for chemical analysis. Conclusions: Our data showed that the flow-through system improved the mFET assay for conditions like control survivability and for the main goal of bringing the sensitivity of the embryos into alignment with published data on the effects of chlorine-produced oxidants. This dataset, in conjunction with our previous work on static test conditions provides a wider range of applicability for the assay. In order to further support the mFET as an alternative to acute fish testing, the flow-through FET is currently being extended to other potential compounds of interest.


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