oa Extending the application of Arabian Gulf killifish embryo test for risk assessment of heavy metals in Qatari waters

Fish embryos are excellent models for studies aimed at the understanding of toxic mechanisms and the indication of possible acute and chronic effects. For the past 3 years, an Arabian killifish fish embryo test (FET) has been developed in our laboratory as a routine ecotoxicological test for risk assessment of potential contaminants in the Arabian Gulf around Qatar. To further explore the applicability of the killifish embryos as a model for the Arabian Gulf conditions, we tested the toxicity of heavy metals such as zinc and copper using Arabian seawater conditions. A breeding stock of sexually mature killifish, variable in age, was used for egg production. Eggs from several females were pooled and placed in salt water for fertilization. Embryos were examined under a dissecting microscope and viable embryos that were less than 6 h were selected. Eggs were distributed in replicates by stratified random assortment into 24 well plates. Observation was performed in 48-hour increments (± 2 hours). Endpoints included: coagulated eggs, absence of heartbeat, tail deformity and delayed hatching. Literature review was compiled for fish species that have been recommended for ELS toxicity testing. The data collected was then used for comparison to the current findings and the sensitivity was then extrapolated for the killifish embryos. Past findings indicate that toxicity is reduced in high salinity waters. This was confirmed in this study where at salinity 40 psu there were no apparent effects on embryos for any concentration tested and all embryos hatched at expected duration. When salinity was reduced from 40 to 20 psu, metal toxicity increased significantly (P > 0.05). Examination of the existing literature on acute Zn and Cu toxicity to fish and larvae showed similar results to the findings in this study using killifish embryos. The findings further support the use of killifish embryos as indicator organisms for environmental risk assessments of Qatari waters. Benefits include; sensitivity to wide range of substances and conditions, animal alternative, ease of fish breeding, clarity of the embryos, reduced sample size, reduced waste generation and shorter study duration. By expanding this test to evaluate its sensitivity towards other potential contaminants in the Arabian Gulf, we will further enhance the potential of killifish embryos to be adopted as a model species in marine ecotoxicology and risk assessment in this region.