I am working on developmental toxicity in zebrafish embryos. I have optimized and completed treatment for various toxicity assays. Now I am not able to maintain embryos till the required time (3 hpf to 7 dpf exposure). The embryo coagulates as we place them for treatment (this happens even in the control group). If at all the embryo hatches (48-72 hpf), it cannot survive past 4-5 dpf. I tried checking and replacing all the treatment media including, E3 media, distilled water, my drug, etc. Still, there is no change. Kindly suggest a way to overcome this.