- Lack of natural COVID-19 infectivity- Insufficient affinity of zebrafish Ace2 and SARS-CoV-2 S protein- Lack of lung- Growing temperature (28 vs. 37 °C)- Probably need of transgenic expression of hACE2 or viral adaptation is required- Non physiological conditions of the SARS-CoV-2 infection. The gene discussed is PROS1; the disease is COVID-19.