We are following the protocol of mammalian tissue and Mouse/Rat to extract DNA from fish (page 28, 23 and 24): https://assets.thermofisher.com/TFS-Assets/LSG/manuals/purelink_genomic_man.pdf, but no DNA is getting extracted. We've already tried to cut the tissue into smaller pieces, add Tris-EDTA buffer to remove the etanol 95% from the tissue before adding PureLink® Genomic Digestion Buffer and Proteinase K, and perform a second elution step, but nothing works. What could be happening?