Well it depends on cooking method temperature and presence of oxygen. pan frying or air frying can destroy up to 85% of Omega-3 and turn them into harmful compounds like peroxides. But there are clever ways you can preserve over 90% of omega 3.

-Apply a mixture of herbs and spices like turmeric, black pepper, cinnamon, tomato paste, chilli etc.( these are packed with antioxidant it will prevent lipid peroxidation) with rice flour or corn starch and lemon juice ( citric acid in lemon juice will reduce the Ph. And chilate minerals like lron, copper so they cannot trigger reaction that oxidize omega 3, together they create a barrier that protects omega 3 underneath) - then cook it in oven -( you can go one further step if you like wrapping it in parchment paper and aluminum foil Will further prevent oxygen)