I have a knife made especially for cutting frozen food ,it has fine teeth similar to a hacksaw or bandsaw ,if you have a knife that is similar it will work

Agree. Use a serrated-edge blade knife. The deeper the serrated edge the easier. If you don't have one a crosscut saw will do it. You can always clean it well first with hot soapy water and alcohol. Butchers often use a band saw.

Dave

I don't think you need a really hefty knife/saw for fillets. But a serrated knife would be easier - if you have a bread knife, or even a clean drywall saw. I wouldn't use a steak knife though - I think something with a longer blade would work better.

Maybe an electric knife?