From saltwater fish under 400gr i think. If i am wrong for the size please someone to correct me.

There are many ways to make them from mackerel and herring either straight from fish or use table on the captains boat to convert your fish flaps and other bait from fish from above to the fish pieces.

I fond that sometimes, it's beneficial to just purchase the bait as opposed to making it yourself.
It all depends on the time versus the revenue.