Yes, any type of unsmoked fresh raw fish is fine, raw scallops, raw clams, raw shellfish of almost any kind - just remove bones or shells and cut into strips if needed. Prawns, crayfish etc should be deshelled and cut up. Raw squid can be used too.
But in all honesty unless they are just offcuts from your regular food I wouldn't but any in just for your axies, it could get expensive. If you want an interesting snack for your axies try live shrimp - fun to chase and eat for the axies, great to watch axies on the hunt for you.
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