Fish options

salmon would be a good choice! you could just bake a filet (or air fry), and mix the flaked fish into something like mashed potatoes (:

You want to do shellfish as well. As far as the fish id start with salmon. White fish and fatty fish like cod, catfish, mackerel and sardines is good for them. As far as shellfish crab and shrimp. All can be made well with like pasta or what I did was cut it really small and mixed with sauce like Alfredo or butter sauce

Look at the solid starts app for serving options.
Be mindful that fish and shellfish allergies can appear hours after eating in forms of vomiting and diarrhea. Reactions also may not appear every time they are consumed.

I did salmon with my baby and she loves it! She's also had tuna and cod, haven't tried shellfish yet

My toddler loves sardines. Just have to watch the salt content, I get it without bones. Serve it whole right outside of the can.
You can also look at solid starts and it can give you advice on how and when to serve foods to babies.

Thanks everyone, really helpful! Will try give these a go!