As advised by Silurus on PCF, yes, they are Ictalurus punctatus http://www.planetcatfish.com/common/species.php?species_id=6
You've learned a lot with these fish and you deserve many praises for your dedication and honesty and openness.
I agree with Wednesday13 for sure. They can live 20 years and easily more. Your 250 L tank is not enough if you aim for their best. 100 gal tank is not either, not even close. Think more of at least 1000 gal (US or UK ). If you can't give them that, I am afraid you have to find a different proper home for them. UK climate is close to their native range, so an outdoor pond would appear much more likely to find than a large enough tank. Just make sure to follow the local laws. I imagine, since this fish is an exotic to UK, it should be confined in a lawful way in any outdoor pond (if permitted to be placed outdoors at all). Indoor pond is ideal.
You've learned a lot with these fish and you deserve many praises for your dedication and honesty and openness.
I agree with Wednesday13 for sure. They can live 20 years and easily more. Your 250 L tank is not enough if you aim for their best. 100 gal tank is not either, not even close. Think more of at least 1000 gal (US or UK ). If you can't give them that, I am afraid you have to find a different proper home for them. UK climate is close to their native range, so an outdoor pond would appear much more likely to find than a large enough tank. Just make sure to follow the local laws. I imagine, since this fish is an exotic to UK, it should be confined in a lawful way in any outdoor pond (if permitted to be placed outdoors at all). Indoor pond is ideal.