3' is the usual size but 4' is not uncommon... even in captivity in private hands A arapaimag reported 1-2 of his to reach 4'They are beautiful! How big do they get? They look a LOT like Armored Catfish (that's all I know the species as - I have one, very hard to get a pic of, as he's always in hiding, like my Spotted Raphael), but with a different head!
They are all from the same family Doradidae aka thorny catfish or armored catfish, although there are other catfish called armored catfish - corydoras, hoplos, and Co - Callichthyidae https://www.planetcatfish.com/common/family.php?family_id=1
It's most usually nearly impossible to go by descriptions to ID a species. You'd need to provide a few good photos to be sure. I'd either catch the fish in the net and bring it to the front glass to photograph or place it in a phototank, makeshift or not.I have not been able to find any pics online of my species - think of a Spotted Raphael, but without the spots - about 8" max, same size as a Spotted (I've had him for ~10yrs now), but not a Acanthodoras spinosissimus
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In fact, I just went through the whole page on Planet Catfish and nothing aside from the Spotted looks even remotely like it -
https://www.planetcatfish.com/common/subfamily.php?subfamily_id=8
Though he does kind of look like a Platydoras Costatus - not sure the head is that flat though -
https://www.planetcatfish.com/common/species.php?species_id=166
10 years is a very respectful term! God job. I'm guessing it's a raphael. Costatus is a very common species. These guys lived 20-30 years in some people's hands and are still alive today.
I didn't get your "Nautilus" comment the first time as I thought of the animal but now I guess you meant Captain Nemo's armored submarine of Jules Verne. Silly me.
This thread is not a fitting place for discussing Doradiids. I am suggesting for us to continue, if we do, in my niger thread I linked or for you to make your own ID thread for your catfish.
We may have to ask a mod to transfer relevant posts of yours and mine to my niger thread.