From my understanding, Seaman was developed by Vivarium and the English work was done by Jellyvision (the You Don't Know Jack guys). SEBA published it. No clue if Seaman is owned by SEGA like Bayonetta or if it's more of a Iron Man sort of thing where SEGA just published and Seaman is Vivarium owned.
Seemed in the Dreamcast days, SEGA treated the fish man like a first party character.