In most places outside Japan sea eel is frozen and often re-heated in a toaster. In the USA all fish is frozen to kill any bacterial microbes and it’s by law and without fail that it must be!
Japanese Anago (sea eel) at least where I eat, is never frozen and only caught domestically and is 100% fresh. It is served two ways, either with a sweet sauce named amadare, or known as tsume, or naturally without any sauce. I use some sea salt on my natural anago to liven it.