Sorry but the swordsmith’s correct name may be “兼道” but this sword, like many others, is purposefully signed “魚道”. It is not an accident that it looks as much like “fish” as possible. Much more like “fish” than anything else, so we can deduce that its 100% intentional. Which makes me wonder why we refer to the signature as “兼道” when in fact it is signed to look like “魚道”, intentionally.
I guess it is a stylistic choice but I wonder why we don’t just call it what it is. Kanemitsu (a lot of them) did it too.