So right now only WK claims that
うみざかなis a “very common reading” which starts to be verdy dubious
I can’t tell you if it’s very common or not, because I am not good enough at Japanese, but I found some websites which give the reading うみざかな:
https://ja.hinative.com/questions/4254137
And this HiNative post, where a Native Speaker (i think) replied “両方とも同じ意味ですが、私は最初の言葉を聞いたことがありません。” (最初の言葉 referring to かいぎょ)
So at the very least it exists, I guess.