How can dead fish alive?

I read surah Al_Kahf verse 61 > But when they reached the junction of two seas they forgot their fish. and it took its way through the sea as in a tunnel. when I reached this above verse I analyze it as a portal where the fish alive and made a tunnel in sea for Prophet Musa. Like other miracle is it also a miracle if yes then can anyone replied me through the reference? and in which tafseer it has been discussed scientifically. I read it in tafseer ibn kathir.