Q. Why are we permitted to eat fish, after all Noach never saved the fish?

A. Let me first explain your question. After the end of the Mabul described in detail in this parsha, the surviving humans were given the right to consume animal meat, as the posuk says; “Every moving thing that lives shall be yours to eat; like the green vegetation, I have given you everything” (9:3.) Rashi explains quoting from Sanhedrin 59b; For I did not permit the first man [Adam] to eat meat, but only vegetation, but for you, just as the green vegetation which I permitted for the first man, I have given you everything. Ramban explains the reason being that Noach saved all animals from destruction, so therefore acquired the right to consume them. The question begs itself, since the fish were not included in the decree of destruction by the Mabul as Rashi (7: 21) quotes from the Talmud, (Sanhedrin 108a) Noach did not need save the fish. Why are we then allowed to eat fish?
A number of different answers have been offered. Avnei Nezer maintains that indeed the fish did not become permitted at the time of Noach, they only became allowed at the time the Torah was given and it specifically instructed us as to what fish we can consume. Therefore, he explains, Avraham Avinu did not serve fish to his heavenly guests in Parshas Vayero, since it was not kosher yet. In his name, Pardes Yosef also explains why we eat fish on Shabbos, since by consensus all sages agree that the Torah was given on that holy day. (Shabbos 86b)
However, Rav Yaakov Kamenetzky Zt”l in Emes LeYaakov opines the opposite. Fish because of their lack of prohibitory mitzvos were always permitted, as you perceptively noted. (See Chulin 27b) Meor Veshemesh in this parsha further explains that when Adam repented and made teshuva, he was able to fix and bring a “tikun” to all of creation. However the tikun was not total and the land animals remained affected. They still required the further tikun provided in the Teiva. That tikun was obtained by the tremendous effort and exertion of Noach and his children in feeding and serving the animals in the Ark during the year of the Mabul.
There are also different opinions in Midrashim and Talmud as to why the fish didn’t die, even though the floodwaters were boiling hot, such as the floodwaters were hot only above the ground and not above the oceans. (Bereishit Rabbah 32:11). The waters around the teiva were cold and therefore Noach did save the fish.
There is also a most unusual opinion that the teiva contained an aquarium.

Rabbi A. Bartfeld