Ibn Ezra (2): Even though he prayed "mi'Me'ei ha'Dagah" (2; while in the fish), it is in past tense. A Navi's Tefilah or Brachah is with Ru'ach Nevu'ah. It was already decreed, so past tense is used, e.g. "Lakachti mi'Yad ha'Emori", "va'Yet Shichmo Lisbol" (Bereishis 48:22, 49:15).

Malbim: His Tefilah is divided into three parts. (a) When they cast him to the sea, he despaired from life. When the fish swallowed him and he remained alive in its innards, he saw that miracles are done for him so he will live. (b) After the fish cast him out, he was cast again onto a great depth of water and despaired again. When the female fish swallowed him, he saw that he will live. (c) When he was cramped in the female fish, he accepted to heed Hashem's voice and go to Ninveh like He commanded. "Karasi? va'Ya'aneni" applies to the two times that he was cast to the sea; he called to Hashem, and was swallowed each time. Now, in the stomach of the fish, "Shivati", and I trust that "You will hear my voice" and take me out to relief.

Rashi: He was in the stomach of the fish, which is like the grave for him.

Radak: Since he was still alive ¹ , he knew that he will come out alive.