P.S.: Only those who do nothing never make mistakes!
P.P.S.: I managed to beat it on the first try. I have 10 fish left. This is considering that I positioned my units very poorly, and in the first round, the Psionic and Earth units were destroyed :D. If I position them properly, I can minimize losses even further. By the way, I used Fiura in the save file to simplify the task.