Originally posted by Cangrejo:

I got 1 raw fish from level 1 perch, 1 from level 1 tuna and 4 from level 2 tuna. And the bait doesn't seem to change the chances but idk for sure

Thanks, that was very insightful. I did as I said and only turned the Q1 perch into bait and turned the others into fish:
Pike Q3 --> 7 raw fish
Perch Q2 --> 4 raw fish
Tuna Q1 --> 1 raw fish

So it seems meadow fish give the same amount of raw fish independent of species, but depending on quality.