There's a singular-VS-plural-problem here: "Tibi placet piscis salsus?" (or possibly the construction with the enclitic "-ne", as it appears here) would mean "Do you like THE -" or "- A salty fish". The general "salty fish" (surely plural, right?) would be plural "pisces", just like in English: "Tibi placent pisces salsi". ... or are we supposed to read some kind of generic singular into this?
The proffered "correct answer" is Do you like salty fish? I'd say that this is inadequate, inasmuch as it suggests that the questioner is in genuine doubt about the answer (s)he will receive. Every account I've ever read about the meaning of the Latin suffix -ne maintains that it exhibits the clear expectation, on the part of the questioner, that the answer will be positive. Therefore: "You like salty fish, don't you?" (with high tone on like and low tone on don't).