I wrote "The fish ON the table is good" and it was accepted, but the suggested solution is "The fish FROM the table is good." In the statement "Peștele de pe masă este bun", is it clear whether the fish is actually on the table right now, or can it mean both that the fish is on the table and that it has already been lifted from the table?
It is correct.
However, when preceded by a preposition and in lack of a pronoun or adjective, the noun in Romanian takes the indefinite form, although you would use the definite article in English.
The fish from the table is good. - Peștele de pe masă e bun.
The fish from my table is good. - Peștele de pe masa mea e bun.
The fish from the black table is good. - Peștele de pe masa neagră e bun.