Did you feed a dolphin before ?

Did you feed a dolphin before ?
Have you fed a dolphin before
Both are correct.
But, usually, we don't feed a dolphin everyday, so we should say: Did you ever feed a dolphin before?
Same reason in reverse; you can't say: did you ever have your dinner?

Did you feed a dolphin before ?-(Past tenst)
是解你有沒有餵過海豚之前。
Have you fed a dolphin before ?-(Present perfect tenst)
是解你有沒有餵過海豚之前。
(一樣)
Right!

這兩句分別是什麼意思?

意思一樣,問題都指出 "你有否餵過海豚?"

沒有文法錯誤