definite and/indefinite articles required here: for example, The shark eats the dolphin, or a shark eats a dolphin, and so on.
It depends on the context.
The Indonesian sentence sounds like a sort of a statement.
If that is the case and you're stating something in general, then it would be:
"Sharks eat dolphins"
BTW, do sharks really eat dolphins ?
The Indonesian sentence uses the singular form.
"lumba-lumba" looks like a reduplicated form, but it isn't.
It's the singular form.
There is no plural form for this animal.
It's the same with some other animals : "kupu-kupu" (butterfly), "kura-kura" (turtle).
The plural form (reduplication) is not used when stating something in general.
"Dogs like bones." ==> "Anjing suka tulang."
The following sentences are grammatically incorrect:
"Anjing-anjing suka tulang."
"Anjing suka tulang-tulang."
"Anjing-anjing suka tulang-tulang."
You will be understood of course, but it's grammaticaly incorrect.