Learn Croatian: Koji mamac je najbolji za ovu ribu? - Which bait is the best for this fish?

Enclitics generally take the second position in a sentence. This can mean either after the first single word or after the first complete phrase. Since Koji mamac (Which bait) is a single logical unit, placing je after the whole phrase is very common and natural.

Could I use Kakav mamac instead of Koji mamac?

Yes, but the meaning shifts. Koji means "which" and asks you to select from a specific set of options (like choosing between worms or a spinner). Kakav means "what kind of" and asks for a description of the bait's qualities.

Why is the adjective najbolji in its definite form here?

In Croatian, all comparative and superlative adjectives are exclusively definite. There is no indefinite form for a word like najbolji (the best), so it always takes the definite ending, which is -i for masculine nominative.

Why do we use the accusative case ovu ribu after the preposition za?

When the preposition za is used to mean "for" in the sense of purpose, benefit, or intention (like bait intended for a fish), it requires the accusative case. This is why ova riba changes to ovu ribu.