There's not really enough info to determine what's going on.
Is it laying on its side? That would worry me. If it's sitting on the bottom on its belly then I guess that could be part of spawning behavior, but it could also be caused by other illness or stress.
Spawning behavior I'd recognize if I saw it myself but I can't tell from your description.
Approximately how big are the fish and what size tank are they in? How often are water changes done? What are the water parameters? (Nitrites, Nitrates, Ammonia, pH - that should be the first thing you check if you think there's a problem)
Any other information you know about the fish and the aquarium would be great too.