well i got my 2 tomatos together they chase each other around and i heard some wher that the temp has to be warm to have a succesful breed (or 4 them to start laying eggs and stuff)
the female is the one doing the chasiing most likely....do you have a anemone? my two stopped chasing eachother after i bought a LTA.....Also, the chasing can be a form of 'courting' or flirting...