Loop mediated amplification question

  Hi, I'm Giana Gomes, I'm new in this group. I work as a researcher worker for the Aquaculture Department from James Cook University-Australia.
 
I'm starting a project with the Lamp technique. I need to differentiate 2 species of fish using this technique. My question is, how many (minimum) base pairs do I need in the 4 (F3/B3 FIB/BIP) sets of primers to differentiate the 2 species? Is it enough to have just 1 or 2 different base pairs in just 1 or 2 of the 4 sets of primers to give me the specificity for each specie?
 
Thank you.