The fins underneath the belly are called "ventral fins"... The ones on the sides of the head are the "pectoral fins".
An easy way to remember is kind of a weird train of thought I use... When I see pectoral, I think "pecs" which makes me think "torso" which also makes me think "arms"... The pectoral fins look like little betta hands. lol it's strange I know, but it works! Trust me!