one goldie being picked on

i have one goldfish ("smokey") that the other two ("snoopy" and "koda") will
occasionally nuzzle/chase/follow/harass. most of the time, they all get
along fine and usually just ignore each other. but, every once in awhile,
they start this weird behavior. at the same time, smokey is also acting
strangely...like suspending herself facing down...or, hiding in a cave. what
is going on? is it possible that smokey is female and snoopy and koda are
males and it is "that time of year"?