The size of 5 mm. is doubtful to be a fish egg, maybe 0.5 mm.
Of course, larger fish lay larger eggs.
I have seen small tetras spawn and the eggs, although numerous, are extremely small.
I would estimate a cichlids eggs to be in the vicinity of 1 mm. or so, maybe less.
Other people with more interest in spawning fish might chip in with size estimates of fish eggs.
Bill in WI