Boy, I tell you, I have had the WORST luck lately! I have a small batch of
rainbowfish fry (neon dwarf, M. praecox) almost two months old.
I just noticed that the three smallest fry have a SLIGHT problem: each has a
white, fleshy-looking nodule protruding vertically from the tops of their
heads. It's quite large (proportionately) about the same size (or larger)
than their eyes.
It looks like the margins of the nodule (where it emerges from their heads)
may be slightly rimmed with black - although that could just be the upturned
edge of the scales catching the light. The fry are about 1CM long - the
nodule is about 1MM.
Whaddaya think - freakish birth defect, or some kind of... head parasite?
(It's all very "From Beyond"!)