Ontogeny

One unique feature of the Vandellia is that, while the adult
exhibits this hematophagic behavior, the young Vandellia are born with
a comparative mouth structure, compared to its nonparasitic cousins.
During the Vandellia's development, its mouth structure somehow
changes into that of the parasitic parent, and the behavior shifts
from consumption of other fish's mucus, scales, and small
invertebrates to hematophagy. Unfortunately, the juveniles were only
recently found to have this structure, and it is yet unknown how the
mouth shifts to accomodate its hematophagic lifestyle.