  In the disks of four jellyfish galaxies from the GASP sample at redshift
$\sim 0.05$ we detect molecular gas masses systematically higher than in field
galaxies. These galaxies are being stripped of their gas by ram pressure from
the intra cluster medium and are, in general, forming stars at high rate with
respect to non-stripped galaxies of similar stellar masses. We find that,
unless giant molecular clouds in the disk are unbound by ram pressure leading
to exceptionally high CO--to--$\rm H_2$ conversion factors, these galaxies have
a molecular gas content 4-5 times higher than normal galaxies of similar
masses, and molecular gas depletion times ranging from $\sim$1 to 9 Gyr,
corresponding to generally very low star formation efficiencies. The molecular
gas mass within the disk is a factor between 4 and $\sim$100 times higher than
the neutral gas mass, as opposed to the disks of normal spirals that contain
similar amounts of molecular and neutral gas. Intriguingly, the molecular plus
neutral total amount of gas is similar to that in normal spiral galaxies of
similar stellar mass. These results strongly suggest that ram pressure in disks
of galaxies during the jellyfish phase leads to a very efficient conversion of
HI into $\rm H_2$.
