  We propose to employ emission line luminosities obtained via optical
spectroscopy to estimate the content of neutral hydrogen (HI) in galaxies. We
use the optical spectroscopy data from the Mapping of Nearby Galaxies at APO
(MaNGA) survey released in the frames of public DR17 of the Sloan Digital Sky
Survey (SDSS). We compare the HI mass estimated by us for a large sample of
SDSS/MaNGA galaxies with direct HI measurements from the ALFALFA survey and
find a tight correlation between the masses with the correlation coefficient
(CC) of 0.91 and the r.m.s scatter of 0.15 dex for the logarithmic mass. The
obtained relationship is verified via another sample of MaNGA galaxies with HI
masses measured with the Green Bank Telescope. Despite the coarser angular
resolution of the radio data, the relation between the estimated and measured
directly HI mass is tight as well - in this case CC=0.74 and the r.nm.s. is
0.29 dex. The established relations allow us to estimate the total mass of
neutral hydrogen as well as the spatial distribution of HI surface density in
galaxies from optical spectroscopic observations only in a simple and efficient
way.
