  We present our analysis of a set of populations of massive black hole (MBH)
binaries generated in the recent semi-analytic model of galaxy evolution
(SHARK). We focus on studying gravitational wave (GW) emission produced during
MBH mergers in terms of their detectability with current and future detectors,
namely, Pulsar Timing Arrays (PTAs) and Laser Interferometer Space Antenna
(LISA). The key advantage of SHARK is that it provides a way to explore a
number of distinct models of MBH and galaxy evolution processes within a
consistent framework and it was also successfully tested against current
constraints from electromagnetic observations. In our work, we studied 12
models that vary in terms of their MBH seed formation scenarios and we tested
two different MBH growth and feedback models.
  Based on our estimates, we find that LISA will be able to detect several to
several tens of merger events per year for the most and least massive seed
scenarios, respectively. We also show that the strength of this relation
depends on the MBH growth model, where in the most extreme case, we find twice
as many detected events for the same initial seed masses. Finally, we estimated
the amplitude of the GW background at nHz frequencies to be on the order of
$1.4\cdot10^{-16} - 1.1\cdot10^{-15}$. This value depends solely on the time
delay between the merger of galaxies and their MBHs.
