  Motivated by the ${\rm \Psi}$-Riemann-Liouville $({\rm \Psi-RL})$ fractional
derivative and by the ${\rm \Psi}$-Hilfer $({\rm \Psi-H})$ fractional
derivative, we introduced a new fractional operator the so-called
$\rm\Psi-$fractional integral. We present some important results by means of
theorems and in particular, that the $\rm\Psi-$fractional integration operator
is limited. In this sense, we discuss some examples, in particular, involving
the Mittag-Leffler $({\rm M-L})$ function, of paramount importance in the
solution of population growth problem, as approached. On the other hand, we
realize a brief discussion on the uniqueness of nonlinear $\Psi$-fractional
Volterra integral equation (${\rm VIE}$) using $\beta-$distance functions.
