  In this paper, we study asymptotic behavior of positive ground state
solutions for the nonlinear Choquard equation: \begin{equation}\label{0.1}
-\Delta u+\varepsilon u=\big(I_{\alpha}\ast F(u)\big)F'(u),\quad u\in
H^1(\mathbb R^N), \end{equation} where $F(u)=|u|^{\frac{N+\alpha}{N-2}}+G(u)$,
$N\geq3$ is an integer, $I_{\alpha}$ is the Riesz potential of order
$\alpha\in(0,N)$, and $\varepsilon>0$ is a parameter. Under some mild
subcritical growth assumptions on $G(u)$, we show that as $\varepsilon \to
\infty$, the ground state solutions of \eqref{0.1}, after a suitable rescaling,
converge to a particular solution of the critical Choquard equation $-\Delta
u=\frac{N+\alpha}{N-2}(I_{\alpha}*|u|^{\frac{N+\alpha}{N-2}})|u|^{\frac{N+\alpha}{N-2}-2}u$.
We establish a novel sharp asymptotic characterisation of such a rescaling,
which depends in a non-trivial way on the asymptotic behavior of $G(u)$ at
infinity and the space dimension $N=3$, $N=4$ or $N\geq5$.
