We study the following nonlinear fractional Choquard equation:
$${\epsilon}^{2s}{\left(\Delta \right)}^{s}w+V\left(x\right)w={\epsilon}^{\theta}W\left(x\right)\left[{I}_{\theta}\ast \left(Ww{}^{p}\right)\right]w{}^{p2}w,\phantom{\rule{1em}{0ex}}x\in {\mathbb{R}}^{N},$$  ($\star $) 
where
$\epsilon >0$,
$s\in \left(0,1\right)$,
$N>2s$,
${I}_{\theta}$ is the Riesz
potential with order
$\theta \in \left(0,N\right)$,
$p\in \left[2,\frac{N+\theta}{N2s}\right)$,
$\underset{{\mathbb{R}}^{N}}{min}V>0$ and
$\underset{{\mathbb{R}}^{N}}{inf}W>0$. By
specifying the ranges and interdependence of linear and nonlinear potentials, we achieve
the existence, convergence, concentration, and decay estimate of positive groundstates
for $\star $.
The multiplicity of semiclassical solutions is established via pseudoindex theory. The
existence of signchanging solutions is constructed by minimizing the energy on
Nehari nodal set.
