  It has been shown that the nonthermal spectrum of Hawking radiation will lead
to information-carrying correlations between emitted particles in the
radiation. The mutual information carried by such correlations can not be
locally observed and hence is dark. With dark information, the black hole
information is conserved. In this paper, we look for the spherically symmetric
black hole solution in a $\lambda\varphi$ fluid model and investigate the
radiation spectrum and dark information of the black hole. The spacetime
structure of this black hole is similar to that of the Schwarzschild one, while
its horizon radius is decreased by the $\lambda\varphi$ fluid. By using the
statistical mechanical method, the nonthermal radiation spectrum is calculated.
This radiation spectrum is very different from the Schwarzschild case at its
last stage because of the effect of the $\lambda\varphi$ fluid. The
$\lambda\varphi$ fluid reduces the lifetime of the black hole, but increases
the dark information of the Hawking radiation.
