  In this work, we investigated the decays of the fully open-flavor tetraquark
state $X_0(2900)$ which was observed by the LHCb Collaboration very recently.
Here, the $X_0(2900)$ was assigned as a $S-$wave $\bar D^\ast K^\ast$ hadronic
molecule with $I=0$, and the effective lagrangian approach was applied to
estimate the partial decay widths. Moreover, we also predicted the decay
behaviors of the other unobserved $X_{J(J=1,2)}$, which were the spin partners
of the $X_0(2900)$ in the $S-$wave $\bar D^\ast K^\ast$ picture. It was pointed
out that the $X_1$ state with $I=0$ was a broad state with the width more than
one hundred MeV, while another $X_2$ state with $I=0$ was a narrow state with
the width approaching half of that for the $X_0(2900)$. In addition, our
results also showed that the $\bar D^\ast K$ mode was expected to be the
dominant decay mode for both $X_1$ and $X_2$. Searching for those unobserved
$X_{J(J=1,2)}$ in the future experiments might be helpful to understand the
nature of $X_0(2900)$.
