We study Hankel operators on the standard Bergman spaces $A^{2}_{\alpha}, \alpha > -1$. A description of the boundedness and compactness of the (big) Hankel operator $H_f$ with general symbols $f \in L^2 (\mathbb{D}, d A_\alpha)$ is obtained. Also, we provide a new proof of a result of Arazy-Fisher-Peetre on the membership in Schatten $p$-classes of Hankel operators with conjugate analytic symbols.