Energy dependence of fission observables is a key issue for wide nuclear applications. We studied real-time fission dynamics from low-energy to high excitations in the compound nucleus ${}^{240}\mathrm{Pu}$ with the time-dependent Hartree-Fock $+$ BCS approach. It is shown that the evolution time of the later phase of fission towards scission is considerably lengthened at finite temperature. As the role of dynamical pairing is vanishing at high excitations, the random transition between single-particle levels around the Fermi surface to mimic thermal fluctuations is indispensable to drive fission. The obtained fission yields and total kinetic energies with fluctuations can be divided into two asymmetric scission channels, namely, S1 and S2, which explain well experimental results and give microscopic support to the Brosa model. With increasing fluctuations, the S2 channel takes over the S1 channel and the spreading fission observables are obtained.

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• Fission
• Nuclear density functional theory
• Nuclear forces
• A ≥ 220