Fission-fragment mass distributions for 23 nuclei (U234-237, Np236-239, Pu238-241, Am240-243, Cm242-245, and Bk244-246) were measured using the multinucleon transfer approach in the reaction of O-18 + Np-237, and their excitation-energy dependence was obtained up to a maximum of 70 MeV. Among them, the low-energy fission of Np-236, Pu-238, and Cm-245 is reported for the first time. The experimental data for all the studied nuclei were compared to the Langevin calculations. The calculation which takes into account the effects of multichance fission well reproduced the peak-to-valley ratio and mass-asymmetric peak positions of the distributions. The angular momentum given to the fissioning nucleus is also discussed.