Pulsed blue light at $489\mathrm{nm}$ has been generated by second-harmonic-generation of a nanosecond pulsed master- oscillator power amplifier system based on a short ${\mathrm{Yb}}^{3+}$ doped single-mode fiber amplifier at $978\mathrm{nm}$ and an external-cavity diode laser as seed source. The ${\mathrm{Yb}}^{3+}$ -doped fiber was core-pumped by a W type ${\mathrm{Nd}}^{3+}$ doped double- clad fiber laser operating on the transition near $930\mathrm{nm}$ ( ${}^4{\mathrm{F}}_{3/2}\to {}^4{\mathrm{I}}_{9/2}$ ). $520\mathrm{mW}$ of average power was generated at $489\mathrm{nm}$ using a periodically poled $\mathrm{MgO}\text{:}{\mathrm{LiNbO}}_3$ , corresponding to a conversion efficiency of 34%.