He studied both major and minor planets, and discovered multiple asteroids.
[2] Koishikawa was a staff member of the Sendai Astronomical Observatory frin 1972.
His research was based out of the Sendai's Ayashi (391) station.
The main-belt asteroid 6097 Koishikawa, discovered by Kin Endate and Kazuro Watanabe at Kitami in 1991, was named in his honor.
[2] He died on 26 August 2020 from lung cancer.