Longest Running Manga by Volume Count (1-50)
Manga
No. 26 is Hakuryuu, which started in 1996. I have put Hakuryuu Legend instead because I could not find an earlier version.
No. 30 is Kabachitare! by Takashi Tajima & Takahiro Kochi, which started in 1999 and is ongoing with 93 volumes & 974 chapters in Weekly Morning Kodansha.
No. 34 is Inochi no Utsuwa by Kimiko Uehara, which started in 1991 and is ongoing with 89 volumes & 348 chapters in For Mrs. Akita Shoten.
No. 46 is Somubu Somuka Yamaguchi Roppeita by Norio Hayashi & Yamaguchi Roppeita, which started in 1986 with 81 volumes & 731 chapters in Big Comic Shogakukan.
Number of volumes and chapters in notes.
No. 30 is Kabachitare! by Takashi Tajima & Takahiro Kochi, which started in 1999 and is ongoing with 93 volumes & 974 chapters in Weekly Morning Kodansha.
No. 34 is Inochi no Utsuwa by Kimiko Uehara, which started in 1991 and is ongoing with 89 volumes & 348 chapters in For Mrs. Akita Shoten.
No. 46 is Somubu Somuka Yamaguchi Roppeita by Norio Hayashi & Yamaguchi Roppeita, which started in 1986 with 81 volumes & 731 chapters in Big Comic Shogakukan.
Number of volumes and chapters in notes.

Manga, 200 vol, 1976
Me:-
Author:-
201 volumes & 1960 chapters
Ginga Nagareboshi Gin
Silver Fang: The Shooting Star Gin

Manga, 18 vol, 1983
Me:-
Author:-
147 volumes & 1097 chapters
Hajime no Ippo
Hajime no Ippo: Fighting Spirit!

Manga, ? vol, 1989
Me:-
Author:10
137 volumes & 1420 chapters
JoJo no Kimyou na Bouken Part 1: Phantom Blood
JoJo's Bizarre Adventure Part 1: Phantom Blood

Manga, 5 vol, 1986
Me:-
Author:8
132 volumes & 962 chapters
Urayasu Tekkin Kazoku
Super Radical Gag Family

Manga, 31 vol, 1993
Me:-
Author:-
98 volumes & 1451 chapters
Koutarou Makaritooru!
Koutarou Breakthrough!

Manga, 59 vol, 1982
Me:-
Author:-
94 volumes & 464 chapters
Kindaichi Shounen no Jikenbo: File Series
The Kindaichi Case Files

Manga, 27 vol, 1992
Me:-
Author:-
92 volumes & 727 chapters
Tobaku Mokushiroku Kaiji
Gambling Apocalypse Kaiji

Manga, 13 vol, 1996
Me:-
Author:-
85 volumes & 831 chapters