Vol. 51 No. 8, 2012

Spatial Variation in the Spawning Season of Bluegill Lepomis macrochirus in Lake Biwa, Japan

Yoshimasa Yamamoto* and Fuh-Kwo Shiah

Research Center for Environmental Changes, Academia Sinica, Nankang, Taipei 115, Taiwan

Yoshimasa Yamamoto and Fuh-Kwo Shiah (2012) Reproductive condition of bluegill Lepomis macrochirus was examined at 3 sites in Lake Biwa, Japan, in an attempt to investigate spatial variation in their spawning season.  Analytical results showed that the gonadosomatic index (GSI) of fish at all sites increased from mid-May to early June.  Although the GSI of fish at the southernmost and mid-latitude sites decreased from early to late June, the GSI decline was much more severe in fish at the southernmost site.  In contrast, fish at the northernmost site exhibited no significant difference in GSI between early and late June.  The proportion of females containing mature eggs decreased with latitude in early June but increased with latitude in late June, implying that bluegill at the southernmost site actively spawned in June and were in the final stage of spawning in late June, whereas fish at the northernmost site were still actively spawning in late June.  These results suggest that the spawning season of bluegill in Lake Biwa varies from site to site; fish at lower latitudes begin to spawn earlier, and those at higher latitudes may have a longer spawning season.

Key words: Bluegill, Lake Biwa, Gonadosomatic index, Oocyte, Spawning season.

*Correspondence: Tel: 886-2-26539885.  Fax: 886-2-27833584.  E-mail:yyama@rcec.sinica.edu.tw