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Vol. 52, 2013
Spatial variation in reproductive measures of female bluegill
Lepomis macrochirus Rafinesque in a small
lake with diverse thermal conditions
Yoshimasa
Yamamoto* and Fuh-Kwo Shiah
1Research
Center for Environmental Changes, Academia Sinica, 128 Academia Rd.,
Sec. 2, Taipei 11529, Taiwan
Abstract
Background: Our previous studies
have revealed that bluegill Lepomis
macrochirus Rafinesque
in Lake Biwa exhibit spatial variations in growth, maturation, and
reproduction. The topographical characteristics of Lake Biwa produce a
wide range of thermal conditions, which seem to be responsible for
those findings. Despite its small size, Lake Yogo is characterized by
diverse thermal conditions owing to the presence of a small, shallow
pool in the northern part of the lake and the inflow of water from Lake
Biwa into the southern part of the lake. Whether bluegill in such a
small lake also exhibit spatially varying physiological activity
remains uncertain.
Results: The maturation status of female bluegill
in Lake Yogo was investigated from late April to early June 2011 and in
late May 2012. The gonadosomatic index (GSI) of the fish in the pool
significantly exceeded those in the main lake in late April and mid-May
2011 before the onset of spawning. The spawning of bluegill had
probably already begun by late May 2012, and the fish in the pool and
along the northwestern edge of the lake had smaller GSIs than did the
fish in the southern part of the lake. The relationship between oocyte
diameter and GSI could be described by a saturation function. The plot
of GSI/oocyte diameter vs. GSI did not vary significantly among the
sites.
Conclusions: The maturation status
of bluegill varied among sites in Lake Yogo, likely to be due to the
diverse thermal conditions of the lake. Higher temperatures in the pool
during the prespawning season favored the rapid maturation of ovaries
of the fish therein. The inflowing colder water from Lake Biwa seemed
to be responsible for delayed ovary maturation and, thereby, the delay
in the spawning season of bluegill in the southern part of the lake.
Key words: Bluegill; Lake Yogo; Gonadosomatic
index; Oocyte; Thermal condition.
*Correspondence: E-mail: yyama@rcec.sinica.edu.tw
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