|
Vol. 49 No. 5, 2010
Latitudinal Gradient in the Body Weight of Bluegill Lepomis macrochirus in Lake Biwa, Japan
Yoshimasa Yamamoto1,2,*, Hajime Tsukada1,3, and Daisuke Nakai1,4
1Division
of Applied Biosciences, Graduate School of Agriculture, Kyoto Univ.,
Kitashirakawaoiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan
2Research Center for Environmental Changes, Academia Sinica, 128 Academia Rd., Sec. 2, Taipei 11529, Taiwan
3Environmental Optimization Laboratory, 2-12-12 Innai, Chuo-ku, Chiba 260-0018, Japan
4Yu Group, OhmiRailway, 4-7 Awazu-cho, Shiga 520-0832, Japan
Yoshimasa Yamamoto, Hajime Tsukada, and Daisuke Nakai (2010) Variations in the body weight of bluegill Lepomis macrochirus
among 10 coastal regions of Lake Biwa and 11 lagoons of the lake were
studied in Oct. 2005 and Oct. 2007, respectively. The body
weights of fish with a normalized total length were estimated from
length-weight relationships determined at each site. Body weights
of bluegill from the lake and lagoons increased linearly with
latitude. Additionally, there was a negative correlation between
the calculated body weight and the number of sampled bluegill per unit
time from the lagoons, implying that the population density of bluegill
may strongly influence its growth in lagoons. Increasing numbers
of submerged plants have covered the lake area in recent years,
especially in the shallow southern basin. Moreover, as a predator
of bluegill, the largemouth bass Micropterus salmoides appears to
flourish at higher densities in the northern basin of the lake than in
the southern basin. These biotic factors seem to be somewhat
responsible for the significant difference between the northern and
southern basins in terms of the body weight of bluegill. However,
water temperature and population density of the bluegill appear to be
more directly responsible for the latitudinal variation in bluegill
growth in Lake Biwa.
Key words: Bluegill, Body weight, Length-weight relationship, Latitude, Lake Biwa.
*Correspondence: Tel: 886-2-2653-9885. Fax: 886-2-2783-3584. E-mail:yyama@rcec.sinica.edu.tw
|
