Differences in self-feeding activity between thermally selected and normal strains of rainbow trout Oncorhynchus mykiss at high temperatures


  • Toshinao INENO,

    Corresponding author
    1. Miyazaki Prefectural Fisheries Experimental Station Kobayashi Branch, Kobayashi, Miyazaki 886-0005,
    Search for more papers by this author
    • a

      Present address: Fisheries Promotion and Infrastructure Division, Agriculture and Fisheries Department, Miyazaki Prefecture, Miyazaki 880-8501, Japan.

  • Makoto ENDO,

    1. Laboratory of Fish Health Management, Department of Marine Biosciences, Tokyo University of Marine Science and Technology, Minato, Tokyo 108-8477, and
    Search for more papers by this author
  • Shugo WATABE

    1. Laboratory of Aquatic Molecular Biology and Biotechnology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo, Tokyo 113-8657, Japan
    Search for more papers by this author

*Tel: 81-985-26-7147.
Fax: 81-985-26-7310. Email: ineno-toshinao@pref.miyazaki.lg.jp


ABSTRACT:  Feeding activity was examined at high temperatures by using a demand feeder for thermally selected and normal rainbow trout Oncorhynchus mykiss strains. When the water temperature was raised in experiment 1 from 17.5 to 25.7°C at 0.3°C/day in 21 days, the average daily food consumption rate in the thermally selected strain rose to 7.1%, which was significantly higher than that of the normal strain (4.1%, P < 0.05). The corresponding rate was also significantly higher in the thermally selected (0.8%) than in the normal strain (0.2%, P < 0.05) of fish in experiment 2 where water temperature was raised to 24.1°C in 0.5°C/day increments. When water temperature was raised rapidly in experiment 3 from 16.7 to 21.7°C in one day and gradually to 24.4°C in 28 days at 0.1°C/day, the average daily food consumption rates were 1.0 and 0.1% for the thermally selected and normal strains, respectively, with significant difference (P < 0.01). These results suggest that the thermally selected strain has acquired thermal tolerance as a result of artificial selection.