Optimum survival temperature for walleye pollock larvae
Ryo Nakagawa1, Takashi Yokota1, Hiroshige Tanaka2, Yukimasa Chimura2, Yuho Yamashita2
and Tetsuichiro Funamoto2
1
Hokkaido National Fisheries Research Institute, Fisheries Research Agency, Akkeshi, Hokkaido, Japan
Hokkaido National Fisheries Research Institute, Fisheries Research Agency, Kushiro, Hokkaido, Japan
E-mail: tetsuf@fra.affrc.go.jp
2
For walleye pollock (Gadus chalcogrammus) around Japan, a strong relationship is observed
between water temperature during early life stages and recruitment. However, the mechanism
underlying this relationship is still unclear. In this study, to examine the effects of water
temperature on growth and survival of pollock larvae under different feeding conditions, pollock
larvae hatched in the laboratory were reared at two feeding levels and three temperatures.
Feeding level was varied by providing low temperature-resistant rotifers (Brachionus plicatilis
sp. complex) every day or every three days, and at each feeding level, larvae were reared at 3º, 6º,
and 10ºC. Under both feeding conditions, larval body lengths (BL) at 21 days after hatching were
in the order: 10ºC>6ºC>3ºC. On the other hand, larval survival rates were 6ºC>3ºC>10ºC. In
addition, the mortality coefficient per 1mm increased with BL, which was calculated from BL
and survival rate, and increased in the order of 6º, 3º, and 10ºC. These results indicate that, under
feeding and thermal conditions examined in this study, larval survival for the same growth rate is
best at 6ºC irrespective of feeding levels, although larval growth is faster at higher temperatures.
It is suggested that this optimum larval survival temperature around 6ºC is one of the main
causes of the relationship between water temperature and pollock recruitment.