open access

https://doi.org/10.14943/doctoral.k12856

https://hdl.handle.net/2115/87560

異なる餌条件と水温におけるマダラ仔稚魚の遊泳行動に関する研究

英語

2017-09-25

Hokkaido University

ix, 57p

Pacific cod Gadus macrocephalus is an important fish species in fishery resource and marine ecosystem in the Northern Pacific Ocean. In Mutsu Bay Japan, cod larvae potentially experience complex thermal conditions and temporary food absence during pelagic life stages, due to varied hatching locations and uneven prey mass distribution. After settlement, juvenile (age-0) cod are transported to the area with drastic changes in temperature and may also suffer temporary food shortage resulted from separations from prey under thermal extremes. Little is known about the relationship between their behavioral responses and the environmental variables (i.e. varying temperatures and prey availability), despite its critical roles of in growth, survival and recruitment of this species. The objective of this study was to clarify the effects of temperature and recent feeding history on vertical distribution and swimming activity of larvae and age-0 juveniles of Pacific cod. Vertical distribution and swimming activity were tested in simulated (normal and reversed) temperature gradients with two ranges (4–8°C and 8–12°C) and at cold, moderate and warm temperatures (4, 8 and 12°C). Larvae were tested at two exogenous feeding stages: young (14–17 days after hatching [dah]) and old (28 and 29 dah). All the fish were either well fed (WF) or food-deprived (FD) for 24h. Most young maintained upper distribution and old were distributed lower in the temperature gradients, regardless of temperature or recent feeding history. Swimming activity of young larvae tended to increase with temperature, regardless of recent feeding history. Swimming activity of old larvae was independent of temperature and significantly reduced when larvae were deprived of food. Juvenile cod showed varied responses to the temperature gradients based on recent feeding history. WF juveniles accessed to both the cold and warm temperatures, while FD juveniles preferred the moderate temperature. Swimming activity of WF juveniles was significantly higher at 12°C than those similar ones at 4 and 8°C. Swimming activity of FD juveniles was significantly lower at 4°C than those similar ones at 8 and 12°C. Vertical distributions may be alternatively dominated by negative and positive geotaxis in cod larvae. In warm conditions, the young larvae are suggested to suffer higher starvation risk than the old larvae, because the latter can save energy by reducing swimming activity. Age-0 juveniles are suggested to have more flexible responses to varying temperatures and prey availability, compared to cod larvae. WF juveniles may utilize increased swimming activity in warm temperatures to improve feeding opportunity and growth rate. They appeared to be able to adapt to the cold temperature. FD juveniles might balance energy expenditure and substantial swimming activity in the moderate temperature In conclusion, behavioral responses of cod larvae to the environmental variables were less flexible that those of age-0 juvenile cod possessing ability to regulate thermal experience and swimming activity based on recent feeding. In warm conditions, the young larvae are expected to be more susceptible to temporary food shortage compared with older larvae, and age-0 juveniles are expected to have stronger environmental resistance compared to the cod larvae.

2017-09-25

甲第12856号

博士(水産科学)

(主査) 教授 高津 哲也, 教授 綿貫 豊, 准教授 山村 織生

水産科学院（海洋生物資源科学専攻）

博士論文

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