open access

https://hdl.handle.net/2115/97511

Interaction between body size and commencement of smoltification in masu salmon Oncorhynchus masou

英語

photoperiod

2025-03-04

John Wiley & Sons

Journal of fish biology

This study analysed the relationship between body size and the commencement of smoltification in masu salmon Oncorhynchus masou. Juveniles of a strain of O. masou were reared under a simulated natural photoperiod (SNP) and an advanced photoperiod (AP), in which LD15:9 was interrupted by LD9:15 from June to October to induce spring smoltification. Regardless of the photoperiod, the underyearlings were just shorter than 12 cm in fork length (L-F) in October. When the photoperiod in the AP group was switched from short to long days in late October, juvenile O. masou exceeded 12 cm and exhibited increased gill Na+/K+-ATPase (NKA) activity in December. These changes were accompanied by an increase in circulating levels of insulin-like growth factor (IGF)-1 and IGF-binding protein-2b. In contrast, fish under SNP remained below 12 cm and had low gill NKA activity and hormone/protein levels from October to January. Underyearlings of the same strain reared in a larger tank under a natural photoperiod grew well and exhibited increased gill NKA activity in July when they exceeded 12 cm. These results suggest that an L-F of 12 cm is the threshold size above which juvenile O. masou increase gill NKA activity throughout the year. This implies that they may cease their growth during autumn and winter to avoid exceeding the threshold size required to commence smoltification during spring. Although the threshold size may be related to rearing density or tank size, the findings of the present study suggest that increases in gill NKA activity during summer and the following spring are tightly linked to body size in O. masou.

学術雑誌論文

Accepted Manuscript

This is the peer reviewed version of the following article: Ugachi, Y., Kitade, H., Takahashi, E., Izutsu, A., & Shimizu, M. (2025). Interaction between body size and commencement of smoltification in masu salmon Oncorhynchus masou. Journal of Fish Biology, 1–10, which has been published in final form at https://doi.org/10.1111/jfb.70010. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited.

0022-1112

1095-8649

AA00698121