Photoperiod revisited: is there a critical day length for triggering a complete parr–smolt transformation in Atlantic salmon Salmo salar?

• Published in: Journal of Fish Biology
• Main Authors: Strand, Jo Espen Tau, Hazlerigg, David, Jørgensen, Even Hjalmar
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2018
• Subjects: VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920; VDP::Landbruks- og Fiskerifag: 900::Fiskerifag: 920; day length; photoperiod; Salmo salar; salmon smolt; Atlantic salmon
• Online Access: https://hdl.handle.net/10037/14053; https://doi.org/10.1111/jfb.13760

This is the peer reviewed version of the following article: Strand, J.E.T., Hazlerigg, D., Jørgensen, E.H. (2018). Photoperiod revisited: is there a critical day length for triggering a complete parr–smolt transformation in Atlantic salmon Salmo salar? Journal of Fish Biology, 93, 440-480. https://doi.org/10.1111/jfb.13760, which has been published in final form at https://doi.org/10.1111/jfb.13760 . This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. The present study investigated whether there is a critical length of photoperiod needed to stimulate a completed parr–smolt transformation (PST) in Atlantic salmon Salmo salar . In two experiments, S. salar parr of the Norwegian aquaculture strain held on continuous light were exposed to a short photoperiod (6 L:18D) followed by exposure to 8 L:16D, 12 L:12D, 16 L:8D, 20 L:4D and 24 L:0D in experiment 1 or to 6 L:18D followed by maintenance on 6 L:18D or exposure to 12 L:12D and 24 L:0D photoperiods in experiment 2. All groups, irrespective of photoperiod treatment, developed improved hypo‐osmoregulatory ability. However, the development was greatest in the groups exposed to 20 L:4D and 24 L:0D in experiment 1 and 24 L:0D in experiment 2. In experiment 2, gill Na+– K+‐ATPase activity increased in the group exposed to 24 L:0D, but not in the groups exposed to 12 L:12D and 6 L:18D. The groups exposed to 20 L:4D and 24 L:0D in experiment 1 and 24 L:0D in experiment 2 also grew better than fish exposed to shorter photoperiods. In experiment 2 only the group exposed to 24 L:0D showed a decrease in condition factor and increases in plasma growth hormone and brain type 2 deiodinase mRNA abundance. Hence, only the groups exposed to photoperiods above 16 L:8D developed classical smolt indices in the present experiment, leading us to conclude that the photoperiod increase needs to exceed 16 h daylight for stimulating a complete PST in the S. salar used in the present study.