Photoperiodic control of smoltification and aspects of broodstock management in Atlantic salmon, Salmo salar

• Main Author: Thrush, Mark Adrian
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of Stirling 1994
• Subjects: Smolting; Atlantic salmon Breeding; Atlantic salmon Spawning; Brood stock assessment; Atlantic salmon; Salmo salar
• Online Access: http://hdl.handle.net/1893/29305; http://dspace.stir.ac.uk/bitstream/1893/29305/1/Thrush.pdf

At present, the restricted temporal availability of Atlantic salmon smolts leads to a seasonal supply of marketable salmon and as a consequence an unstable price. The development of smoltification appears to be controlled by the .seasonal changes in daylength. The primary aim of this thesis, in collaboration with commercial smolt producers and on- growers, was to achieve a “year-round” supply of Atlantic salmon using photoperiod techniques. Potential SI (l-l-) and S2 (2+) Atlantic salmon smolts were reared in freshwater under compressed and extended seasonally-changing photoperiods and under ‘square wave’ (direct change from short to long) light regimes. Pre-smolts underwent body silvering and fin darkening, a reduction in condition factor and developed strong hypo-osmoregulatory ability in respon.se to increasing daylengths. In this study, the completion of smoltification was advanced by a maximum of 3- and 7- months among potential S 1 and potential S2 smolts respectively, and was delayed by 1-month among potential S2 smolts. The results were consistent with the hypothesis that changes in daylength entrain an endogenous circannual timing mechanism which controls the development of smoltification. Results were also consistent with the hypothesis that a ‘decision to smolt’ is made under the influence of a decreasing daylength in the year preceding seaward migration. Furthermore, It was apparent that this decision period may extend into the winter and that recruitment into the smolting fraction is probably terminated by the increasing daylength after the winter solstice. Parr reared under a compressed photoperiod with low intensity night-time illumination failed to complete smoltification at the same time as tho.se without night-time illumination. Serum melatonin was elevated throughout the period of the low intensity pha.se among fish maintained on the dual light intensity regime, although peak levels were attenuated compared to fish reared under light-dark cycles in other published studies. Temporally advanced ...